Monday 8 January 2018

Q&A On the Status of the Speed of Light

Pi’s New Year Q&A: Is the One-way Speed of Light a Convention?

Martin Cohen and former Pi contributor, Muneeb Faiq explore one of the claimed certainties of physics.

To introduce the issue, here's blogger Burt Jordaan wondering, way back in January 2010, about why the 'speed of light' suddenly became the one true measure of all things scientific.

Burt writes:
'In order to measure any one-way velocity, we essentially need two clocks: one at the start and one at the end. Obviously, the two clocks need to be synchronized and run at the same rate (and to be sure, they must not be moving relative to each other and also be at the same gravitational potential). Let we reasonably assume that the two clocks run at the same rate, at least close enough for all practical purposes. Now we need to synchronize the two clocks to read the same at the same moment. How is this done?'
Recall that Einstein himself clearly admits, in his 1905 paper on Special Relativity, that: "We have not defined a common 'time' for A and B, for the latter cannot be defined at all unless we establish by definition that the 'time' required by light to travel from A to B equals the 'time' it requires to travel from B to A."

Burt says from this that what Einstein terms as being 'by definition' is equally 'by convention'*. Consider: Is the radius of space's curvature related to the speed of light?

The Q&A

Martin: That's a four-guinea question, innit? I believe conventional accounts make space into 'space-time' and the speed of light is allowed to determine things like that, yes.
Muneeb: I don't understand why Einstein established a religion of special abilities and qualities of light. Though there are ways to measure the speed of light but there is no reason to believe that nothing can travel faster. I think a few thought experiments should be propounded to at least break the myth that light owns special physics and light makes nature asymmetric.

There is a lot of confusion about the harmony between the classical and quantum definitions of speed, for example. If both quantum speed and classical speed mean the same then a very interesting difficulty comes to the front. Suppose there exists only one body in the universe. Just a single 'point-mass' and space. Is it at rest or in motion? If, however, there come out two photons of light moving parallel to each other. Now what speed are they moving at? If an observer is stationed on the point-mass, then both the photons are moving with the velocity of light. Yet, suppose, all of a sudden, the point-mass ceases to exist. Now there are only two photons moving with same speed parallel to each other. After all, nothing else exists except space. Before, when the point-mass existed, the two photons were moving with the velocity of light. After, when it has ceased to exist, they seem to not be moving at all! And yet nothing has changed regarding the photons. I hope I have made my point!
Martin: Yes, I get your point... I've wondered about this sort of thing too!

Isn't the usual idea that the universe started with a single point, 'the singularity', and at this time indeed none of the usual laws applied. Then there seems to be a suggestion that the speed of light may not have become 'defined' in the key moments of the first 'explosions'.

Now what this caused me to puzzle a little about, is that if, in fact, the singularity was one particle - as you say, a photon - and if it travels, by definition, at the speed of light, then surely it can be everywhere at the same instant, because of those peculiar Einsteinian laws. In other words, could it be that the universe consists of just one photon, which is everywhere, creating both space and time?

Bear with me! Suppose this is the universe, then why would it matter what speed the photon travelled at, any more than where it was or when? Nothing would be meant by these comparative terms.
What do you think? Can we put our ramblings into a form that would make a suitable webpage? I'd like to try, PI is a good way to organise and explore ideas.
Muneeb: There is an interesting point to note: what are usual laws? Why are they usual? Are the laws of physics really laws in the first place - because if they would really be laws; then they should never fail to explain behaviour of everything that exists. This difficulty hovered around the intellect of many great physicists - including Einstein - and that is why he spent so many years in search of a unified theory that he hoped would explain everything.

Mathematics, theory and philosophy should go hand-in-hand in order to get a further insight into reality. Otherwise we all have to be convinced (like Stephen Hawkings) that there can never be a grand unified theory. But I am afraid in that case, then we have to be convinced that there are no governing laws at all. All physics will melt away.

Instead, let physicists, philosophers and mathematicians come together and work in harmony in an open-hearted, interdisciplinary manner to understand what none of these disciplines will ever be able to get grasp of independently.
Martin:   Well, y'know, this is certainly a good question, but I'm not sure it is quite as clear a distinction as you imply. For example, we might say it is a law of physics that energy can neither be created nor destroyed, no? Without being obliged to throw that principle away just because (eg) some neutrinos evidently don't want to be part of the present theory about cosmic speed limits?
Muneeb:   Yes. You are right. We, of course, can say it is a law of physics that energy can neither be created nor destroyed without being obliged to throw that principle away just because some neutrinos evidently don't want to be part of the present theory about cosmic speed limits. But what is the applicability percentage of these well established laws? If energy and matter can neither be created nor destroyed, then from where did it blast into existence? Shall we then opt for the principle of first cause where these laws fail altogether? No Newtonian law holds good when we discuss atoms and sub-atomic particles. Einstein himself said that quantum mechanics (which is again a set of laws)is not absolute. Furthermore- quantum and classical worlds are composed of same material and, therefore, some basic underlying principles must be obeyed which we have not yet been able to discover. It is not the question of neutrinos only because most of the universe is composed of dark matter and dark energy which was concealed from over imagination for hundreds of years because of the over emphasis paid by physicists on the laws that are collectively described as quantum and classical mechanics.

