The Hubble Law states that space expands evenly everywhere, even though all galaxies in space are more or less not moving at all!But because Einstein’s Special Theory of Relativity makes no statement about how space canexpand, but only how things can move in space, an overlight-fast relative velocity caused by space expansion is not in the Contradiction to the statement “Nothing flies faster in space than the light!”.
And now think again:
- We sketch four dots on a piece of paper.
One point represents our Earth, the other three each represents a galaxy. The distances in between are always exactly one light-year high.
As a result, galaxy A is away from Earth at 100 km/s. Galaxy B also distances itself from galaxy A at 100 km/s. And galaxy C is of course also away from galaxy B at 100 km/s.
Galaxy B not at 50 km/s, but at 100 km/s + 100 km/s (=200 km/s); so twice as fast. And galaxy C is even three times as far away from Earth’s point of view.
Now transfer this to a mathematical formula: which describes the so-called Hubble parameter.The Hubble constant is when you use the current age of the universe (i.e. 13.8 billion years). This Hubble parameter currently has a value (which is also confirmed by measurements in space) of about 70 kilometers per second per megaparsec (1 megaparsec equals about 3 million light-years).
So it seems to us that there are galaxies that move away from us at overlight speed.Light – as we have learned – always spreads in a vacuum at around 300,000 km/s. used to express the starting point of a movement.
But if the space expands faster and faster, there is a point somewhere where it expands “faster than the light”.Now the light must fly at a faster speed than it can reach itself.
Imagine climbing into one lake and being an experienced swimmer, then you can estimate how long it will take you to reach the other shore.But now you go into a river in the Alps. It flows faster than you can swim. You never manage to reach the opposite shore in this place!
The “light from the Big Bang” comes towards us at the speed of light; but at the same time everything flies away from us.So we are already here while the light is troting behind us!
This, in turn, is why we can’t observe galaxies far away, but only theoretically know about them, and why we can only see the nearby galaxies that only move away from us at the lower speed of light.
Ok, but this leads to the question: how quickly does a volume of space in which a galaxy is involved have to move away from us that the light of this galaxy on Earth no longer reaches us?
Logically, the volume of space must move away from us at the speed of light!The two light speeds do not rise to zero, but the light that reaches us is simply too slow for us to see and measure.
Light now emitted by galaxies beyond the event horizon (i.e. beyond the radius of 16 billion light-years) can never reach us on Earth because the space between the galaxy and us is simply expanding too fast.