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If you’re curious to know what my book is about and why it’s called “Waves in an Impossible Sea”, then watching this video is currently the quickest and most direct way to find out from me personally. It’s a public talk that I gave to a general audience at Harvard, part of the Harvard Bookstore science book series.

My intent in writing the book was to illuminate central aspects of the cosmos — and of how we humans fit into it — that are often glossed over by scientists and science writers, at least in the books and videos I’ve come across. So if you watch the lecture, I think there’s a good chance that you’ll learn something about the world that you didn’t know, perhaps about the empty space that forms the fabric of the universe, or perhaps about what “quantum” in “quantum physics” really means and why it matters so much to you and me.

The video contains 35 minutes of me presenting, plus some Q&A at the end. Feel free to ask questions of your own in the comments below, or on my book-questions page; I’ll do my best to answer them.

On my recent trip to CERN, the lab that hosts the Large Hadron Collider, I had the opportunity to stop by the CERN control centre [CCC]. There the various particle accelerator operations are managed by accelerator experts, who make use of a host of consoles showing all sorts of data. I’d not been to the CCC in person — theoretical physicists congregate a few kilometers away on another part of CERN’s campus — although back in the LHC’s very early days, when things ran less smoothly, I used to watch some of the CCC’s monitoring screens to see how the accelerator was performing.

The atmosphere in the control room was relatively quiet, as the proton-proton collisions for the year 2024 had just come to an end the previous day. Unlike 2023, this has been a very good year. There’s a screen devoted to counting the number of collisions during the year, and things went so well in 2024 it had to be extended, for the first time, by a “1” printed on paper.

The indication “123/fb” means “123-collisions-per-femtobarn”, while one-collision-per-femtobarn corresponds to about 1014 = 100,000,000,000,000 proton-proton collisions. In other words, the year saw more than 12 million billion proton-proton collisions at each of the two large-scale experiments, ATLAS and CMS. That’s about double the best previous year, 2018.

Yes, that’s a line of bottles that you can see on the back wall in the first photo. Major events in the accelerator are often celebrated with champagne, and one of the bottles from each event is saved for posterity. Here’s one from a few weeks ago that marked the achievement of 100-collisions-per-femtobarn.

With another one and a half seasons to go in Run 3 of the LHC, running at 13.6 TeV of energy per collision (higher than the 13 TeV per collision in Run 2 from 2015 to 2018, and the 7 and 8 TeV per collision in Run 1 from 2010 to 2012), the LHC accelerator folks continue to push the envelope. Much more lies ahead in 2029 with Run 4, when the collision rate will increase by another big step.

Recently a reader, having read my post about why the speed of light seems so fast, sent me two questions that highlight important cosmic issues.

1. Is there in fact anything within physics as it’s presently understood that indeed prevents […] there existing something other than atoms as some basic “unit”?
   
2. I’ve long wondered why it is that despite the seeming brilliance of humans at building such complex understanding, we are still pushing at such limits as the time it would take to fly a space ship to another galaxy. Is it really true that nothing could ever exceed ‘c’ and thus we are indeed doomed to take lifetimes to travel beyond our solar system? Or is it because we have not yet discovered something much more fundamental about the universe, such as an ‘alternative to’ the atom?

These deep questions are examples of an even broader pair of questions about reality.

• Which aspects of the cosmos are contingent?—in that one could easily imagine a similar universe in which these details are thoroughly altered.
• Which aspects of the cosmos appear rock solid?—in that they are so deeply integrated into the universe that it is difficult to imagine changing them without ruining everything.

Could something other than atoms serve as a basic material unit?

The answer to this question is “absolutely yes.”

If we look at the composite objects that make up ordinary matter, we are looking at specific particles and specific forces. There are four levels of composite objects:

• protons and neutrons made from quarks and gluons via the strong nuclear force
• atomic nuclei made from protons and neutrons via the residual strong nuclear force
• atoms made from nuclei and electrons via the electromagnetic force
• molecules made from atoms via the (often residual) electromagnetic force

But the details are complex and have to do with the precise natures of the particles and the forces. A universe with different particles and/or different forces might make entirely unfamiliar composite objects—or none at all.

Here’s where the power of theoretical physics shows itself. We can in some cases calculate what would happen in an imaginary universe with its own types of particles and forces, and gain some insights into the composite objects that might result. More challenging is to figure out whether some macroscopic material, analogous to the ordinary large-scale solids and fluids we’re familiar with, could exist in that universe. But it’s easy to show that many types of composite objects could potentially exist in other, imaginary universes, and though different from our familiar atoms, they could nevertheless serve as building blocks for complex materials.

How about in our own, real universe? There’s still a lot we don’t know about it. Experiments leave open the possibility that there are types of particles that we haven’t yet discovered, perhaps entire classes of them. There are two reasons we might not have found them.

• Too Much Mass: If a particle’s mass is very large (roughly a thousand times the mass of a typical atom, or more), then we can’t make it directly in our particle accelerators; and if such particles are also rare in the universe, with very few of them surviving from the Big Bang, then we would neither find them on purpose nor by accident. They might form unknown forms of composite objects, through either known or unknown forces.
• Too Hidden: If a type of particle is insensitive to the known types of forces (excepting gravity), then our experiments would neither detect their presence nor be able to produce them directly. Such particles are referred to as “hidden” or “dark”. They might even make up dark matter, giving us a hint of their existence through their gravity, but no other direct information that would help us learn their details. If they interact with each other via their own set of forces, those forces might allow them to make unknown and hidden composite objects.

For some types of particles, both of these reasons could simultaneously be true.

Composite objects formed by these unknown particles, through known or unknown forces, could potentially be as complex and variegated as atoms. As an example, researchers have taken seriously the possibility that dark matter is made from some sort of exotic atom, formed from dark elementary particles and forces, and asked about the particle physics and astrophysics consequences. (Here’s one paper on the subject; here’s another more recent one.)

And so, both theoretical considerations and existing experiments allow for the possibility of an unknown material made from unknown basic building blocks or units. This is true both in the abstract, where we imagine other possible universes, and in the concrete, in that it may even be true in our own universe. It may be that dark matter, or some other substance as yet unknown, has this property.

Can the speed of light be exceeded?

Before answering this, one must state carefully what one means by this question; I have pointed out pitfalls here. The proper form of the question is:

• When two objects pass each other, could an observer traveling with one object find that the speed of the second object is higher than the cosmic speed limit?

(If you ask the question in the wrong way — for instance, if you ask, can I observe two objects whose relative motion is faster than the speed of light from my point of view? — then the answer is “yes, and it happens all the time; just look at two oppositely-directed flashlight beams, or, as viewed from the laboratory, the two proton beams in the Large Hadron Collider.” Clearly that’s not what the reader is asking.)

In any universe in which Einstein’s view of gravity (known as general relativity) is true, for which local processes are described by special relativity, taught in first-year physics classes, the answer would be firmly “no.” In such a universe, there is a unique, unbreakable cosmic speed limit that applies to all objects equally. The very nature of space and time prevent anything from breaking it.

For example, if you tried to overtake a light beam, you’d find that the faster you go, the faster the light would seem to go, too, making it impossible for you to catch up to it. (In my book, I called this the “nightmare property” of the universe, since it sounds uncannily like a certain type of bad dream.) No matter what you do to improve your chances, your experience of time and space will adjust in such a way that your efforts will fail. It’s not a matter of better technology. Even infinitely powerful technology cannot beat the universe’s basic structure.

It is widely believed that, in our universe, Einstein’s general relativity is correct to a very good approximation. It can’t be exactly correct, because it doesn’t meld well with quantum physics, which we know is another feature of our universe. When quantum physics meets space and time, it might not even be meaningful to define “speed”, at least not in a straightforward way. So there might be circumstances in which the cosmic speed limit does not apply in the ways we are used to.

However, it seems to me profoundly unlikely that any violation of the cosmic speed limit, induced perhaps by quantum physics, will permit humans to travel faster than light. We ourselves are creatures of ordinary space and time, and in any situation in which space and time behave in an extraordinary way, or in which we try to move across it an extraordinary way, would probably kill us. (I’ve just finished reminding you how fragile we are and why this means that we must travel slowly relative to our surroundings. As another unrelated but amusing example of this point, see section 3.4 of this paper, a light-hearted yet scientifically rigorous look at just how difficult it would be to make wormholes that humans or spacecraft could safely cross through.)

Even if you just wanted to send a message faster than light, you would presumably still want to be sending it across normally-defined space and time. The structure of the cosmos would likely ensure that you would fail.

