The Universe' Size

I read recently in this well written article to creationists that the universe is estimated to be 46 billion lightyears from end to end. I, admittedly, am terrible at math and worse at spatial cognition, but I was thinking that the universe’ diameter should only be as much as twice it’s age, or 27.6 billion lightyears (the age being the radius of the universe), assuming nothing travels faster than light. The universe seems to be expanding. Is it doing so at (now) faster than light? Or am I just misunderstanding something?

1 Like

Ha!

3 Likes

I think this is where the difference lies in your estimate and what he writes. Here is another article he wrote explaining that the universe does indeed expand faster than the speed of light and that’s OK:

Or there are a handful of interesting videos (I don’t have time to watch at the moment but found this one) that explain some of this:

5 Likes

During inflation the universe is thought to have expanded faster than the speed of light. My understanding is the fabric of the universe itself is not included in the standard claim of nothing (“no material objects”) can travel faster than light from relativity. So it can expand faster than light.

4 Likes

Aye, spacetime is physical, but has no mass, no energy. It isn’t subject to relativity. Wow!

2 Likes

I’ll definitely check out the videos. This is something I’ve wondered to at random times, but was always busy to look it up at the moment. I can’t remember what it was but I asked a question and it somehow landed me getting snark. It was something similar and was like if a star is 8 billion light years away, and we were able to travel from one end of its light to the other end , since it was going in all direction, would that mean it would take 16 billion years to travel that distance? Then I asked if the universe is only roughly 14 billion years old, would the speed of light from one end to the other at this moment be 28 billion light years wide and if so, how are there these stars in it like Earendel 28 billion light years away.

1 Like

The basic reason for the disparity is that the time-based distance is an average over the period that the light was in transit, thus (taking Earendel as an example), if the light started 4 GLy away, it might take 13 Gy to get here, and by now the total distance is something like 25 Gy. So, we aren’t actually seeing it at a distance of 25 Gy, we are seeing it as it was 13 Gy ago and 4 GLy away.

5 Likes

Yes, that hurts my head, but thank you. :slight_smile:

3 Likes

Agreed, but considering whether space is infinitely divisible isn’t that mind numbing.

And it doesn’t matter whether it is or isn’t :grinning:

Very cool. Thanks very much Matthew!

ssssOOOO, what (intrinsically?) drives the accelerating expansion of spacetime, which does not exist independently of matter. Wherever matter exists it occupies spacetime perichoretically which intrinsically accelerates in all directions faster than matter does mainly radially? What’s its limit? The dilution of heat dead matter?

1 Like

A possibly useful analogy is the fact that I could be riding an airplane traveling at 700 km/hr and walk forward along the aisle at 2 km/hr. My net speed would be 702 km/hr, but that doesn’t mean that I can walk at 702 km/hr. Likewise, galaxies aren’t moving faster than light, but the combined effect of their motion and the expansion of the universe means that the distance between them and us could increase faster than light.

5 Likes

It is useful, but it is really different than the question in the OP. It was “why is the universe bigger than twice the age of the universe” (13.8b + 13.8b = 27.6b ly, but it is actually 46 bly across.) The answer from the gallery is that space-time is not constrained by relativity, because it has no mass, and it is actually expanding at greater than light speeds. And, yes, my head still hurts. :slight_smile:

1 Like

The name given to that force is dark energy.

On a local level, the current rate of expansion is very small and is swamped by gravitational forces, so you won’t see a local cloud of matter being pulled apart by expansion. Even our local supercluster of galaxies is orbiting around a center of mass instead of rocketing out in all directions due to expansion.

1 Like

Aye. Isn’t dark energy just a placeholder for the power, if power is needed, warranted, for the utterly unknown, indefinable principle of omnidirectional accelerating expansion of spacetime. For some sort of negative gravity analogy more powerful than gravity. Is that the only rational - and it doesn’t have to be rational at all - possibility? That as the universe expands, dragging spacetime with it, the power of gravity diminishes and the constant(? YES!) power of negative gravity, i.e. dark energy, expands spacetime, but has no significant effect on matter made of the 61 elementary particles (baryons and leptons, fol-da-dee) of the standard model?

From my less than perfect understanding of physics . . .

I don’t know if this is a poor comparison, but gravity is the placeholder name for the force that bends spacetime around mass and causes masses to be attracted to one another. Dark energy and gravity aren’t that different in this context.

It is my understanding that dark energy expands spacetime itself. Spacetime isn’t being dragged anywhere. It isn’t until you get to massive distances (like those between galaxy clusters) that the cumulative expansion of all that spacetime between the clusters is finally stronger than the gravitational force between those very distant galaxies. The effects of expansion at the atomic or molecular level is completely ignorable, at least at present.

However, the rate of expansion is increasing. If this continues at an exponential rate then there will be a time in the very distant future where the rate of expansion is enough to tear molecules and atoms apart.

1 Like

Ah HA! The former is nice and minimal. Wherever light goes, spacetime goes with it. It’s meaningless beyond it; doesn’t go before it.

And that’s nice too. Not rational at all is it?!

I believe that that is the radius, and the diameter is 93 GLy.

2 Likes

If by irrational you mean poorly comprehended by us limited humans and counter to our biased intuitions, then yes.

2 Likes

Biased? I was thinking today about the time you thought I was pranking you when I was getting you to consider the appearance of particles from nothing and how it was something that just happens or it was caused by something that doesn’t happen.

“Let your conversation be always full of grace, seasoned with salt, so that you may know how to answer everyone.” -Colossians 4:6

This is a place for gracious dialogue about science and faith. Please read our FAQ/Guidelines before posting.