71–80 of 125 posts
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Here it is https://science.howstuffworks.com/gyroscope.htm#pt2 I've never thought much of it.
The misleading and faulty explanation in this link talks about the “desire” of a point on the wheel to move in a certain direction. Now that’s some magical thinking.
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> Take a line between the two sides from the theoretical border There is no "border" to our universe. The fact that you have trouble visualizing such models does not mean they don't exist.
There is an "effective" border because of speed of light limits. Technically we are "at the center" of our intractable universe.
We are at the center of our observable universe, yes, but that fact does not support any of the claims I have been responding to in this thread.
The most eye-opening thing I've learned about relativity in the past few years is that the notion that space has no preferential direction is an axiom in the theory. There's nothing about the way we measure the speed of light that would disambiguate if light traveled instantaneously in one direction and at half the measured speed of light in the other. We just don't have a way to know, because time measurements requi…
This was the case in special relativity, with a flat space-time. In general relativity, space-time is curved and there are locally special directions. The laws of Physics still do not define special directions a priori. It is quite fundamental actually, and so far everything behaves as expected, at least in this respect. It is not as much an axiom as a consequence of Maxwell’s equations, from which we can deduce that light has a well-defined velocity in vacuum, irrespective of location or direction.
> There's nothing about the way we measure the speed of light that would disambiguate if light traveled instantaneously in one direction and at half the measured speed of light in the other.
There is something I don’t get here. If we shine a light on a detector, we can measure the time the light takes to reach the detector. Are you saying that the light hits the detector instantly, and then goes back to the source, or that the detector is the source and the light comes back to it after hitting the source instantly?
In practice, the speed of light does not depend on direction, as far as we can measure.
From a layman's perspevtive I've never understood the existence of angular momentum as anything other than a mental model or abstraction. My intuition tells me that all momentum is only linear (except maybe at the fundamental particle level), and perceived rotation is really just a huge amount of linear interactions by individual particles that make up a larger object. This is similar to how a gas is not really a sin…
It's very decidedly not an abstraction on linear momentum. It's a conserved quantity just like any other. Light has angular momentum even when travelling in a straight line. Anything with spin does even when stopped. In physics there is a concept known as symmetry. Any way you can swap around your variables without influencing the answers corresponds to a way in which the laws of physics are symmetric (or a way someo…
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Wasn't that the whole idea behind Michelson-Morley ( https://en.wikipedia.org/wiki/Michelson%E2%80%93Morley_exper... )?
Yes, that is an example of a measurement of the two-way speed of light. What is impossible, however, is a measurement of the one-way speed of light.
The most eye-opening thing I've learned about relativity in the past few years is that the notion that space has no preferential direction is an axiom in the theory. There's nothing about the way we measure the speed of light that would disambiguate if light traveled instantaneously in one direction and at half the measured speed of light in the other. We just don't have a way to know, because time measurements requi…
Veritasium has a nice video about it on YouTube. We can only measure the average back and forth speed of light.
He is often wrong in subtle and not—subtle ways, though. In this case, regardless of the issue of one-way measurements of c, his sources do not really support an anisotropy in the speed of light.
His video was mentioned already 5 or 6 times here. Isn’t here anything better at all?
The most eye-opening thing I've learned about relativity in the past few years is that the notion that space has no preferential direction is an axiom in the theory. There's nothing about the way we measure the speed of light that would disambiguate if light traveled instantaneously in one direction and at half the measured speed of light in the other. We just don't have a way to know, because time measurements requi…
> the notion that space has no preferential direction is an axiom in the theory. This was the case in special relativity, with a flat space-time. In general relativity, space-time is curved and there are locally special directions. The laws of Physics still do not define special directions a priori. It is quite fundamental actually, and so far everything behaves as expected, at least in this respect. It is not as muc…
It could well be the same magnitude each direction or it could be instantaneous one way and 1/2 c back the other or any other combination of values as long as the average of the two way measurement is c.
Final note: the value that we put as c is only true in a very specific environment. It depends on the characteristics of the medium through which light is traveling as to what we will measure as the average two way speed. This is a consequence of the permeability and the permittivity of the medium through which the light is traveling. This is standard electrical engineering fare.
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We've never actually measured the speed of light in one direction. It's impossible. Vertasium video on the subject - https://www.youtube.com/watch?v=pTn6Ewhb27k
If it were true that the speed of light is different in different directions, the CMB would look completely different than it does. This was a major oversight in Veritasium's video.
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It's a great axiom until it isn't. One thing I still cannot visualize is exapanding universe. If there is an expanstion then there must be a shape and then there must be a center and then must be one direction that is not exactly same as another because expansion rates are different. I read that universe expands same everywhere and there is no "center" which is very hard to visualize but it is a requirement for this…
> If there is an expanstion then there must be a shape and then there must be a center However intuitively plausible this seems to you, it's still false. The fact that our intuitive visualization capabilities cannot directly visualize the mathematical entities involved does not change that.
If those axioms are changed, you get a different logical and mathematical outcome.