Read this phrase from Hubblesite and was confused, “In 1929, Edwin Hubble provided the first observational evidence for the universe having a finite age. Using the largest telescope of the time, he discovered that the more distant a galaxy is from us, the faster it appears to be receding into space. This means that the universe is expanding uniformly in all directions.”
If the speed of expansion is uniform, shouldn’t distance not even be a variable?
In: 121
It’s not the speed of expansion that is uniform, but the rate.
Given any two points in space, the space between them is growing. But the amount it grows depends on how big it currently is.
The Hubble not-quite-a Constant is usually written as 90km/s/Mpc, but in SI units that works out to be about 2.27×10^(−18) /s.
This means that given any length, that length increases by a factor of 2.27×10^(−18) every second.
Two things that are 1m apart now, will be about 1 + 2.27×10^(−18)m apart a second later (in theory, this doesn’t happen in practice due to other forces).
But things that are 2m apart will be about 2 + 4.54×10^(−18)m apart a second later. The expansion is proportional to the current distance.
This means that things that are far apart get further apart faster than things that are closer together. The expansion happens at the same rate, but the relative speed is proportional to the distance.
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