4 ms·

So the galaxies are sitting still, the space inside it is expanding ... at faster than the speed of light. The way my puny layman mind can figure out ... if 2

So the galaxies are sitting still, the space inside it is expanding ... at faster than the speed of light. The way my puny layman mind can figure out ... if 2 objects move away from one another at slightly more than half the speed of light, then one would see the other as apparently moving away at greater than the speed of light. Also, iirc, the expanding balloon metaphor was more to give an idea how all points are moving away from one another, and each sees itself as the center. It was not meant to talk of dimensions, or moving into ... (btw, thanks a lot for the link. great read)

tydok 16y ago
> 2 objects move away from one another at slightly more than half the speed of light, ... IIRC, mass grows towards infinity as it approaches the speed of light. So that's not possible if the objects have mass.
- ErrantX 16y ago
  Which bit are you questioning - making it to half the speed of light (I believe that is entirely possible) or the relative speed being more than the speed of light? If it is the latter; it's perfectly possible. Ultimately it is just mathematics - as pointed out on Wikipedia apparent "FTL" travel is allowed by most models. http://en.wikipedia.org/wiki/Faster-than-light http://en.wikipedia.org/wiki/Faster-than-light
  - tydok 16y ago
    The first part, making it to half the speed of light. With massless particles is of course possible. My physics is a bit rusty so I can't really argue on this matter :)
- JoeAltmaier 16y ago
  Unless you change the "size" of the space between them - then they are getting further apart without moving, which is what is happening.
- crazydiamond 16y ago
  So are you saying there is a maximum speed which is less than half the speed of light, for objects that have mass. What is that max speed ?? From what i know, a great deal of energy is required to accelerate it, as the speed increases, but its still a finite amount.
  - retube 16y ago
    maximum speed for any object with mass is the speed of light in vacuo. You can't accelerate beyond this as, as you impart more energy to the object, it increases in mass, making it harder to accelerate further. As you approach c the mass tends -> infinite, hence requiring infinite energy to get to c. Objects with no mass on the other hand, all move at c.
lmkg 16y ago
Warning: special relativity hurts your brain. First, there's no such thing as objective space. There is no objective Frame of Reference. You can pick a frame of reference, and it should probably be an inertial (non-accelerating) frame of reference, but it's just as valid as any other frame of reference. Inertial frames of references move with respect to each other at constant, less-than-C velocity. Ok, so you picked a frame of reference, and in that frame of reference you have two objects A and B moving away from each other, each with a velocity of 0.5c, for a total relative velocity of c. What does this look like to either of the objects? Well, to answer that question, we have to jump into their frames of reference, which are moving at 0.5c with respect to ours. In this new frame of reference, one of the objects A is stationary. Object C that was stationary in the previous frame of reference is now moving at 0.5c. And the other object B, that in the previous frame of reference was moving away at c? In this frame of reference, it is moving away at less than c. Why? A combination of time dilation and space compression, which you probably know happens in special relativity. In the original frame of reference, object A was moving at 0.5c because it took 1 year to travel from one point to another than are half a light year apart. In the new frame of reference, the object A is standing still and the two points are moving, and they're more than half a light-year apart, and it takes less than 1 year for the new one to get here. Similarly, time & distance separation between points that the other object B is passing have altered in the new frame of reference. There's some math which isn't that complicated but is a bit onerous, but the punchline is that it appears to be traveling less than the speed of light in the new frame of reference. Why does space and time contort like this? So that a light particle traveling will appear to be moving at the speed of light in any inertial reference frame, regardless of the relative velocities of those reference frames.

tydok 16y ago

> 2 objects move away from one another at slightly more than half the speed of light, ... IIRC, mass grows towards infinity as it approaches the speed of light. So that's not possible if the objects have mass.

ErrantX 16y ago
Which bit are you questioning - making it to half the speed of light (I believe that is entirely possible) or the relative speed being more than the speed of light? If it is the latter; it's perfectly possible. Ultimately it is just mathematics - as pointed out on Wikipedia apparent "FTL" travel is allowed by most models. http://en.wikipedia.org/wiki/Faster-than-light http://en.wikipedia.org/wiki/Faster-than-light
- tydok 16y ago
  The first part, making it to half the speed of light. With massless particles is of course possible. My physics is a bit rusty so I can't really argue on this matter :)
JoeAltmaier 16y ago
Unless you change the "size" of the space between them - then they are getting further apart without moving, which is what is happening.
crazydiamond 16y ago
So are you saying there is a maximum speed which is less than half the speed of light, for objects that have mass. What is that max speed ?? From what i know, a great deal of energy is required to accelerate it, as the speed increases, but its still a finite amount.
- retube 16y ago
  maximum speed for any object with mass is the speed of light in vacuo. You can't accelerate beyond this as, as you impart more energy to the object, it increases in mass, making it harder to accelerate further. As you approach c the mass tends -> infinite, hence requiring infinite energy to get to c. Objects with no mass on the other hand, all move at c.

lmkg 16y ago

Warning: special relativity hurts your brain. First, there's no such thing as objective space. There is no objective Frame of Reference. You can pick a frame of reference, and it should probably be an inertial (non-accelerating) frame of reference, but it's just as valid as any other frame of reference. Inertial frames of references move with respect to each other at constant, less-than-C velocity. Ok, so you picked a frame of reference, and in that frame of reference you have two objects A and B moving away from each other, each with a velocity of 0.5c, for a total relative velocity of c. What does this look like to either of the objects? Well, to answer that question, we have to jump into their frames of reference, which are moving at 0.5c with respect to ours. In this new frame of reference, one of the objects A is stationary. Object C that was stationary in the previous frame of reference is now moving at 0.5c. And the other object B, that in the previous frame of reference was moving away at c? In this frame of reference, it is moving away at less than c. Why? A combination of time dilation and space compression, which you probably know happens in special relativity. In the original frame of reference, object A was moving at 0.5c because it took 1 year to travel from one point to another than are half a light year apart. In the new frame of reference, the object A is standing still and the two points are moving, and they're more than half a light-year apart, and it takes less than 1 year for the new one to get here. Similarly, time & distance separation between points that the other object B is passing have altered in the new frame of reference. There's some math which isn't that complicated but is a bit onerous, but the punchline is that it appears to be traveling less than the speed of light in the new frame of reference. Why does space and time contort like this? So that a light particle traveling will appear to be moving at the speed of light in any inertial reference frame, regardless of the relative velocities of those reference frames.