This is not to say that we should be closed-minded about this question. Sometimes our understanding of the universe takes a strange twist, and there’s a lot about space and time that we don’t yet understand. But being open-minded is not the same as being empty-headed. Any chance of violating this basic cosmic constraint on space-time, at least in any way that would affect our ability to cross the cosmos, currently seems like a very, very long shot.

One more point: could there be imaginary universes with no cosmic speed limit at all? Maybe. But in such a universe, extremely distant events in the universe could potentially have an instantaneous impact on our lives. Cause and effect might be harder to understand, and it’s not clear (to me, anyway) that such a universe would function well.

Final cosmic thoughts about speed and time

The bottom line:

1. No principle or experiment forbids the existence of unknown materials made from unknown basic objects, much as familiar matter is made from atoms.
2. The existence of a cosmic speed limit seems to be a basic structural element of the universe; this statement is suggested by theoretical principles and has a solid experimental basis (see for instance this recent paper).

So it turns out, though this would hardly have been obvious a century ago, that it’s much easier to imagine replacing atoms with something else than to evade the cosmic speed limit.

As a last thought, let me add something regarding this part of the reader’s second question:

• Is it really true that nothing could ever exceed ‘c’ and thus we are indeed doomed to take lifetimes to travel beyond our solar system?

“Yes” for the first half of the question; but “no” (in a sense) for the second.

Even though nothing can exceed the cosmic limit under any familiar circumstances, it is still true that time can play tricks, as it behaves unexpectedly in our universe. It is possible in principle (though probably impossible practically, due to the difficulty of building suitably safe rockets) for you to travel to many stars, even all across our entire galaxy, in your lifetime. Unfortunately, for those left behind on Earth, your trip will take far longer than their lifetimes.

This is sometimes called the “twin paradox” (and it underlies the emotional plot of the movie Interstellar) but there’s nothing paradoxical about it. It’s just unfamiliar. It rests on a basic fact: the amount of time that you measure between one event and another depends on the nature of the journey that you took to get from the initial event to the final one.

Said another way: time is something experienced by each object separately, as measured by a clock carried along with that object, and it depends on how the object moves around within the universe. There is no universal clock that exists across the universe, and outside individual observers and objects, that can measure some universal notion of time.

Specifically, the amount of time that elapses for someone traveling far from Earth to distant stars and then returning home can be far less than the amount of time that elapses meanwhile on Earth. This is not an illusion or a trick; it’s just a fact about time that’s not at all obvious from daily life. The consequence is that you yourself could visit many stars, but your friends or family (and multiple generations after them) would be long dead when your rocket landed back on Earthly soil.

(Note: In a perfectly smooth and uniform universe, there would be some reasonable notion of “universal time”; and since our universe is approximately uniform on very large distance scales, there is an approximate notion of universal time, which is quite similar to Earth time, that is useful on very large distance scales. That’s why we can talk about “the time since the Big Bang”, using this approximate universal time, and say that the universe is 13.8 billion years old; it’s approximately true for observers and objects that have not moved rapidly relative to the average objects in the universe, such as typical galaxies and our own planet. But this universal time does not apply to, say, individual observers taking extremely rapid, complex round trips around the galaxy. Such observers may live far longer than 100 years of approximate universal time — though for each of them, life will feel just as long as it does for us, because the rate of their thinking, breathing and metabolism relative to the time they experience is the same as it is for any human. Again, see the movie Interstellar for illustrations of this effect.)

Geneva, Switzerland, is not known for its sunny weather, and seeing the comet here was almost impossible, though I caught some glimpses. I hope many of you have seen it clearly by now. It’s dim enough now that dark skies and binoculars are increasingly essential.

I came here (rather than the clear skies of, say, Morocco, where a comet would be an easier target) to give a talk at the CERN laboratory — the lab that hosts the Large Hadron Collider [LHC], where the particle known as the Higgs boson was discovered twelve years ago. This past week, members of the CMS experiment, one of the two general purpose experiments at the LHC, ran a small, intensive workshop with a lofty goal: to record vastly more information from the LHC’s collisions than anyone would have thought possible when the LHC first turned on fifteen years ago.

The flood of LHC data is hard to wrap one’s head around. At CMS, as at the ATLAS and LHCb experiments, two bunches of protons pass through each other every 40 billionths of a second. In each of these “bunch crossings”, dozens of proton-proton collisions happen simultaneously. As the debris from the collisions moves into and through the CMS experiment, many detailed measurements are made, generating roughly a megabyte of data even with significant data compression. If that were all recorded, it would translate to many terabytes produced per second, and hundreds of millions of terabytes per year. That’s well beyond what CMS can store, manage and process. ATLAS faces the same issues, and LHCb faces their own version.

So what’s to be done? There’s only one option: throw most of that data away in the smartest way possible, and ensure that the data retained is processed and stored efficiently.

Data Overload and the Trigger

The automated system that has the job of selecting which data to throw away and which to keep is called the “trigger”; I wrote an extended article about it back in 2011. The trigger has to make a split-second judgment, based on limited information. It is meant to narrow a huge amount of data down to something manageable. It’s has to be thoughtfully designed and carefully monitored. But it isn’t going to be perfect.

Originally, at ATLAS and CMS, the trigger was a “yes/no” data processor. If “yes”, the data collected by the experiment during a bunch crossing was stored; otherwise it was fully discarded.

A natural if naive idea would be to do something more nuanced than this yes/no decision making. Instead a strict “no” leading to total loss of all information about a bunch crossing, one could store a sketch of the information — perhaps a highly compressed version of the data from the detector, something that occupies a few kilobytes instead of a megabyte.

After all, the trigger, in order to make its decision, has to look at each bunch crossing in a quick and rough way, and figure out, as best it can, what particles may have been produced, where they went and how much energy they have. Why not store the crude information that it produces as it makes its decision? At worst, one would learn more about what the trigger is throwing away. At best, one might even be able to make a measurement or a discovery in data that was previously being lost.

It’s a good idea, but any such plan has costs in hardware, data storage and person-hours, and so it needs a strong justification. For example, if one just wants to check that the trigger is working properly, one could do what I just described using only a randomly-selected handful of bunch crossings per second. That sort of monitoring system would be cheap. (The experiments actually do something smarter than that [called “prescaled triggers”.])

Only if one were really bold would one suggest that the trigger’s crude information be stored for every single bunch crossing, in hopes that it could actually be used for scientific research. This would be tantamount to treating the trigger system as an automated physicist, a competent assistant whose preliminary analysis could later be put to use by human physicists.

Data “Scouting” a.k.a. Trigger-Level Analysis

More than ten years ago, some of the physicists at CMS became quite bold indeed, and proposed to do this for a certain fraction of the data produced by the trigger. They faced strong counter-arguments.

The problem, many claimed, is that the trigger is not a good enough physicist, and the information that it produces is too corrupted to be useful in scientific data analysis. From such a perspective, using this information in one’s scientific research would be akin to choosing a life-partner based on a dating profile. The trigger’s crude measurements would lead to all sorts of problems. They could hide a new phenomenon, or worse, create an artifact that would be mistaken for a new physical phenomenon. Any research done using this data, therefore, would never be taken seriously by the scientific community.

Nevertheless, the bold CMS physicists were eventually given the opportunity to give this a try, starting in 2011. This was the birth of “data scouting” — or, as the ATLAS experiment prefers to call it, “trigger-object-level analysis”, where “trigger-object” means “a particle or jet identified by the trigger system.”

The Two-Stage Trigger

In my description of the trigger, I’ve been oversimplifying. In each experiment, the trigger works in stages.

At CMS, the “Level-1 trigger” (L1T) is the swipe-left-or-right step of a 21st-century dating app; using a small fraction of the data from a bunch crossing, and taking an extremely fast glance at it using programmable hardware, it makes the decision as to whether to discard it or take a closer look.

The “High-Level Trigger” (HLT) is the read-the-dating-profile step. All the data from the bunch crossing is downloaded from the experiment, the particles in the debris of the proton-proton collision are identified to the extent possible, software examines the collection of particles from a variety of perspectives, and a rapid but more informed decision is made as to whether to discard or store the data from this bunch crossing.

The new strategy implemented by CMS in 2011 (as I described in more detail here) was to store more data using two pipelines; see Figure 1.

• More HLT “yes” votes were allowed, in which the experiment’s full and detailed information about a bunch crossing would be stored (“parked”) for months, before being processed just like data collected in the usual way.
  
