At the Big Bang, matter must have moved faster than the speed of light, otherwise we wouldn’t be able to see galaxies that are 12 billion light years away from us, would we?

Corey Houghton
By Corey Houghton
Questions and Answers

I am intrigued by the origin of the universe, the theory of relativity, black holes, etc, and also read many books about it. But I haven’t found a logical explanation to my question anywhere. The speed of light is the ultimate maximum. The universe is about 13.5 billion years old. I therefore do not understand that we now receive light from distant galaxies that has taken 12 billion years to reach us. Then this matter must have moved away from us faster than light at the Big Bang? But you can’t go faster than light. So … ?

Asker: Luke, 48 years old

Answer

THE’ speed of the expanding yellowal does not exist. The bulge follows from Hubble’s law, which states that the galaxies are moving away from each other at a speed proportional to their distance from each other. Twice as far means twice as fast.

It is indeed possible for two points in space to move away from each other at a speed greater than the speed of light. After all, the expansion is an expansion of space itself, relative to that space the galaxies actually stand still. It is therefore not a real Doppler effect: it is not the ambulance that is moving away from us, but the street that is getting longer! Within that expanding space, physics applies: nothing can move in that space with a speed greater than the speed of light.
We do not see points that move relative to us at a speed greater than the speed of light, because the distance that the path to them becomes longer is greater per unit time than the distance that the signal can travel. They are beyond our horizon. If expansion slows down, they could end up within our horizon.
The big bang corresponds to an expansion speed equal to the speed of light: what comes to us moves away just as fast as it comes to us… The redshift (shift of light to longer wavelengths) is then infinite, so we see nothing at all.

At the Big Bang, matter must have moved faster than the speed of light, otherwise we wouldn’t be able to see galaxies that are 12 billion light years away from us, would we?

Answered by

prof. Christopher Waelkens

Astronomy

Catholic University of Leuven
Old Market 13 3000 Leuven
https://www.kuleuven.be/

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