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Mass and angular momentum, left ambiguous by Einstein, get defined

quantamagazine.org

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Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#41

Post by pdonis »

adelarsq wrote: post #39
pdonis wrote: post #36

Earlier quoted context omitted.

> 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.

At same time that a center does not exists it exists. Take a line between the two sides from the theoretical border, divide in the middle and will be a center. But isn't a center.

> 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.

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#42

Post by leephillips »

hinkley wrote: post #7

Maybe a year ago, possibly here, I finally saw gyroscopic precession demonstrated in a way that didn’t invoke magic thinking. The person simply pointed out that the mistake is in thinking of the rotating mass as a stationary object, when in fact you are applying the lateral force to a different spot on the object at each time interval, leading to very strange vectors.

Does this have something to do with the article?

I don’t recall any “magic thinking” in the explanation of precession in my introductory undergraduate physics text. Just Newton’s laws and vector cross-products.

“you are applying the lateral force to a different spot on the object at each time interval” : how is that applied when the force is gravity, applied to every point of the object at every time?

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#43

Post by snarfy »

323 wrote: post #40
shadowgovt wrote: post #2

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…

Why is it a requirement for the experiment information to get back to the originating point right away? We do all the time experiments where the information is re-converged much later, even months later like at the LHC. We tested many times the speed of light on earth, and we know that so far no directional speed difference was detected over earthly distances, which you say it's an impossible statement to make.

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

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#44

Post by leephillips »

aliraheem wrote: post #31
polishdude20 wrote: post #24

Earlier quoted context omitted.

Is there a link to a resource on this or was it just in person? I'd love to hear the intuition you describe!

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.

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#45

Post by x3n0ph3n3 »

qsdf38100 wrote: post #4
shadowgovt wrote: post #2

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.

That video was pretty bad, though. It completely ignores everything we know about the CMB. If it were true that the speed of light was different in different directions, the CMB would look very different.

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#46

Post by x3n0ph3n3 »

snarfy wrote: post #43
323 wrote: post #40

Earlier quoted context omitted.

Why is it a requirement for the experiment information to get back to the originating point right away? We do all the time experiments where the information is re-converged much later, even months later like at the LHC. We tested many times the speed of light on earth, and we know that so far no directional speed difference was detected over earthly distances, which you say it's an impossible statement to make.

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.

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#47

Post by xavxav »

sytelus wrote: post #33
shadowgovt wrote: post #2

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…

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…

The visualization that works for me is to imagine the surface of a balloon as a 2D universe. As you inflate the balloon it stretches out despite the skin having no “center” to speak of.

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#48

Post by lovich »

kolinko wrote: post #13
tasty_freeze wrote: post #10

Earlier quoted context omitted.

I get what you are saying, it suggests there is no preferred direction, but it is just an inference. The point is one cannot create an experiment to measure the speed of light other than a round trip average speed.

Red shift would be different in various directions then. We would also see fewer young galaxies / stars in the direction in which light flies faster.

That would imply an axiom that forces/light/whatever are on a gradient we operate against and does not change based on reference point.

I think the heart of the what the GP is getting at is no matter how you define it, you can measure things smaller than your measuring equipment can detect.

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#49

Post by lamontcg »

shadowgovt wrote: post #2

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…

I know that classical rotational symmetry leads to conservation of angular momentum by Noether's theorem.

I suspect if you break the rotational symmetry of the speed of light that you wind up breaking something like conservation of quantum spin angular momentum and the universe rapidly becomes nonsensical.

Re: Mass and angular momentum, left ambiguous by Einstein, get defined

#50

Post by renox »

sytelus wrote: post #33
shadowgovt wrote: post #2

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…

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…

The classical 'visualisation' of this is 'cake expansion'.

If you think about what's happening inside a cake when you put it in an oven, it expands in all directions, and the center has only a meaning there because the cake is finite.

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