Monday, July 22, 2024

How Michelson-Morley was Crucial for Relativity

Alejandro Cassini, Leonardo Levinas write a new paper:
How the Michelson and Morley experiment was reinterpreted by special relativity
They note how relativity textbooks describe M-M as being crucial for relativity, and discuss whether this is historically accurate. It includes some interesting history, but omits the most important pieces to the puzzle.

Einstein's 1905 paper does not mention M-M. Later on he admitted that M-M was crucial for special relativity, but denied that he paid any attention to it.

FitzGerald, Lorentz, Poincare, and Minkowski all described relativity as a consequence of M-M. This paper does not even mention Poincare or Minkowski. It discusses Einstein a lot.

A paper on the influence of M-M on relativity should primarily be on those who were influenced, not Einstein.

In the years immediately following the M-M experiment, there was no inclination to conclude that the ether was non-existent, nor that the speed of light was constant even though the light source was in motion relative to the ether. Moreover, no one thought that the principle of relativity - the equivalence of all inertial frames of reference for the description of electromagnetic phenomena- would be confirmed. Nor did anyone think the hypothesis that the speed of light was invariant, that is, the same in any inertial frame of reference, would be confirmed.1 What exactly did this experiment confirm or refute?
Not true. In those years, Lorentz and Poincare did say that the speed of light was constant, and Einstein got that postulate from Lorentz. Poincare did say that the principle of relativity was confirmed, and Einstein got that terminology from him.

Lorentz did think that M-M refuted the aether motion theories.

M-M does not actually refute the aether. Belief in the aether is consistent with relativity. Einstein said so himself. M-M just refuted the idea that the Earth had a measurable motion against the aether.

As is well known, FitzGerald in 1889 and independently Lorentz in 1892 proposed a different interpretation. They argued that the experiment refuted the hypothesis that the length of the arms of the instrument remained unchanged when it was in motion relative to the ether, a tacit assumption of the M-M experiment. They then formulated the hypothesis that the length of rigid bodies that move with respect to the ether is not invariant, but rather contracts in the direction of motion
That's right. They saw the M-M as finding that measuring the speed of light did not depend on the frame of reference, and used that to deduce the Lorentz transformation.

It was similar to what Einstein did in 1905, except that Einstein did not use the M-M, but rather what Lorentz had deduced from Maxwell's equations and M-M -- that the speed of light is constant and appears the same in different frames.

At the time Einstein formulated it, it was the only explanation of the M-M experiment that was compatible with all known phenomena about the propagation of light, such as stellar aberration, Fizeau's experiment, and many others.28
No, that was all done by Lorentz in 1895. Lorentz even got a related Nobel Prize in 1902. Einstein did not attempt to explain M-M at all. You might say that Einstein was trying to give a recapitulation of Lorentz's 1895 theory, without mentioning M-M or other experiments.
The contraction hypothesis is usually considered to be purely ad hoc since it was proposed solely to accommodate the result of the M-M experiment in order to save the quiescent ether hypothesis from refutation. This affirmation is debatable and depends on what is understood by the concept of an ad hoc hypothesis.13
Here, "ad hoc" means deduced from M-M or other experiment. A theory is not ad hoc if it abstracts out principles from the experiment. There are some anti-positivist philosophers who consider ad hoc to be a bad thing.

The M-M really was crucial for relativity. Those who discovered the Lorentz transformations and spacetime all said so.

Monday, July 8, 2024

Posulating the Constant Speed of Light

D V Redžić writes in a new paper:
The historical path to special relativity starts from the second postulate introduced by Einstein in 1905 [10]. Immediately after the publication of reference [10],
No, the historical path starts with Maxwell's 1865 theory, and the motion invariance tests of it by Michelson in the 1880s.

A popular interpretation of the 1887 Michelson-Morley experiment was that the speed of light was the same for all observers.