The portion of the universes that the currently available laws explain is negligible as compared to the great splendour of dark matter and dark energy that fill the universes (previously we concieved only one universe but now we say universes). There may be some "extra-bright matter" and "extra-bright energy" awaiting our discovery. For that, we again have to wait for the failure of currently known laws of physics and those great mathematical equations that terrify all those who are not physicists and mathematicians. Once we fortunately fail, we will be obliged to look for an explanation for the failure and may consequently theorize existence of very weird materials and phenomena faintly conceivable as of now within the delineated perimeters of quantum and classical conditioning. That is why I emphasize on first understanding what makes the universe (what material and quality of materials and types thereof constitute everything), then we need to classify all that material and non material on some sound basis.

We also have to classify on the basis of discovered and not-discovered. Then we have to understand their behaviour. On the basis of the theory generated; we then can develope mathematics which explains things and helps us to imagine what we cant with the help of mere theory. I hope I don't sound insane!
Martin:   Mmmm, absolutely, I do agree that physics is full of 'black holes' to pun little! But I just want us to avoid addressing ill-founded assertions in conventional science with our own ill-founded assertions. For example, the 'dark matter' mystery - is this not a theoretical construct itself, intended to plug an experimental hole in current theory? You speak of it as a discovered reality, but isn't that to fall into the same way of thinking as the people you are critiquing?

Thinking about the 'problem' of where the energy in the universe came from, isn't it perfectly logical to simply say that there is no 'before' to be dealt with or explained?

Over to you, or anyone reading?
Muneeb: Haha! I am caught in a loop.I am not smart enough for arguments. However, though my writing apparently reveals that dark matter is a reality but I don't mean that. That is why I have guessed the existence of extra-bright matter and energy. What I am doing is to use the discoveries of physics to prove the inconsistencies in physics itself.

I should put a caveat here that I am not anti-science or anti physics. Dark matter was discovered by science to plug the black holes (as you say)and may be some other matter and energy will sooner or later be discovered which disproves everything. Does it mean that we should try to adjust our current theories without revising our basic understanding of the universes. Science has made aeroplanes fly etc. but that does not mean science is correct everywhere. Regarding your question of Un-important "before", please allow me to disagree with you because "before" is of great importance.

First question is; what time-point in the evolution of universes is the beginning? Why is a particular scale of past not a "before" and why all of a sudden we think of something as "before"? Cant it be that this "before" may give us inkling into the evolution of the behaviour of everything that apparently exists. What happened before big bang seems to me as important as what happened afterwards. This is because if we come to know the state, status and behaviour of matter, energy, space, time, void etc.before big bang, we will surely get some idea about how matter, space and time evolves to a better extent than if we stop at big bang. Thanks!


Keith said...

The implications of this thought-provoking dialogue — which says it’s “us[ing] the discoveries of physics to prove the inconsistencies of physics itself” — suggest, at the very least, that science is institutionally intransigent. However, what I witness among scientists is the polar opposite: new hypotheses and theories are put to the test of multiple scientists around the world, and if, as happens sometimes, flaws are spotted in the science (or in the mathematics), scientists acknowledge that and move on either to search for alternative solutions or, perhaps as likely, to develop whole replacement hypotheses. Certainly, the team that proposes a hypothesis will vigorously defend it, as it intellectually healthily should; but just as certainly, the scientists that test it will do so with equal vigor and rigor, as they likewise should. Science typically doesn’t give ideas an easy ride; and ideologues, though rare, are unwelcome. Ideas get debunked all the time, rightly winnowing hypotheses so that only the proven percolate up and join the pantheon of the best. In the process, on mega scales, startlingly transformative phases occur, where whole new theories build on, sit side-by-side with, or replace established theories. (Newtonian physics, Einsteinian relativity, quantum mechanics being among them.) What I personally see is enthusiastic curiosity, inquisitiveness, and flexibility, rather than blinkered obduracy, within science.

A case in point, I believe, relates to the neutrinos — tiny, electrically neutral particles — discussed in the dialogue. As you probably recall, several years ago, a team of scientists working in a subterranean particle detector announced that they had detected neutrinos traveling faster (60 nanoseconds faster) than light — ostensibly violating Einstein’s theory of special relativity. However, separate teams of scientists, who had not been part of the original tests, performed critical examinations — according to science’s tradition — of the scientists' observation. They ended up disputing the findings by identifying an equipment fault that had resulted in a timing delay. Follow-on tests showed that the neutrino’s speed is indeed consistent with the speed of light — put another way, neutrinos obey light’s speed limit. (Conforming to the principle that particles with mass=0 travel at the speed of light.) In short, I propose that this discrete example of subjecting scientific ideas to the crucible of hard-nosed, objective tests — institutional rigor exemplified — is the rule, not the exception, in science.


Muneeb has always been a genius. He is a whirlwind of ideas. I wish he was born in 1900's, physics today would have been different.

