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Spacetime vs speed of light varying with position

Posted 3 months ago
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In one of his videos in the Wolfram YouTube channel, S. Wolfram said:

If I wanted to pick a possible wrong term in the history of physics, which is probably about 100 years ago, it would be when people [Poincaré, Minkowski, etc.] started saying that space and time are the same kinds of things.

Indeed, in the English translation of his 1920 book "Relativity: the special and general theory" A. Einstein wrote:

according to the general theory of relativity, the law of the [speed] of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity [...] cannot claim any unlimited validity. A curvature of rays of light can only take place when the [speed] of propagation of light varies with position.

So, for A. Einstein, what other physicists called the curvature of spacetime, was the fact that the speed of light varies with position. For more details, I recommend the lecture Why Herrmann Minkowski Was a Disaster for Physics of Alexander Unzicker.

Posted 15 days ago

Spacetime is elegant and fun in some ways, but boy it sure does seem to be kinda wrong, huh? The idea of treating time as a spatial dimension makes for some interesting thought experiments (if you consider time a spatial dimension then you are part of a several billion year long branching tree stretching back in time all the way to the first common ancestor single cell and every creature to have lived in your chain of ancestry is touching like some kind of hyperspace hands across America).

But yeah, treating time as something akin to space in that way kind of ignores its pretty obvious expression as a consequence of causality kind of playing out, in the same way that Zeno shot an arrow at Euclid that he never recovered from (infinitely divisible space makes way less sense than space being a result of networked processing nodes of some sort, Wolfram has a pretty strong contender for describing that).

I spent years asking every physicist I met what distance was and why some things were further away from things than other things and they mostly just got annoyed, Wolfram is the first one to incidentally offer an answer to that question while also answering a whole lot of other questions, just by showing us how to better think about them.

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