• For certain HLT “no” votes, even though the full, detailed information about the bunch crossing was discarded, some of the high-level information from the HLT about the particles it identified was stored (“scouting”).

Effectively, the scouting pipeline uses the HLT trigger’s own data analysis to compress the full data from the bunch crossing down to a much smaller size, which makes storing it affordable.

Figure 1: Sketch of the data flow in 2011 at CMS, with the addition of parking and scouting data to the standard data collection (the top line). Data rate estimates are shown.

Being bold paid off. It turned out that the HLT output could indeed be used for scientific research. Based on this early success, the HLT scouting program was expanded for the 2015-2018 run of the LHC (Figure 2), and has been expanded yet again for the current run, which began in 2023. At the present time, sketchy information is now being kept for a significant fraction of the bunch crossings for which the Level-1 trigger says “yes” but the High-Level trigger says “no”.

Figure 2: CMS’s own version of Fig. 1 as appropriate for the 2018 data taking period. Note the faster data rates compared to Fig. 1. (“Hz” = “per second”, “kHz” = “1000 per second”, “MHz” = “million per second”.) Taken from https://arxiv.org/abs/2403.16134 .

After CMS demonstrated this approach could work, ATLAS developed a parallel program. Separately, the LHCb experiment, which works somewhat differently, has introduced their own methods; but that’s a story for another day.

Dropping Down a Level

Seeing this, it’s natural to ask: if scouting works for the bunch crossings where the high-level trigger swipes left, might it work even when the level-1 trigger swipes left? A reasonable person might well think this is going too far. The information produced by the level-1 trigger as it makes its decision is far more limited and crude than that produced by the HLT, and so one could hardly imagine that anything useful could be done with it.

But that’s what people said the last time, and so the bold are again taking the risk of being called foolhardy. And they are breathtakingly courageous. Trying to do this “level-1 scouting” is frighteningly hard for numerous reasons, among them the following:

• The number of “no” votes by the level-1 trigger is tens of millions of bunch crossings per second, and thus many trillions per year; even with the data highly compressed, that’s an enormous amount of data to try to work with.
• The level-1 trigger has to make its decision so quickly that it has to take all sorts of shortcuts as it makes its calculations.
• The level-1 trigger only has access to certain parts of the full CMS detector, and only to a small fraction of the data produced by those parts. For instance, it currently has no information from the “tracker”, the part of the detector that is crucial for reconstructing particles’ tracks — though this will change in the future.

So what comes out of the level-1 trigger “no” votes is a gigantic amount of very sketchy information. Having more data is good when the data is high quality. Here, however, we are talking about an immense but relatively low-quality data set. There’s a risk of “garbage in, garbage out.”

Nevertheless, this “level-1 scouting” is already underway at CMS, as of last year, and attempts are being made to use it and improve it. These are early days, and only a few new measurements with the data from the current run, which lasts through 2026, are likely. But starting in 2029, when the upgraded LHC begins to produce data at an even higher rate — with the same number of bunch crossings, but four to five times as many proton-proton collisions per crossing — the upgraded level-1 trigger will then have access to a portion of the tracker’s data, allowing it to reconstruct particle tracks. Along with other improvements to the trigger and the detector, this will greatly enhance the depth and quality of the information produced by the level-1 trigger system, with the potential to make level-1 scouting much more valuable.

Figure 3: The data flow at CMS as of 2023, with Level-1 scouting added. The data rate for Level-1 scouting isn’t shown, because I don’t know it, but it is comparable to the input rate — millions per second. Comparing with Figs. 1 and 2, notice that many other rates are higher than in 2011 and 2018, thanks to improvements in technology and design.

And so there are obvious questions, as we look ahead to 2029:

• What information might practically and usefully be stored from the level-1 trigger when it says “no” to a bunch-crossing?
• What important measurements or searches for new phenomena might be carried out using that information?

My task, in the run up to this workshop, was to prepare a talk addressing the second question, which required me to understand, as best I could, the answer to the first. Unfortunately the questions are circular. Only with the answer to the second question is it clear how best to approach the first one, because the decision about how much to spend in personnel-time, technical resources and money depends on how much physics one can potentially learn from that expenditure. And so the only thing I could do in my talk was make tentative suggestions, hoping thereby to start a conversation between experimenters and theorists that will continue for some time to come.

Will an effort to store all this information actually lead to measurements and searches that can’t be done any other way? It seems likely that the answer is “yes”, though it’s not yet clear if the answer is “yes — many”. But I’m sure the effort will be useful. At worst, the experimenters will find new ways to exploit the level-1 trigger system, leading to improvements in standard triggering and high-level scouting, and allowing the retention of new classes of potentially interesting data. The result will be new opportunities for LHC data to teach us about unexpected phenomena both within and potentially beyond the Standard Model.

It’s been quite a week… Spectacular northern lights for hours on Thursday night. A great comet in the evening skies (though so far I’ve have only caught glimpses, thanks to atrocious viewing conditions.) And now, I’m at CERN (the pan-European particle physics laboratory) for the first time since the pandemic began. I’ll be giving a talk at a conference of CMS experimenters. (CMS and ATLAS are the two general purpose experiments at the Large Hadron Collider [LHC].)

The topic of the workshop is a novel technique called “Level-1 Scouting” — though it isn’t really about “scouting” for anything. It has to do with evading the strait-jacket of the trigger, an essential feature of data gathering at each of the LHC experiments. With tens of millions of collisions per second, the data flood at CMS is too great, and only a tiny fraction of these collisions can be stored. The trigger decides real-time which ones to keep and which ones to discard forever. That’s been the basic rule since the LHC began running.

But this rule no longer applies, thanks to new technology and human ingenuity. CMS now uses level-1 scouting to record sketchy information about every single collision that happens in their detector. LHCb, with a smaller detector, was the first to try something along these lines. ATLAS is on a parallel track. These developments have the potential, looking ahead, to substantially enhance the capability of these detectors. More about this after I’ve given my talk.

Auroras after sunset. (These were as bright to the naked eye) Comet A3 after sunset. (Brighter than to the naked eye.)

Post-sunset light over CERN. (As to the naked eye.)

I hope many of you saw auroras (northern lights) last night! I briefly saw the strongest steady red glow I myself have ever observed, visible even amid street lights and my neighbors’ house lights.

The skies, shown only slightly brighter than to the naked eye, as seen at 8pm Boston time. Credit: Matt Strassler

Then, after a break as some clouds rolled in, we were graced with a few hours of mostly diffuse green glow with patches of dim but distinct red that would come and go. All these colors were visible with the naked eye, albeit much less bright than shown in photos. It was quite a storm, not as violently active as the one earlier this year, but very persistent.

The storm lasted all night, though the auroras varied greatly in brightness. Data from https://www.swpc.noaa.gov/

I also tried to find Comet A3 just after sunset, but failed, even with the help of binoculars. Apparently the brief spike in its brightness, due to “forward scattering” as it passed between us and the Sun, may have died off too quickly, leaving it impossible to see in early twilight. It will become dimmer day by day, but it will also be visible later each evening, and at some point should become easy to see in dark skies. Let me know when you first observe it!

It could be quite a night!

A powerful solar flare (an explosion on the Sun) about 36 hours ago created a large and fast coronal mass ejection (a cloud of subatomic particles heading away from the Sun) that is due to arrive at Earth in the next few hours (it will show up less than an hour before it arrives as chaos in this data.) UPDATE: IT HAS ARRIVED; IF IT’S DARK WHERE YOU ARE, GO LOOK. That could mean problems for the electrical grid. It could also mean strong auroras (northern and southern lights) far from the poles. The timing, if correctly predicted, is such that Asia and Europe may have the best chances, but the auroras could potentially last until it is dark in the Americas too.

Also, just after sunset tonight, we may with difficulty be able to see Comet A3 (short for Comet C/2023 A3 Tsuchinshan-ATLAS ). The comet is bright — some reports give it a brightness comparable to the planet Venus, although more diffuse — but so is twilight. UPDATE: I HAVE BEEN WARNED THAT THE RAPID BRIGHTNING PERIOD, DUE TO A LIGHT SCATTERING EFFECT, MAY ALREADY BE OVER. IF SO, THE STATEMENTS HERE MAY BE TOO OPTIMISTIC. The comet is roughly ten Sun-widths above and slightly to the right of the Sun, and should be visible 15-30 minutes after sunset if you have a low and mostly cloudless horizon. Best bet is to bring binoculars and scan the sky; you’ll notice it much more easily, even if it is visible to the naked eye.

