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T.O.E Dream
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If the speed of light takes sometime to travel a certain distance and that distance expands (like for example the universe expanding) then wouldn't time have to speed up to keep the speed of light constant?
T.O.E Dream said:So take two points, maybe of a distance of one light second. Now if the space expanded the two points are further away and not a light second apart. But don't we already know that the speed if light is the only constant?
If i were to measure a meter in space and then the space expands by 2 times would it still be a meter or does it change to 2 meters?
Each solution of Einstein's equation describes a possible geometry of spacetime. One important class of solutions was discovered in the 1920's. They are called FLRW solutions (at least by Wikipedia). To find them, you start with the assumption that spacetime can be sliced into a one-parameter family (with time being the parameter) of 3-dimensional spaces St ("spacelike hypersurfaces") that you can think of as "space, at time t". You also assume that each of these hypersurfaces is homogeneous (translationally invariant) and isotropic (rotationally invariant). (You would have to use a very technical definition of the concepts "homogeneous" and "isotropic").stone1 said:I have a similar question (if not the same question really). If there is no space and there is no time, but only spacetime, why do people talk about space expanding? Is spacetime expanding?
I have never really been able to make sense of that explanation. Gravity isn't even a force in GR, so how does it make sense to say that the reason is that gravity is weaker? How do you even compare them?Naty1 said:Empty space itself is rather weakly held together; masses like meter sticks are held by relatively strong forces like electromagnetic attraction and nuclear forces. Even gravity, usually considered the weakest of the forces at everyday distances is often stronger than the cosmological expansion: our galaxy is pretty much held together by gravity but at intergalactic distances where there is a lot more empty space, space is apparently able to expand.
Not really. It just has a time dependent scale factor.T.O.E Dream said:If space is expanding than it is obvously moving.
I don't understand this question.T.O.E Dream said:Wouldn't that mean we need to apply relativity for space?
Fredrik said:Now all of these solutions have the property that the time parameter t can only be defined for values of t larger than some value which we can choose to be 0, and all of them have the property that as t grows, so does St (in one of the three main classes of solutions St reaches a maximum size after a while and then starts shrinking). The geometry of any St can be described by a formula that's the same for all t, except for a number R(t) called a scale factor. In all of these solutions we have R(t)→0 as t→0.
The concept of time speeding up as the universe expands is a bit of a misconception. Time does not physically speed up, but rather the rate at which time is experienced may change due to changes in the universe's expansion. This phenomenon is known as time dilation.
The expansion of space can affect the rate of time due to the theory of general relativity. As space expands, it can cause a curvature in spacetime, which can lead to time dilation. This means that time may appear to pass slower for objects in regions of strong gravitational pull, such as near massive galaxies.
Time dilation and time speeding up are not the same thing. Time dilation refers to a difference in the rate at which time is experienced due to factors such as gravity or velocity. Time speeding up, on the other hand, implies that time is actually moving faster, which is not the case.
Yes, we can observe the effects of time dilation in everyday life. For example, GPS satellites have to account for time dilation due to their high speeds in orbit, or else their location calculations would be off by several meters. Additionally, astronauts in space experience time dilation due to their proximity to massive objects, such as the Earth.
It is predicted that time will continue to appear to speed up as the universe expands. This is because the expansion of space is accelerating, which will lead to more time dilation effects. However, the rate at which time appears to speed up may vary depending on the future state of the universe.