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That blew my mind! So now it turns out Einstein was wrong?? We can't get particle to seriously travel faster than light and there is entire galaxy going faster

That blew my mind! So now it turns out Einstein was wrong?? We can't get particle to seriously travel faster than light and there is entire galaxy going faster??

dsmithatx 11y ago
I don't think it means Einstein was wrong or that one galaxy is moving "faster than the speed of light". It means in respect to each other two galaxies are moving faster than the speed of light. In other words each of two galaxies is going faster than half the speed of light, one of them being us (in relation to the other observed Galaxy).
- tamana 11y ago
  That's extremeley not true, and the whole point of Relatively is to explain why.
deleted 11y ago
[deleted]
joehilton 11y ago
I've also had a long-time question around this point. I've asked various university physics professors, and they all stutter and disagree (which means either we really don't know or I'm going to all the wrong universities). The underlying question is: When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? If it's photons emitting from flashlights pointed in opposite directions relative to each other, then are they compressing space as they travel so as not to exceed the speed of light? Or even massive particles accelerated to over half the speed of light at different times around an ellipse so there is a moment when their opposite directions make one traveling at greater than the speed of light relative to the other? (Or even particle accelerators on two different planets already expanding away from each other - does this just mean that space is really twisting and turning all the time to make sure no particle ever exceeds the speed of light relative to any other particle?) It has been my understanding - and appreciation at Einstein's unbelievable insight and brilliance - that relativity is truly relative because there really isn't any such thing as an arbitrary particle or space that all other motions are measured from. But if this is true, does that really mean that space is really so constantly twisting and turning that SOL can't be exceeded? I'm sure there are great answers to this, but I've always wanted a definitive one. Anyone have any comments on this?
- dsmithatx 11y ago
  "When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to?" It's a theory postulating that a particle can't travel faster than the speed of light in relationship to a particle that isn't moving. In practice all particles are moving in relation to some other particle thus it's not something you can visibly measure or see. At least that is the way I always viewed it.
- solipsism 11y ago
  does that really mean that space is really so constantly twisting and turning that SOL can't be exceeded? IANAP, but I've never read that space twists to prevent the SOL from being exceeded. I think you're thinking of time and mass. It would require an infinite amount of time or infinite acceleration to for something to accelerate to the speed of light relative to something else. Space is twisted by the presence of matter, and we call that gravity. If it's photons emitting from flashlights pointed in opposite directions relative to each other, then are they compressing space as they travel so as not to exceed the speed of light No. My understanding is that from the point of view of a photon time is completely stopped. Nothing moves relative to it because of this. Since nothing moves relative to it, nothing is exceeding the speed of light relative to it.
- VeilEm 11y ago
  > The underlying question is: When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? It's based on the observation of two points of references moving a different speeds shining light and the light from each traveling at the same speed. So the speed of light is measured relative to other light. The speed of light is constant, and it is so regardless of point of reference. Flashlights pointed in opposite directions has nothing to do with the speed of light. The light is traveling at the same speed in opposite directions.
- pdonis 11y ago
  > When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? Relative to a local inertial frame, i.e., relative to an inertial observer (i.e., an observer in free fall, feeling no force) who is at the same spatial location as the particle whose speed is being measured. That is the only context in which the concept of "relative velocity", as it appears in the "can't travel faster than light" condition, has any physical meaning. All of your suggested examples attempt to compare "relative velocity" between objects that are not at the same spatial location. That has no physical meaning in GR.
asgfoi 11y ago
The galaxy isn't traveling faster than c away from us, but space is being created in between. So, nothing is actually accelerating, there is no problem, Einstein is still right. In fact, space is being created everywhere, including yourself and the computer screen. However the amount is so small that you don't notice and local forces nullify the change anyway. With large distances, this amount accumulates, and overwhelms the force of gravity and starts to create the apparent acceleration of distant galaxies away from us. Further explanation from paulddraper: https://news.ycombinator.com/item?id=11068125 https://news.ycombinator.com/item?id=11068125
- joehilton 11y ago
  Yes, this makes sense. If this is the case though, then aren't there some obvious problems with how we think of dimensions (at least the first three or four anyway)? It seems like creating space to fill the "voids" between particles moving at-what-would-be-faster than the speed of light is like a tesseract for whatever matter is in that rapidly created/expanding space. Unless that space is only accessible to the particles creating it by their relative motion (which still gives us problems with our ideas of dimensions)?
- pdonis 11y ago
  This isn't really correct. Expansion of space is not the same thing as accelerated expansion of space. Aaccelerated expansion is indeed due to something "pushing" objects apart--that something is called "dark energy". But expansion itself, apart from the effects of dark energy, does not push on anything; it doesn't exert any force that moves objects apart or works against gravity. So thinking of ordinary expansion (apart from accelerated expansion) as "creating space" in between objects isn't really correct. It's unfortunate that so many pop science treatments use this way of speaking, since it leads to the incorrect inference I've just described.
  - asgfoi 11y ago
    The space is expanding and its expansion rate is accelerating. Dark energy is not pushing objects apart, it is causing the acceleration of expansion of space. What you said isn't even pop science, it is blatantly wrong. https://en.wikipedia.org/wiki/Metric_expansion_of_space https://en.wikipedia.org/wiki/Metric_expansion_of_space https://en.wikipedia.org/wiki/Dark_energy https://en.wikipedia.org/wiki/Dark_energy And the money quote: It is called "dark" because it is not interacting with normal matter, but only with the space time structure. from http://physics.stackexchange.com/a/206217 http://physics.stackexchange.com/a/206217
revscat 11y ago
The galaxies themselves are not moving faster than the speed of light, their relative distances are because of the rate of the expansion of the universe.
lutusp 11y ago
> That blew my mind! So now it turns out Einstein was wrong?? No, because the light speed limit only applies to things moving through space, not to space itself, which can and does expand faster than light speed. > We can't get particle to seriously travel faster than light and there is entire galaxy going faster?? The galaxy isn't traveling through space at faster than light speed, it's being conveyed along with the space that surrounds it at a speed that exceeds light-speed from the perspective of some distant location in space.