Each day following, the comet will be higher in the sky at sunset, making it more visible in late twilight, but it will also become intrinsically dimmer. Experts seem to disagree about when it will be at its best, but this weekend should be good, if not before.

A busy news week: a Nobel prize, another chance of auroras, and… a comet. It’s probably not the comet of the century, but comets like this one show up only about once every ten years. This one has already been visible in early morning skies. This week it enters our evening skies, and will likely be a lovely sight after dark for the rest of October.

Thursday, Friday and Saturday this week, immediately after sunset and just to the right and above the Sun, comet A3 MAY be at its most spectacular. BE READY! You will need a low and rather flat horizon, and you have less than an hour to see it before it sets, too.

Day by day, the comet will move up and to the left, beginning at the Sun’s right. Look there once the Sun is significantly below the true horizon and the sky has darkened a bit.

Later in the month it will be visible longer into the evening, but much less bright.

What is a comet? Its core (or “nucleus”) is a large ball of ice and dust, perhaps 20 miles [40 kilometers] across, traveling on an orbit of the Sun and moving through the solar system among the planets. That core is far too small and far away to see. But when the comet approaches the Sun, the Sun heats the core, which throws off dust and gas that is blown by the solar wind into a big cloud around the core and into huge trails that stretch tens of millions of miles [km]. These trails reflect sunlight, and can be seen from Earth despite being millions of miles [km] away.

Please do not confuse this comet with Earth’s temporary second moon, which has gotten a ridiculous amount of overheated press, causing both distraction and confusion. Here’s how this itty-bitty “moonlet” compares with comet A3.

• Moonlet temporarily orbits Earth; comet A3 orbits the Sun
• Moonlet is a rock the size of a bus; comet A3’s core is the size of a big city, and its tails are tens of millions of miles long
• Moonlet at its closest will be tens of thousands of miles [km] away; comet A3 at its closest will be 44 million miles [71 million km] away
• Moonlet can only be seen with powerful professional telescopes; comet A3’s head and tails may be dramatic to the naked eye and may even be visible, for a few days, during daylight

The last bullet point is the most important. Moonlet is of intellectual interest only; there’s absolutely nothing to see, despite the crazed news stories in the media. Comet A3 might turn out to be one of the better celestial objects to see in a lifetime. Get the word out!

Quick note: two powerful solar flares occurred in the last 72 hours, creating high spikes in the rate of X-rays from the Sun.

Each flare created a coronal mass ejection that could arrive in a couple of days at Earth, potentially creating a geomagnetic storm. Consequently there’s a good probability this weekend, especially Saturday night into Sunday morning (in Europe and the US), of seeing northern and southern lights (auroras). [See this post for some advice as to how to infer whether the storms have started and/or are ongoing.]

This is my second post on the subject of why “the speed of light (in empty space)”, more accurately referred to as “the cosmic speed limit”, is so fast. This speed, denoted c, is about 186,000 miles (300,000 km) per second, which does indeed seem quick.

But as I pointed out in my first post on this subject, this isn’t really the right question, because it implicitly views humans as centrally important and asks why the cosmos as strange. That’s backward. We should instead ask why we ourselves are so slow. Not only does this honor the cosmos properly, making it clear that it is humans that are the oddballs here, this way of asking the question leads us to the answer.

And the answer is this: ordinary atomic material, from which we are made, is fragile. If a living creature were to move (relative to the objects around it) at speeds anywhere close to c, it couldn’t possibly survive its first slip and fall, or its first absent-minded collision with a door frame.

Today I’ll use a principled argument, founded on basic particle physics and its implications for atomic physics, to show that any living creature made from atoms will inevitably view the cosmic speed limit as extremely fast compared to the speeds that it ordinarily experiences.

In the next post I’ll try to go further, and suggest that we must travel at even slower speeds. However, doing so becomes increasingly difficult. We potentially have to get into details of materials, of chemistry, of biology real and imagined, and of the specifics of the Earth. Once we enter this territory, the issues become complex, the logic and conclusions may be debatable, and I’m no longer expert enough to be sure I know what I’m doing. Perhaps readers can help me with that stage when we get to it.

By contrast, the logic presented here today is straightforward and impossible to evade. Along the way it will also teach us why nuclear weapons are so terrifying — why the energy hidden inside atomic nuclei is so much larger than the energies we encounter in our daily activities.

There are a lot of elements to the reasoning, so what I’ll give here is an overall sketch. But you’ll find many more details in the hyperlinks to other pages, some on this website and some beyond.

All Atomic Creatures Will View “c” As Fast

The argument is based on two simple observations about atoms, which I’ll combine in two ways to derive facts about energy and speed. All numbers given below will be very approximate, because we don’t need precision to draw the general conclusion, and trying to be more precise would make the argument longer without making it clearer. (See chapter 6.1 of my book for a discussion of physicists’ “rules of precision”.)

1. The Electromagnetic Force Makes Atoms’ Outer Electrons Slow

The electromagnetic force is a moderately weak force by particle physics standards (despite being much stronger than gravity). It has only about 1% of the strength of what we’d consider a reasonably strong force. As a direct result, the electron in a hydrogen atom moves around the atom at a speed v that is far below c — approximately 1% of c. (See also this article and this article.)

The electrons on the very outer edge of any atom (the “valence electrons”) are affected by an attractive electric force from the positively charged nucleus, but are also repelled by the electric force from all the inner electrons, which have negative charge. The net effect is that positive charge of the nucleus is substantially shielded by the negative charge of the electrons, and the resulting force on the valence electrons is not dramatically different from that found in a hydrogen atom. As a result, these valence electrons are somewhat similar to the one electron in hydrogen, and so they too move around at about 1% of c, typically a bit slower. (This “1%” is very imprecise, but it’s never as small as 0.1%.)

Thus for any atom, the outer electrons have

Here the “~” sign means “is very roughly equal to,” indicating purposeful imprecision. From this we can estimate the typical energy required to disrupt the atom — the “first ionization energy“. That energy is the combination of

• the valence electron’s motion energy 1/2 mv2 and
• the “binding energy” that holds that electron to the atom.

The motion energy and binding energy are similar in size. (This is always true for any force that decreases as 1/(distance-squared), including electric and gravitational forces.) As a result, the first ionization energy is close to the valence electron’s motion energy 1/2 mv2. Just as for a hydrogen atom, this energy is always about 1/10000th, or 0.01%, of the internal E=mc2 energy of an electron. In math terms, the fact that v/c ~ 0.01 for a typical valence electron implies that the ionization energy divided by the electron’s internal energy is roughly

Let me just emphasize again that I’m not being precise because precision isn’t needed for this argument.

Aside: Those of you who know a little quantum physics know that v isn’t really defined for an electron, because it’s a wavicle, not a particle, and that electrons don’t really go around their nuclei in orbits, despite the picture of an atom that’s so often drawn. I’m using Bohr’s cartoon of an atom here, which is enough to get the right estimates for what is going on. But we could do things correctly, and avoid ever writing “v,” by just using the ionization energy all the way through the argument. We’d get the same answer in the end.

2. The Strong Nuclear Force Gives Atoms a Big Mass

An atom has a nucleus at its center, consisting of between 1 and about 300 protons and neutrons. The strong nuclear force forms the protons and neutrons by tightly trapping quarks, anti-quarks and gluons. It then subsequently binds protons and neutrons, somewhat more loosely, into nuclei.

The most common materials, which are forged in the early universe and in ordinary stars, run mainly from hydrogen (1 electron and 1 proton) to iron (26 electrons, 26 protons, and typically 30 neutrons). Since neither hydrogen nor helium is suitable on their own for making life forms, as their chemistry is too simple, it’s reasonable to define a “typical atom” as one with roughly 10 or so protons and neutrons in its nucleus. (Carbon usually has 12, oxygen 16, etc.)

Now we need to take note of three different and unrelated aspects of particle physics.

• The strong nuclear force becomes extremely strong at a distance D that is about 1/100000th of an atom’s diameter. This sets the size of protons and neutrons, and assures they have almost the same mass Mp. That mass, about equal to the mass of a single hydrogen atom, is related to D by the formula Mp ~ h/(cD), where c is the cosmic speed limit and h is Planck’s constant, the mascot of quantum physics.
• The value <H> of the Higgs field corresponds to a mass about 250 times larger than that of a proton,
• The interaction of the Higgs field with electrons is tiny, and characterized by a number called “ye” which is about 1/400000.

