OK, I am highly impressed by the amplituhedron as an innovative way of lumping Feynman diagrams together and deriving their sum – thank you for the references – but its originators have no time for variable-c, and I don’t either. Nor do I think much of the twistor program as a way to derive spacetime corresponding to the intersection of null lines; twistor algebra is merely a mutilated part of a Clifford algebra, as was shown in “Geometric Algebra for Physicists” by Chris Doran and Anthony Lasenby. If you use the full Clifford Algebra then you can do a lot better. So although I am sympathetic to attempts to derive spacetime for the reasons explained, I don’t think this is the way to do it. The amplituhedron is certainly a step forward toward *something*, though.

]]>Phillip: We might be no nearer finding a unified Lagrangian but, even though a Lagrangian for GR has long been known, the fact that it can be recast as a gauge theory despecialises it, which is a huge conceptual leap forward.

]]>‘Interpretation’ enters only when something isn’t clear.

]]>“But what is your evidence that lightspeed is not constant”

Any relevant experiment – Michelson-Morley, Pound-Rebka, Doppler measurements – if interpreted correctly, confirms Newton’s variable speed of light. Example:

Stationary emitter; moving receiver: http://www.einstein-online.info/images/spotlights/doppler/doppler_detector_blue.gif

(Website: http://www.einstein-online.info/spotlights/doppler.html)

The speed of the light pulses relative to the emitter is

c = df

where d is the distance between the pulses and f is the frequency measured by the emitter. The speed of the pulses relative to the receiver is

c’= df’ > c

where f’ > f is the frequency measured by the receiver.

]]>This looks interesting, because the irrelevance of space and time to the correlations inferred in Bell tests – as correctly predicted by quantum mechanics – is strong evidence that spacetime is not fundamental at the next ontological level (which I call the level of the hidden variables, because it enables deterministic prediction of measurements predicted by QM only probabilistically). But what is your evidence that lightspeed is not constant at our present level of description? Our present theories have been tested to very high accuracy and rest on that assumption.

I also disagree that you need the next ontological level in order to unify gravity with the other forces. Gravity can perfectly well be phrased as a gauge theory, just like the others. Then all you need is a unified Lagrangian. The real reason a deeper ontological level is required is to dispel neo-Copenhagenite nonsense that there is no reason why two identical systems behave differently under quantum measurement. String theory is ultimately still quantum so it cannot, even in principle, be the last word.

]]>The speed of light either depends on the speed of the emitter (Newton’s theory) or is independent (ether theory and Einstein’s relativity). Where is the truth? The answer was given, implicitly, in 1887. Dependence proved directly. Independence, “without recourse to contracting lengths, local time, or Lorentz transformations”, disproved:

Banesh Hoffmann, Relativity and Its Roots, p.92: “Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton’s laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether.” https://www.amazon.com/Relativity-Its-Roots-Banesh-Hoffmann/dp/0486406768

Wikipedia: “Emission theory, also called emitter theory or ballistic theory of light, was a competing theory for the special theory of relativity, explaining the results of the Michelson–Morley experiment of 1887. […] The name most often associated with emission theory is Isaac Newton. In his corpuscular theory Newton visualized light “corpuscles” being thrown off from hot bodies at a nominal speed of c with respect to the emitting object, and obeying the usual laws of Newtonian mechanics, and we then expect light to be moving towards us with a speed that is offset by the speed of the distant emitter (c ± v).” https://en.wikipedia.org/wiki/Emission_theory

]]>Nima Arkani-Hamed (06:09): “Almost all of us believe that space-time doesn’t really exist, space-time is doomed and has to be replaced…” https://youtu.be/U47kyV4TMnE?t=369

“We’ve known for decades that space-time is doomed,” says Arkani-Hamed. “We know it is not there in the next version of physics.” http://discovermagazine.com/2014/jan-feb/10-shaping-the-future-of-physics

Nobel Laureate David Gross observed, “Everyone in string theory is convinced…that spacetime is doomed. But we don’t know what it’s replaced by.” https://www.edge.org/response-detail/26563

What scientific idea is ready for retirement? Steve Giddings: “Spacetime. Physics has always been regarded as playing out on an underlying stage of space and time. Special relativity joined these into spacetime… […] The apparent need to retire classical spacetime as a fundamental concept is profound…” https://www.edge.org/response-detail/25477

“Rethinking Einstein: The end of space-time. […] Horava, who is at the University of California, Berkeley, wants to rip this fabric apart and set time and space free from one another in order to come up with a unified theory that reconciles the disparate worlds of quantum mechanics and gravity – one the most pressing challenges to modern physics.” https://www.newscientist.com/article/mg20727721-200-rethinking-einstein-the-end-of-space-time/

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