Does the expansion of the Universe break the speed of light? - Big Think

And yet, when we look at the most distant of objects, their light has been traveling for no more than 13.8 billion years, but appears much farther away.

The most distant galaxy we’ve seen so far is presently 32 billion light-years away; the most distant light we see corresponds to a point presently 46.1 billion light-years away; and galaxies beyond about 18 billion light-years away can never be reached by us, even if we sent a signal at the speed of light today.

Here’s what everyone should know about the expanding Universe and the speed of light.

In other words, when we say “nothing can move faster than light,” we mean “nothing can move faster than light through space,” but that the motion of objects through space tells us nothing about how space itself will evolve?

You’ve likely heard that we live in an expanding Universe, and that we’ve measured the rate at which the fabric of space itself expands: the Hubble constant?

One, it’s not actually moving at that speed through space, but rather this is the effect of the space between objects expanding.

What’s important to recognize is that the expansion doesn’t have an intrinsic speed to it at all; space expands at a frequency: a speed-per-unit distance.

The light from distant objects does indeed get redshifted, but not because anything is receding faster than light, nor because anything is expanding faster than light.

However, we’re not measuring an actual speed; we’re measuring the cumulative effects of motions plus the effect of the expanding Universe.

When we say “the Universe is accelerating,” what we actually mean — and this is not what you’d intuit at all — is that if you watch the same object as the Universe expands, it will not only continue to increase in distance from you, getting farther and farther away, but the light that you receive from this object will continue to display an ever-increasing redshift, which makes it seem as though it’s accelerating away from you.

When we talk about the distance to an object in the expanding Universe, we’re always taking a cosmic snapshot — a sort of “God’s eye view” — of how things are at this particular instant in time: when the light from these distant objects arrives.

We know that we’re seeing these objects as they were in the distant past, not as they are today — some 13.8 billion years after the Big Bang — but rather as they were when they emitted the light that arrives today.

The farthest observed galaxy GN-z11, emitted its now-arriving light 13.4 billion years ago, and is located some 32 billion light-years away.

If we could see all the way back to the instant of the Big Bang, we’d be seeing 46.1 billion light-years away, and if we wanted to know the most distant object whose light hasn’t yet reached us, but will someday, that’s presently a distance of ~61 billion light-years away: the future visibility limit.

Any object presently beyond 18 billion light-years from us will still emit light, and that light will travel through the Universe, but the fabric of space will simply expand too relentlessly for it to ever reach us.

Nothing moves faster than light in an expanding Universe, and that’s both a blessing and a curse