Combining the last two tells us the electron’s mass, m ~ ye<H>, is very small compared to the majority of known elementary particles.

Taking all three facts together (which are independent as far as we know [none of them can yet be predicted from first principles]), it turns out that

(More precisely, the proton’s mass is nearly that of 1836 electrons, and the neutron’s 1838; but 2000 is close enough for our current purposes.)

Therefore, for a typical atom with mass M ~ 10 Mp , the ratio of the atom’s mass to the electron’s mass m, which is also the ratio of the energy stored inside that atom to the energy stored inside a single electron, is

Again, this all follows from known facts about subatomic particles. It isn’t something that anyone can explain from scratch, but for our purposes, it’s enough to know that it is true. Let’s see what the consequences are.

3. Atoms with Slow Electrons and a Large Mass are Fragile

Combining sections 1. and 2., let’s compare amount of energy that it takes to pull an outer electron off a typical atom (its first ionization energy), which is approximately equal to the motion-energy 1/2 mv2 of the electron, to the energy Mc2 stored inside that atom:

• 
  
  

Thus the amount of energy needed to disrupt an atom is a minuscule fraction of the energy that it carries inside it. Atoms are very fragile indeed!

This now explains why the energies of ordinary life must be so small compared to the energy stored in objects, and why nuclear weapons can draw on so much more energy than we are used to. If the energy per atom involved in ordinary activities, such as catching a ball or jumping up and down, were any more than a tiny fraction of the energy stored inside an atom, many of our atoms would lose one or more electrons right away, instantly ruining our biochemistry and destroying our internal structure. We can only survive because the energy of ordinary life is tiny compared to what the cosmos considers normal.

4. Fragile Atoms Can’t Survive Fast Collisions

A head-on collision between two typical atoms with mass M, each with speed V, will involve energy 1/2 MV2 for each atom. If this collision energy is comparable to or exceeds the energy needed to disrupt either atom, which is about 1/2 mv2 (where as before m is the mass of an electron and v is the speed of a valence electron in the atom) then at least one of the atoms will probably lose an electron. So to avoid this, it must be that

• 
  
  

where in the second line I used the result from section 3. Taking the square root of this line, we find

Thus atoms cannot survive intact in any collision whose relative speed is comparable to or faster than 0.00005 c — about 10 miles (15 km) per second. In any collision of ordinary objects at such a speed, the collisions of their individual atoms will lead to widespread atomic disruption, leaving the objects seriously damaged.

Aside: as noted, I have been imprecise all throughout this argument. The true maximum speed for the survival of typical atomic materials may be somewhat slower than 0.00005 c — but not too much so. Perhaps a reader can suggest a more precise estimate?

5. Life (and Anything Else) Made From Atoms Must Move Gingerly

Therefore, for living creatures to avoid injuring themselves irreparably at the atomic level every time they stub their toe or accidentally bump in to one another, they must travel slowly. Relative to objects in their environment, they dare not travel faster than 10 miles (15 km) per second at all times — much less than a 1/10000th of the cosmic speed limit.

And therefore, when they first discover the existence of c, they will all, without exception, express surprise and amazement at how fast it is — more than 10000 times faster than the motions of their ordinary existence.

Humans and Tardigrades

Now, of course, you and I are restricted to much slower speeds than 10 miles (15 km) per second! Even a collision at 10 feet (3 meters) per second, about 7 miles (11 km) per hour, will hurt a lot, and speeds ten times that would surely be fatal. For us, c isn’t just 10,000 faster than what we’re used to — it’s about 100,000,000 times faster than jogging speed!

So clearly this argument gives an overestimate of how fast we can go. There must be additional issues that force us to move even more slowly than the speeds that would disrupt atoms. This is true, but those constraints are much more complicated. That’s why I decided to begin with this relatively simple and very general argument.

What’s good about this argument is that it applies to all atomic objects. It restricts not only natural life on Earth but all imaginable atomic life anywhere — even artificial life that we or some other species might potentially create.

Many organisms are far stronger than we are, tardigrades most famously among them. (Note that tardigrades are small, but not microscopic.) We’ve been making robotic machines for quite some time that can survive and thrive in environments that would kill us instantly. Current technology can already create simple artificial life forms.

Nevertheless, no matter how good our technology, and no matter how intricate the unconscious process of evolution, we will never encounter or construct complex objects that can remain intact in environments where relative speeds are as high as 1/10000th of c, unless

• they remain forever isolated in deep space, where collisions with any large objects are extremely unlikely, and collisions with atoms are infrequent enough that the resulting surface damage is manageable [which is why our spacecraft, not to mention asteroids and planets, are able to travel safely much faster than Earthly objects do], or
• we someday find a building block stronger than atoms from which a robot or artificial life form can be built [but given what we know about the universe so far, this may forever remain science fiction.]

Here’s an interesting and relevant piece of information: it has been shown that frozen tardigrades can survive collisions with sand at tremendously higher speeds than we humans can handle, but only up to about 0.6 miles (0.9 km) per second — about 1/300000th of c. (This makes it challenging for them to travel successfully between planets and moons across the solar system, where typical relative speeds of large objects and meteors are in the 10 km/second range.) On the one hand, this shows that at least some life forms can survive much more rapid collisions than we can. On the other, they have limitations that are consistent with today’s reasoning.

Could one could create a intelligent creature of a larger size that could match the durability of a tardigrade? That is perhaps doubtful, but we can discuss that after the next post.

Slow is Better

Thus by combining basic knowledge concerning our universe —

• the moderate weakness of the electromagnetic force,
• the great strength and trapping ability of the strong nuclear force,
• the substantial value of the Higgs field,
• the tiny interaction of the Higgs field with electrons,
• the nature of typical atomic nuclei, and
• the behavior of valence electrons in typical atoms —

we learn that any object made from atoms cannot endure collisions at speeds anywhere close to c. And now we know the reason why the cosmic speed limit seems so fast — and why nuclear weapons seem so violent.

The reason is simple: in this universe, only the slow survive.

I’m often asked two very natural and related questions.

1. Why is the speed of light, usually denoted c, so astonishingly fast?
2. Why, in Einstein’s famous equation relating energy and mass — E=mc2 — does c2, a gargantuan number, appear?

It’s true that the speed of light does seem fast — light can travel from your cell phone to your eyes in a billionth of a second, and in a full second and a half it can travel from the Earth to the Moon.

And indeed the energy stored in your body is comparable to the Earth’s most explosive volcanic eruptions and to the most violent nuclear bombs ever tested — enormously greater than the energy you use to walk across the room or even to lift a heavy suitcase.

What in the name of physics — and chemistry and biology — is responsible for these bewildering features of reality? The answer is fascinating, and originates in particle physics and the resulting structure of matter. It is surprisingly intricate, though, so I’m going to approach this step-by-step over three blog posts. Here’s the first.

Refining and Rephrasing the Questions

We should start by recognizing that the second question has two sub-questions, one qualitative, and one precise:

• 2a. Why, in Einstein’s famous relation between energy E and mass m, does a gargantuan number appear?
• 2b. Why is that gargantuan number equal to the speed of light squared, i.e. c2?

We’ll see that questions 1 and 2a are almost the same question, and have largely the same answer. But as we’ll see, they aren’t phrased well yet.

The problem is that “fast” and “gargantuan” are relative terms. I can run much faster than a slug but much slower than a cheetah. I am huge compared to a bacterium, but not compared to a star. So we ought to start by restating these questions in relative terms; that will help us think them through.

• 1. Why is the speed of light so much faster than the speeds that we humans ordinarily experience?
• 2a. Why is the energy stored in the masses of ordinary objects (via E=mc2) so much larger than the energy of the ordinary processes experienced in daily life?

The Cosmos Has a Viewpoint

To get us warmed up, I’ll start with a brief quote from my book, chapter 2.

“It’s well-known that light has a characteristic speed, which scientists call c ; this is the speed at which each individual photon travels, too. As scientists discovered centuries ago, c is about 186,000 miles per second. That’s fast, in a way. Our fastest spaceships don’t come anywhere close to that speed. Though my last car was with me for fifteen years, I drove it less than 186,000 miles. At the speed c , you could circle the Earth in a blink of an eye (literally) and travel from my head to my toe in a few billionths of a second.

“And yet c is also slow. It takes light more than one second to travel to the Moon, over eight minutes to reach the Sun, and over four years to reach the next-nearest star. If we sent off a robot spaceship at nearly c to explore the Milky Way, it could visit only a few dozen nearby stars during our lifetimes.