That blew my mind! So now it turns out Einstein was wrong?? We can't get particle to seriously travel faster than light and there is entire galaxy going faster??

dsmithatx 11y ago

I don't think it means Einstein was wrong or that one galaxy is moving "faster than the speed of light". It means in respect to each other two galaxies are moving faster than the speed of light. In other words each of two galaxies is going faster than half the speed of light, one of them being us (in relation to the other observed Galaxy).

tamana 11y ago
That's extremeley not true, and the whole point of Relatively is to explain why.

deleted 11y ago

[deleted]

joehilton 11y ago

I've also had a long-time question around this point. I've asked various university physics professors, and they all stutter and disagree (which means either we really don't know or I'm going to all the wrong universities). The underlying question is: When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? If it's photons emitting from flashlights pointed in opposite directions relative to each other, then are they compressing space as they travel so as not to exceed the speed of light? Or even massive particles accelerated to over half the speed of light at different times around an ellipse so there is a moment when their opposite directions make one traveling at greater than the speed of light relative to the other? (Or even particle accelerators on two different planets already expanding away from each other - does this just mean that space is really twisting and turning all the time to make sure no particle ever exceeds the speed of light relative to any other particle?) It has been my understanding - and appreciation at Einstein's unbelievable insight and brilliance - that relativity is truly relative because there really isn't any such thing as an arbitrary particle or space that all other motions are measured from. But if this is true, does that really mean that space is really so constantly twisting and turning that SOL can't be exceeded? I'm sure there are great answers to this, but I've always wanted a definitive one. Anyone have any comments on this?