Keith said...

The dialogue poses many interesting ideas, as I mention in my comment above. I’d like to explore a couple of them a little more — thinking out loud, shall we say, in an attempt to make a few basic connections.

Some of these ideas begin to be framed by the dialogue asking this question: “Thinking about the 'problem' of where the energy in the universe came from, isn't it perfectly logical to simply say that there is no 'before' to be dealt with or explained?” This question, and other topics the dialogue raises, gets into the realm of speculation (physical cosmology). Many of these topics are being investigated; some searches might bear fruit, and others might result in dead ends (perhaps ultimately proving unknowable). But sure, if, as some opine, time came into being at the instant of the big bang, it wouldn’t make sense, as you suggest, to refer to what came ‘before’ — there wouldn’t be a ‘before’.

Alternatively, in a cosmological model that posits an infinite, cyclical succession of big bangs, epochs of inflation, cosmic expansions, big crunches or (more likely) eternal expansion, time’s presence before our universe’s big bang would indeed make more sense. The same would be true if the multiverses that the dialogue speculates about were to follow a model of infinite bubble-like cosmoses forming and disappearing, both sequentially and simultaneously. Each such universe might have different laws of physics. But how to prove the universes’ existence, despite hypotheses offered to date, is, to engage in understatement, a thorny challenge.

Along these lines, the dialogue also mentions dark matter and dark energy, which relate to what happened at the universe’s start and how it all ‘settled down’ following the initial, brief ‘inflationary’ period. Again, there is speculation involved, though to be fair, scientists believe they have some understanding of these concepts. So, for example, evidence has shown that although the universe’s early expansion was slowing because of gravity yanking things toward each other, its later expansion (starting at roughly the 7-billion-year mark) was unexpectedly shown — including via the Hubble’s observation of supernovas — to be accelerating.

These observations relate to the universe’s makeup: about 70 percent being dark energy, 25 percent being dark matter, and the remaining modest portion, 5 percent, being all the matter (galaxies, stars, planets, and other stuff) we get to see. The connection is that physicists believe, as one explanation, that it’s the repulsive forces of dark energy that pull galaxies apart. Which loops back to the point about “the energy in the universe” that the dialogue raises in the question quoted above. As for the dialogue’s interesting speculation about the possible presence of “extra-bright matter” and “extra-bright energy,” discussion of the science — even if speculative — that inspires those notions would likely interest readers.

In context of the question above, there’s what the dialogue also touched on: cosmic inflation at the universe’s beginning. The inflationary period — an exponential expansion of space-time (like an inflating balloon) — is thought to have lasted from between 10-36 and 10-32 seconds after the singularity and big bang . . . in other words, a tiny fraction of a second. The natural laws were different then, though how different isn’t yet known. The ‘inflation’ hypothesis, however, is contentious. That said, per the dialogue’s getting into the upper limits of the speed of light — true for things moving through space — this inflationary expansion of space-time itself occurred faster than light. That is, the universe’s “edges” were expanding away from each other faster than light’s speed — possible given that no information (like a light pulse) was being transmitted, and hence the edges couldn’t “see” each other.

Your dialogue, Martin and Muneeb, is a good starting point for such conversations — or as you put it, “Over to you, or anyone reading.”

docmartincohen said...

Intriguing speculation! How might it be different? But I do find Muneeb's ideas a deep pool to fish in...

docmartincohen said...

This is the version of the onward march of rational science that Thomas Kuhn convincingly (I think anyway!) refuted.

On the specific case of the speed of light, the problem raised here is that it is defined rather than discoverable - isn't it? So the poor neutrinos are going to have to go at that speed, whether they like it or not...

docmartincohen said...

Thank you, Keith!

Keith said...

I’ll certainly defer to you, Martin, as to the correct understanding of Thomas Kuhn’s philosophy of science; you know it far better than I. But, at the risk of my wading into murky waters, let me offer a few related thoughts. I suppose, for example, that if it had been confirmed that the neutrinos did indeed travel faster than light, the result would have been a Kuhn-like ‘paradigm shift’ (revolution) within physics. With unimaginably far-reaching implications. So, the fact that Kuhn’s so-called ‘normal science’ was what disproved the experiment’s otherwise attention-grabbing results — and by extension, critically reaffirming light’s upper speed limit! — was itself nonetheless significant science, despite its being pigeonholed by the somewhat pejorative term ‘normal’ science. Alas, ‘normal’ sounds a mite like ‘uncreative’ and ‘non-innovative’ — and if so, a regrettable disservice, I would argue, to non-paradigmatic science, which contributes large strides to our understanding the natural world. To my mind, when Kuhn-like paradigm shifts, of which quantum theory must be a prime example, occur in science and result in radically different scientific fundamentals, with enough time those paradigm shifts (revolutions) too eventually turn to the backing of ‘normal science’ to widen the edges of theory. Kuhn’s normal science is what, not uncommonly, expands the fundamentals of paradigmatically new science both to concrete applications and, ambitiously, to our larger understanding of the underpinnings of reality. (My apologies, Martin, if I did a disservice to Kuhn here!)

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