“You and I are small, so we think light runs like a rabbit. But the universe is vast, and from its perspective, light creeps like a turtle.”

The point of this quote is to remind us that we’re not the center of the universe. We are not annointed creatures relative to whom all cosmic facts should be measured. There’s nothing unique or special about the Earth or its size, mass or temperature — nothing materially unique about animals, about mammals more specifically, or about us. The way the cosmos works is not influenced by the objects of our ordinary lives. So our own perspectives are not privileged, and we should be aware that there are other perspectives, ones from which light’s speed is slow and/or from which the energy stored in a human is tiny.

To make our questions really meaningful, then, we ought to step back and ask not just how we view the cosmos but how the cosmos views us. From the universe’s perspective, the questions really are these:

• 1. Why are humans so astonishingly slow compared to the natural speeds of the cosmos?
• 2a. Why are the energies involved in ordinary human affairs so insanely tiny compared to the natural energies one would expect from objects of human scale?

For us to understand how the universe would answer these questions, we have to understand what “natural speed” and “natural energy” might mean from a cosmic perspective. So let’s start there.

The Natural Speed

The quantity c is not just the speed of light, and so “speed of light” is not the best name for it. For instance, it is also the speed of gravitational waves. Even more important, it is the limit on the relative speed of all physical objects. That’s why I and many others often call it “the cosmic speed limit” — because that makes it clear that rather than being a property of light, it is a property of the universe. (Caution; there are lots of conceptual traps and subtleties here, some of which I’ve written about.)

This cosmic speed limit seems to be the same everywhere across the universe (based on our observations of almost unimaginably distant and ancient objects), and so every living intelligent creature in the cosmos can measure it. No other speeds are fixed and reliable in the same way. Compare it, for instance, with the speed of sound. Sound speed varies with temperature and with the material through which it travels, and so this speed is completely different in other planets’ atmospheres and oceans. It could never be used as a cosmic measure of speed that all intelligent species could agree on.

Nor should we think of human speeds of about 1 meter per second (about one yard per second) as “normal speed”. First, if we were peregrine falcons or sloths, we’d view human speed very differently. Second, the now-standard choice of “meter” to measure length and “second” to measure time is arbitrary. A blue whale is many meters long, very big in this sense. But a sufficiently intelligent species of whale wouldn’t use “meter” as their yardstick, and would instead likely define length using a “whaler”, comparable in size to a whale. We’d be a fraction of a whaler tall, and thus seem diminutive by that measure. Similarly, a sequoia tree would probably not want to use “second” as a time-frame; “hour” would be more characteristic.

So the precise way one defines distances and times and speeds, and what makes a length or a duration or a velocity large or small, are all species-dependent, planet-dependent, and perspective-dependent unless you use facts about the cosmos that everyone can agree on. And when it comes to speed, the cosmos has a view on this matter. It says:

“c is normal speed, because that’s the maximum rate at which information can travel from one place to another. No two objects can move relative to each other faster than that. No knowledge can be sent faster than that. There’s no other speed of comparable stability or of comparable importance. So typical objects should always pass each other at a speed that is a reasonable fraction of c.

“But, uhhh… WOW… you Earth-creatures are absurdly, ridiculously slow! Look at how you crawl around your planet!”

The Appearance of c2

Setting aside the issue of whether c should be viewed as large, small or normal, why is it “natural” that the energy E stored inside an object should be related to its mass m by c2? My answer follows the logic of this post, which goes into more detail about the methods of “dimensional analysis”, one of physicists’ most important tools. You may want to read it if my explanation here seems too sketchy to you.

Einstein’s basic claim was that even a stationary object has energy stored inside it. The amount of that energy, he suggested, is reflected in its mass — specifically its “rest mass” m, which is the mass as measured by an observer who is stationary relative to the object. (For more details on rest mass and on various forms of energy, see chapters 5-8 of my book.)

Any relation between energy and mass must involve the square of a speed (or the product of two speeds.) We find this already in first-year physics. In pre-Einsteinian days, the motion energy (i.e. “kinetic energy”) of a moving object was understood to be equal to an object’s mass m times its speed v squared:

• Newtonian-era motion energy = 1/2 mv2

If you tried to replace v2 with v3 or v99 , the equation would become nonsensical. (As a physicist would say it: the units on the two sides of the equation don’t match.) It would be like claiming that the height of a tree is equal to the color of its leaves — two things of completely different character can’t generally be equal.

But back to Einstein’s claim that a stationary object has energy too. The corresponding formula can’t contain v, since a stationary object has v=0. Some other speed or speeds must appear instead.

Why should that speed be c? Well, it wouldn’t make much sense for an object’s energy/mass relation to depend on the speed of some other object. Imagine if the energy in my body were my mass times the square of the speed of some ultra-distant star. Not only would this be bizarre (and inconsistent even with Galileo’s relativity), what would the formula have meant before the star was born?

No, the relationship between energy and mass for stationary objects must be universal — cosmic — and so it can only depend on speeds that are properties of the universe itself. As far as we know, the universe has only one inherent speed: c. (In fact you can prove that Einstein’s conception of relativity would be inconsistent if there were more than one basic speed.) Therefore any relation between energy and mass must be of the form E = #mc2, where # is a fixed number that someone has to figure out. There’s no other equation that could logically make any sense.

Einstein knew this, of course, even before he wrote his relativity papers. So did all his colleagues.

The fact that the # is equal to 1 is partly a historical accident of definitions, and partly, given this accident, a matter of brilliant deduction and imagination. Click here for some details.

Regarding the question as to whether E = 1/2 mc2 or E = 2 mc2 or E = 4/3 mc2, here physicists got a little lucky historically. The definition of mass was given in Newton’s day, and energy was defined later in just such as a way that, for pre-Einsteinian physics, the motion energy of a moving object is 1/2 mv2. There are sensible reasons for that definition. It is directly related to the definition of momentum as mv, mass times velocity, with no 1/2 or 2 in front. The definition of momentum was in turn was motivated by Newton’s equation F=ma, which defines what we mean by mass. If Newton had put a 1/2 in that equation, defining mass differently, then there’d be a 1/2 in Einstein’s formula too. But with the definitions that Newton and his followers used, the correct equation that matches nature is E=mc2 , with no numerical factor. That’s a nice historical accident; any change in the definition of energy or mass would have affected the sleek appearance of Einstein’s formula.

Now, why was Einstein the one to figure out that, with these definitions, the correct number in the equation is 1, when his colleagues had been trying so hard and getting so close for a couple of decades? He asked the right question, while his colleagues did not. More about that here.

So 2b is answered: in our universe, the only possible relation between E and m for a stationary object is E=#mc2, where # may depend on how one’s culture exactly defines energy and mass, but which happens, with our historical definitions of energy and mass, to be 1.

The Natural Energy

And so, from the universe’s perspective,

“The natural energy for an object with a rest mass m is something like mc2 . When the object is stationary, that’s exactly how much energy it has, and when it’s moving, it has more. And if it’s moving at a natural speed — some moderate fraction of c — then we already know from pre-Einstein physics that its motion energy will be something like 1/2 mv2 , which will be a substantial fraction of mc2 . In short, typical objects in the universe will be seen to carry internal energy mc2 and motion energy which is not so far from mc2.

“But you Earth-creatures … you are like frightened mice, keeping all your activities down to a tiptoe and a whisper! Are you trying to avoid being noticed? Are you cowards, afraid of any drama?”

The answer to the last question is “yes, absolutely”. But more on that in the next post.

Why the Energy Question is a Speed Question

I’ve already now hinted at why the energy question 2a is the same as the speed question 1. The reason the energy stored in ordinary objects seems so large in human terms is that the speed of light seems so fast in human terms.

Again,

• Einstein claimed (and it was soon confirmed in experiments) that a stationary object has internal energy mc2, where m is called the “rest mass” of the object.
• For slow objects like us, with v much less than c, we can use Newton’s approximations to Einstein’s equations, for which an object of rest mass m moving at speed v has motion energy 1/2 mv2.

This means that the ratio of an object’s motion energy, which is easily observed in ordinary life, to its internal energy, which is hidden in ordinary life, is

• (motion energy)/(internal energy) = (1/2 mv2 ) / (mc2) = 1/2 (v/c)2

This is extremely tiny if (v/c) itself is very small. And therefore, if we understand why v is so much less than c in daily life, then we will simultaneously understand why the energies of ordinary human affairs are so small compared to the internal energies of typical objects around us.