dsmithatx 11y ago
"When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to?" It's a theory postulating that a particle can't travel faster than the speed of light in relationship to a particle that isn't moving. In practice all particles are moving in relation to some other particle thus it's not something you can visibly measure or see. At least that is the way I always viewed it.
solipsism 11y ago
does that really mean that space is really so constantly twisting and turning that SOL can't be exceeded? IANAP, but I've never read that space twists to prevent the SOL from being exceeded. I think you're thinking of time and mass. It would require an infinite amount of time or infinite acceleration to for something to accelerate to the speed of light relative to something else. Space is twisted by the presence of matter, and we call that gravity. If it's photons emitting from flashlights pointed in opposite directions relative to each other, then are they compressing space as they travel so as not to exceed the speed of light No. My understanding is that from the point of view of a photon time is completely stopped. Nothing moves relative to it because of this. Since nothing moves relative to it, nothing is exceeding the speed of light relative to it.
VeilEm 11y ago
> The underlying question is: When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? It's based on the observation of two points of references moving a different speeds shining light and the light from each traveling at the same speed. So the speed of light is measured relative to other light. The speed of light is constant, and it is so regardless of point of reference. Flashlights pointed in opposite directions has nothing to do with the speed of light. The light is traveling at the same speed in opposite directions.
pdonis 11y ago
> When we say in general relativity that particles can't travel faster than light, what is that speed measured relative to? Relative to a local inertial frame, i.e., relative to an inertial observer (i.e., an observer in free fall, feeling no force) who is at the same spatial location as the particle whose speed is being measured. That is the only context in which the concept of "relative velocity", as it appears in the "can't travel faster than light" condition, has any physical meaning. All of your suggested examples attempt to compare "relative velocity" between objects that are not at the same spatial location. That has no physical meaning in GR.

asgfoi 11y ago

The galaxy isn't traveling faster than c away from us, but space is being created in between. So, nothing is actually accelerating, there is no problem, Einstein is still right. In fact, space is being created everywhere, including yourself and the computer screen. However the amount is so small that you don't notice and local forces nullify the change anyway. With large distances, this amount accumulates, and overwhelms the force of gravity and starts to create the apparent acceleration of distant galaxies away from us. Further explanation from paulddraper: https://news.ycombinator.com/item?id=11068125 https://news.ycombinator.com/item?id=11068125

joehilton 11y ago
Yes, this makes sense. If this is the case though, then aren't there some obvious problems with how we think of dimensions (at least the first three or four anyway)? It seems like creating space to fill the "voids" between particles moving at-what-would-be-faster than the speed of light is like a tesseract for whatever matter is in that rapidly created/expanding space. Unless that space is only accessible to the particles creating it by their relative motion (which still gives us problems with our ideas of dimensions)?
pdonis 11y ago
This isn't really correct. Expansion of space is not the same thing as accelerated expansion of space. Aaccelerated expansion is indeed due to something "pushing" objects apart--that something is called "dark energy". But expansion itself, apart from the effects of dark energy, does not push on anything; it doesn't exert any force that moves objects apart or works against gravity. So thinking of ordinary expansion (apart from accelerated expansion) as "creating space" in between objects isn't really correct. It's unfortunate that so many pop science treatments use this way of speaking, since it leads to the incorrect inference I've just described.
- asgfoi 11y ago
  The space is expanding and its expansion rate is accelerating. Dark energy is not pushing objects apart, it is causing the acceleration of expansion of space. What you said isn't even pop science, it is blatantly wrong. https://en.wikipedia.org/wiki/Metric_expansion_of_space https://en.wikipedia.org/wiki/Metric_expansion_of_space https://en.wikipedia.org/wiki/Dark_energy https://en.wikipedia.org/wiki/Dark_energy And the money quote: It is called "dark" because it is not interacting with normal matter, but only with the space time structure. from http://physics.stackexchange.com/a/206217 http://physics.stackexchange.com/a/206217

revscat 11y ago

The galaxies themselves are not moving faster than the speed of light, their relative distances are because of the rate of the expansion of the universe.

lutusp 11y ago

> That blew my mind! So now it turns out Einstein was wrong?? No, because the light speed limit only applies to things moving through space, not to space itself, which can and does expand faster than light speed. > We can't get particle to seriously travel faster than light and there is entire galaxy going faster?? The galaxy isn't traveling through space at faster than light speed, it's being conveyed along with the space that surrounds it at a speed that exceeds light-speed from the perspective of some distant location in space.