Newton, and all physicists before Einstein (including Voigt, Larmor, Lorentz and Poincar´e [15-18]), took it for granted that there was only one ‘time,’ absolute Newtonian time, for all observers in motion with respect to one another. Einstein was bold enough to venture that each inertial observer has her/his own absolute Einsteinian time.
No. Moving objects had they own "local time" in Lorentz's 1895 relativity theory. Poincare accepted this, and believed that motion affects time. Not sure about Voigt and Larmor, but they gave equantions for time changing; what else could they have thought?

It is amazing that someone could write a commentary on on the historical path of relativity, and act as if it all started and ended with Eeinstein's 1905 paper.

Thursday, July 4, 2024

Google Quantum Supremacy is Smashed

NewScientist reports:
Google's claim of quantum supremacy has been completely smashed

Google's Sycamore quantum computer was the first to demonstrate quantum supremacy – solving calculations that would be unfeasible on a classical computer – but now ordinary machines have pulled ahead again

In 2019, Google claimed that its Sycamore quantum computer could perform calculations that would take even the world’s most powerful classical supercomputer 10,000 years to complete – but now it seems that a non-quantum computer crunches the numbers several times faster than Google’s machine, and uses less energy doing so.

Quantum computers have the potential to carry out some kinds of calculations vastly more quickly than classical computers, but are still in their infancy. Google announced in 2019 that Sycamore had achieved “quantum supremacy” – the point at which a quantum computer can…

The rest is paywalled, and I haven't read it, but I don't think I need to. Others have said the Google claim was refuted.

I was skeptical in 2019 for the simple reason that Google did not do something that known to be computationally difficult.. It merely generated some random numbers and then claimed that it would be hard for a classical computer to simulate it.

Then some Chinese researchers showed that it was not so hard to simulate it. Meanwhile the Google team moved on to other problems, rather than defend the integrity of their biggest accomplishment.

Without quantum supremacy, the whole field of quantum computing is a sham. No good can come of it.

Monday, July 1, 2024

David Z. Albert Plugs Bohmian Mechanics

New podcast, with a physicist interviewing a philosopher of physics:
Could physics serve as our best guide to metaphysics? What fundamental metaphysics is best motivated by quantum mechanics? And what’s the deal with the age-old feud between philosophers and physicists?

Here to shed light on all these questions and more is none other than David Z. Albert, professor of philosophy and director of the MA program in The Philosophical Foundations of Physics at Columbia University in New York. David is a prominent American philosopher and physicist widely recognized for his contributions to the philosophy of quantum mechanics and the foundations of physics. He has published four popular books and numerous articles on quantum mechanics.

I have some disagreements, but I was especially struck by this comment at the end:
1:19:40 last question, this one comes from my friend Professor Luke Barnes at Western Sydney. Luke. Yeah, he's a great friend of the show. 1:19:47 He's been on multiple times. he has he makes a controversial claim, as if bohmian mechanics have been proposed. First. 1:19:54 No one would have proposed the Copenhagen interpretation. Right. Your thoughts, sir? I think that's absolutely right. 1:19:59 I think, you know, somebody, somebody had discovered about me in mechanics. 1:20:06 And you imagine before then walking into a room and saying, no, I've got a whole new view. 1:20:12 Okay. it's much more elegant. It respects the symmetry between position 1:20:18 space and momentum space, blah, blah, blah. The only little catch is that you have to give up on the idea 1:20:25 that there's a real external world out there. Okay, I think you would have been laughed out of the room, right?
No, this is bizarre. Albert has written a lot about the philosophy of quantum mechanics, but this comment is so foolish that we should disregard everyone he says on the subject.

Bohmian mechanics is weirdly deterministic and nonlocal. While it has its own cult following, it is nearly useless for practical physics. It was invented to make a theoretical point about hidden variables, but not because it is a satisfactor interpretation.

Earlier, Albert said that quantum logics were too confusing, because he doesn't how to reason about it if regular logic is abandoned. I feel similarly about locality. Give it up, and I am not sure what you mean by experiments anymore, because you cannot isolate any physical processes.