So when I return to this topic in an upcoming blog post, we’ll explore why particle physics itself assures that the speeds of daily life must be slow.

Stay tuned for the next post in this series!

My hour-long conversation with UCSD Professor Brian Keating, on his Into the Impossible podcast, has just come out on YouTube; click here to listen.

We covered several topics from my book, including what particles really are and how the Higgs field gives them mass, along with others ranging from renormalization to the nature of the book’s cover.

The podcast’s intro sequence is a bit wild — a mix of Dr. Who meets the Discovery Channel — but hang tight, because the discussion itself is serious science. One thing that’s fun about it is that Keating asked me a number of questions that no one had asked me on prior podcasts that I’ve been on. The fact that some of his queries were a bit “out there” adds to the entertainment value. I think you’ll enjoy it.

As a reminder, I have a number of other podcasts and interviews that you can choose from, listed below:

• Shalaj Lawania’s podcast “Know Time”
  • Episode title: “Particle Physics, Waves & the Higgs Field”
    • 185 minutes (!!), covering all the main topics in the book and some metatopics too
      
• The “Quirks and Quarks” show:
  • Episode title: “Why an essential subatomic particle plays the field”
    • 15 minutes, on how the Higgs field gives mass to particles
      
• Sean Carroll’s podcast “Mindscape”
  • Episode title: “Matt Strassler on Relativity, Fields, and the Language of Reality”
    • 90 minutes, all about the book
      
• Daniel Whiteson’s podcast “Daniel and Jorge Explain the Universe”,
  • Episode title: “Is the Universe Made From Waves?”
    • Part 1 , 43 minutes
    • Part 2 , 53 minutes
      

I’m very pleased to report that “Waves in an Impossible Sea“, my book about the universe and its secret role in every aspect of daily life, has been selected by the Wall Street Journal as one of “10 Books to Read Now: Science and Technology”.

The full list and the reviews are behind a paywall, but you can see the titles of the books even before the paywall. The other nine are:

• Supremacy, by Parmy Olson
• Escape from Shadow Physics, by Adam Forrest Kay
• Putting Ourselves Back in the Equation, by George Musser
• Count Down, by Sarah Scoles
• Magic Pill, by Johann Hari
• Superconvergence, by Jamie Metzl
• The Afterlife of Data, by Carl Öhman
• Read Dead’s History, by Tore C. Olsson
• Who Wrote This, by Naomi S. Baron

Ten books to keep our minds active and up-to-date! We all have some reading to do…

What? There’s a comet coming?

In fact, it’s already here. Oh yes, it seems that 2024 may not just be the year of a terrific solar eclipse and spectacular outbursts of northern lights (and maybe, just maybe, a nova.) In morning twilight, if you live in the right latitudes, an ever-brightening comet can apparently be spotted right now. I haven’t seen it yet, but I’m hoping to get a chance.

Nothing in cometary life is guaranteed; comets can fall apart unexpectedly, or fail to brighten as expected. So far, though, Comet C/2023 A3 Tsuchinshan-ATLAS is looking promising; its tail may soon be longer than its name.

The comet will soon be seen in the evening sky. But for the next few days, it is visible in the morning sky during the last hour before sunrise. Depending on

• which day it is — the comet moves noticeably across the sky from one day to the next — and
• your latitude — close to the equator is better, and slightly south of the equator is best —

you may have an opportunity to find it. It will not be easy, as it will be close to where the Sun is soon to rise, and it is not bright enough to shine easily through the morning twilight. (Perhaps binoculars would help; I’m not sure.) But I have seen a photograph, so it can be found, with some effort.

You will definitely need a very low and clear horizon to see it this week. To get a sense of how high it might be above an ideal, unencumbered horizon, look at this informative chart made by Nick James (British Astronomical Association) and posted at spaceweather.com. It shows the comet’s altitude in degrees above the horizon, about 20 minutes before sunrise, for various latitudes (as labeled in the upper left corner; “+” means north, “-” means south), for each day over the next two weeks or so. In the US, you are best off in the next couple of days, and your chances are better you’re in the southern half of the country, around 30-35 degrees latitude or less. Much of northern Europe is probably out of luck for now. Over the coming few days, Africa, South and Central America, Australia and southern Asia should have the best views. Then the comet leaves the morning sky.

The comet may well be more easily and more conveniently visible in mid-October’s evening sky, so consider this the first but perhaps not the only opportunity to see it. Let me know if you manage to spot it this week!

As promised, the audiobook for Waves in an Impossible Sea, read by Christopher Grove, has finally come available. You can find it on Audible and on many other platforms. (Click here to order the audibook, hardback, or e-book.)

To help make the text easier to follow, I’ve put the 50+ figures, the 6 tables, and the glossary on-line. You might, for instance, choose to have them open on your phone for easy reference while you’re listening. (The endnotes are also there too, although my understanding is that Mr. Grove won’t be mentioning them as he reads, so you may need the text to make them useful.)

There are additional resources for readers already up on this website, supplementing the book, and more are coming soon, so please make use of them. Also feel free to ask me questions if you find yourself confused — and please don’t be embarrassed to do so, because the universe is confusing… even to physicists. No question is too simple; in fact, the simple ones (what is empty space? what’s a particle? why don’t we feel the Earth’s motion?) are often the hardest to answer.

Things have been extremely busy! I have

• written a new article for New Scientist about the familiar-sounding words that we use in physics (such as “particle”) and how they can easily mislead the unwary;
• appeared in an extended Know Time podcast, hosted by a non-scientist, in which we discuss fields, particles and the Higgs boson — core material of my book Waves in an Impossible Sea; and
• learned that the audiobook version of the book is now available for pre-order; it comes out September 24th. 

If any of these might interest you, here are the details!

Article on Science and Language in New Scientist

First, about the latest article I’ve written for New Scientist magazine. (My other New Scientist articles can be found at the bottom of this page.) This one is about the interplay between science and language. There are a lot of words in English that have been repurposed by physicists — force, mass, energy, field, etc. — whose meanings for physicists differ, to a greater or lesser extent, from their meanings in ordinary conversational settings.  This definitional mismatch creates all sorts of opportunities for misunderstandings.

I also dealt with this issue, to a certain extent, in my book. From my experience teaching, and also writing on this blog for many years, I have come to the conclusion that one can’t properly explain the most important results of modern physics without close attention to this linguistic challenge. 

Anyway, in this new article, the focus is mostly on three words crucial for modern physics: atom, force, and particle.  I examine how and why their meanings have shifted over time, and the legacies of these shifts for those trying to make sense of physicists’ verbal explanations of how the universe works.

This is my second article of the month; if you missed my article in Quanta Magazine about how the Higgs field truly gives mass to elementary particles, you can find it here.  My approach to this topic (also covered extensively in my book) avoids the false analogies of the Higgs field being like molasses, or soup, or anything else that violates the Principle of Relativity. It also draws attention to the connection of these ideas to those of resonance, which is fundamental to the physics of musical instruments.  

If you find these articles too brief or too oracular, the book can provide far more details without the use of math.  If you actually want some of the math (but not too much), you can find that here on this website, for example here and here. If that’s still not quite what you want, feel free to ask me for guidance, or explore this website further using the Search bar at the upper right of this page.

Know Time Podcast About the Topics of my Book

Shalaj Lawania, on his podcast Know Time, has a terrific series of interviews with a wide variety of interesting people, including but not limited to scientists.   I’m very pleased to be added to his impressive list. It’s a real shame that he has relatively few subscribers, given the high quality of what he is doing. I strongly encourage you to check out his channel.  You will not be disappointed.

As he always does, Lawania curated a well-structured interview. We methodically covered a wide range of topics from my book, as well as some more general issues about science and belief.  The full interview is two hours long!  But no worries if that’s way too much; you can listen to various self-contained excerpts that Lawania has separated out.

The AudioBook is Finally In Sight

Since many people find it convenient to listen to books rather than read their texts, it’s not surprising that I’ve often been asked about the audio version of my book, for which we’ve had to wait over six months. But the wait is over. I’m pleased to tell you that the audiobook will finally become available next Tuesday, September 24th.  (It can be pre-ordered now.) The company who recorded it wanted a professional reader with an in-house recording studio, so they did not offer me the option of reading it myself. But I am reasonably confident in the skills of the reader they selected.

I’m concerned, though, that the audiobook may be harder to follow than the written text. After all, the written text has many figures and a glossary, and it’s more amenable when one wants to review earlier material that appears again in a later section. To mitigate this, I have put the figures, the tables, the glossary, and the endnotes online on this webpage. That way, while you’re listening to the audiobook, you can have the images etc. open in your browser, so that you can access them easily when they are mentioned. 

And I do think you should expect to listen to certain sections of the book twice. The ideas of modern physics are very strange indeed. I’m sure that I myself, before I took physics classes, would have had trouble completely absorbing these concepts the first time through.

Let me know how the audiobook works for you! And if you think there’s anything I can do on this website to make the audiobook easier and more accessible, please let me know.

More to Come

More podcasts and articles are in the works. So is additional supporting material for the book. Stay tuned!

Back in April 2022, the CDF experiment, which operated at the long-ago-closed Tevatron particle collider. presented the world’s most precise measurement of the mass of the particle known as the “W boson“. Their result generated some excited commentary, because it disagreed by 0.1% with the prediction of the Standard Model of particle physics. Even though the mismatch was tiny, it was significant, because the CDF measurement was so exceptionally precise. Any disagreement of such high significance would imply that something has to give: either the Standard Model is missing something, or the CDF measurement is incorrect.

Like most of my colleagues, I was more than a little skeptical about CDF’s measurement. This was partly because it disagreed with the average of earlier, less precise measurements, but mainly because of the measurement’s extreme challenges. To quote a commentary that I wrote at the time,

• “A natural and persistent question has been: “How likely do you think it is that this W boson mass result is wrong?” Obviously I can’t put a number on it, but I’d say the chance that it’s wrong is substantial. Why? This measurement, which took several many years of work, is probably among the most difficult ever performed in particle physics. Only first-rate physicists with complete dedication to the task could attempt it, carry it out, convince their many colleagues on the CDF experiment that they’d done it right, and get it through external peer review into Science magazine. But even first-rate physicists can get a measurement like this one wrong. The tiniest of subtle mistakes will undo it.”

In the weeks following CDF’s announcement, I attended a detailed presentation about the measurement. The physicist who gave it tried to convince us that everything in the measurement had been checked, cross-checked, and understood. However, I did not find the presentation exceptionally persuasive, so my confidence in it did not increase.

But so what? It doesn’t matter what I think. All a theorist like me can do, seeing a measurement like this, is check to see if it is logically possible and conceptually reasonable for the W boson mass to shift slightly without messing up other existing measurements. And it is.

(In showing this is true, I took the opportunity to explain more about how the Standard Model works, and specifically how the W boson’s mass arises from simple math, before showing how the mass could be shifted upwards. Some of you may still find these technical details interesting, even though the original motivation for this series of articles is no longer what it was.)

Instead, what really matters is for other experimental physicists to make the same measurement, to see if they get the same answer as CDF or not. Because of the intricacy of the measurement, this was far easier said than done. But it has now happened.

In the past year, the ATLAS collaboration at the Large Hadron Collider [LHC] presented a new W boson mass measurement consistent with the Standard Model. But because their uncertainties were 60% larger than CDF’s result, it didn’t entirely settle the issue.

Now the CMS collaboration, ATLAS’s competitor at the LHC, has presented their measurement. They have managed to be almost as precise at that of CDF — a truly impressive achievement. And what do they find? Their result, in red below, is fully consistent with the Standard Model, shown as the vertical grey band, and with ATLAS, the bar line just above the red one. The CDF measurement is the bar outlying to the right; it is the only one in disagreement with the Standard Model.

Measurements of the W boson mass made by several different experiments, with names listed at left. In each case, the dot represents the measurement and the horizontal band represents its uncertainty. The vertical grey band represents the Standard Model prediction and its own uncertainty. The ATLAS and CMS measurements, shown at the bottom, agree with each other and with the Standard Model, while both disagree with the CDF measurement. Note that the uncertainty in the CMS measurement is about the same as in the CDF measurement.

Since the ATLAS and CMS results are both consistent with all other previous measurements as well as with the Standard Model, and since CMS has even reached the same level of uncertainty obtained by CDF, this makes CDF by far the outlier, as you can see above. The tentative but reasonable conclusion is that the CDF measurement is not correct.

Of course, the CDF experimentalists may argue that it is ATLAS and CMS that have made an error, not CDF. One shouldn’t instantly dismiss that out of hand. It’s worth remembering that ATLAS and CMS use the same accelerator to gather their data, and might have used similar logic in the design of their analysis, so it’s not completely impossible for them to have made correlated mistakes. Still, this is far from plausible, so the onus will be on CDF to directly pinpoint an error in their competitors’ work.

Even if the mistake is CDF’s, it’s worth noting that we still have no idea what exactly it might have been. A long chain of measurements and calibrations are required to determine the W boson mass at this level of precision (about one part in ten thousand). It would be great if the error within this chain could be tracked down, but no one may have the stamina to do that, and it is possible that we will never know what went wrong.

But the bottom line is that the discrepancy suggested by the CDF measurement was always a long shot. I don’t think many particle physicists are surprised to see its plausibility fading away.

2ND UPDATE: Auroras are indeed being observed. (I myself am a bit too far south and skies are hazy, making the moonlight blinding; but I am reading reports from northern Europe.)

UPDATE: Something has happened at the ACE satellite around 2300 UTC (0100 Europe time, 7 pm New York time. See the plot added to the bottom of this post.

———-

Still waiting for a possible outbreak of auroras (northern/southern lights) tonight; a tremendous blast from the Sun, launched from a sunspot two days ago, is believed likely to make a glancing impact on the Earth, and to do so within the next 12 hours or so. That means a possibility of bright northern lights tonight if you’re north of, say, New York City’s latitude.

BUT always keep in mind that forecasting auroras is part science, part art, part luck. Our chances are decent, but the forecast can always be wrong.

As far as timing, the best way to monitor what’s going on, I’ve found, is to use https://www.swpc.noaa.gov/products/ace-real-time-solar-wind and look for sudden activity in multiple data channels. If that happens, then the ACE satellite (about a million miles away) has detected a sudden change in the solar wind, and a geomagnetic storm is likely to start at Earth within an hour or so.

Whether you will see auroras or not during the storm depends on how powerful it is, which determines how far from the poles the auroras will reach and how bright they will be. While the forecast is for a strong storm, we’ll just have to see…

At 2300 UTC (about one hour before this posting) you can see jumps occurred in many channels below. That means that the solar storm may begin right around now (0000 UTC, 8 pm New York Time)

I’m delighted to tell you that Quanta Magazine has published an essay I have written on the *real* story of how the Higgs field gives mass to particles — avoiding those famous false analogies. There’s a musical connection, too. I hope you enjoy it! https://www.quantamagazine.org/how-the-higgs-field-actually-gives-mass-to-elementary-particles-20240903/

If you are curious to learn more about the main points of the essay, feel free to ask me questions about it in the comments below or at Quanta Magazine. (I also go into more detail about these subjects in my book.)

Though I’ve been busy with a number of physics and writing tasks, I’ve been beefing up the “Reader Resources” section of this website, devoted to extending the experience of readers of my book. [BTW, the audiobook is due out at the end of September.]

The book has many endnotes (available separately here, in case [like me] you hate paging back and forth between the text and the endnotes, and would like to have the endnotes more easily available on a separate screen.) A number of these endnotes have asterisks, and for those endnotes I promised to provide more information here on this website. Well, that information is going up, step by step.

For example:

In Chapters 1-3, I’ve added information to endnotes that cover a wide range of topics, some historical, some about basic physics, and some on quite advanced subjects (such as how to precisely define the relativity principle [note 1 of chapter 2] and on the cosmic microwave background interplays with the relativity principle [note 1 of chapter 3]).

If any of these topics interest you, click on the relevant chapter heading to go to the webpage that has the added information; or go to the Reader Resources page that has all the chapters. Again, comments are welcome!

• Chapter 1 Overture 1
  • Note 2: On Einstein Quotations
• Part I: Motion
  • Note 2: How to Measure Earth’s Shape and Size
• Chapter 2 Relativity: The Greatest Illusion 15
  • Note 1: Isolated Bubbles
  • Note 2: Earth’s Rotation
  • Note 8: Planes’ Relative Speeds
• Chapter 3 Coasting: Easier Than It Appears 29
  • Note 1: Relativity and the Cosmic Microwave Background
  • Note 3: The Sun and the Earth

. I’m hoping that readers of this blog and of the book will enjoy this new material, and will also let me know if they have questions, corrections, or suggestions as to how I could improve the material further.