How big was the universe one second after the Big Bang?

Let’s say you were there to witness the Big Bang. What did the universe look like one second later?

Scientists yammer on and on about a singularity and leptons and hadrons and quarks and anti-matter and so forth, but I’m not talking about the sub-atomic stuff; I’m talking about the visible stuff. From your perspective, wouldn’t it have looked to you like the universe simply and instantly appeared all around you: impossibly large …blinding light … deafening noise… insane heat … and the leading edge would have already been almost incomprehensibly far away (assuming it stopped one second after it started.)

Or do I have that wrong?

First of all, I’m not sure the universe ever had an edge (the physics guys will come in to to explain soon, and I’ll get a headache, as always).

Second of all, as the universe can’t expand at faster than the speed of light, then it probably would have expanded by 1 light second, or 186,282 miles.

But the universe can expand faster than light. In fact it is expanding faster than light right now. That’s why we will only ever see a tiny fraction of the universe. Beyond a certain point the galaxies are moving away from us faster than their light is moving towards us, so the light never reached us.

It takes an infinite amount of energy to *accelerate *an object to light speed, but the various parts of the universe were *created *moving away from each other at those speeds, so no acceleration required.

I found a website that says that in the lepton epoch (1-10 seconds after the Big Bang), the universe was about 1000 times the size of our solar system.

My understanding is that the universe was COMPLETELY opaque for approximately 380,000 years after the big bang, so you wouldn’t see anything at all (or it would just be nothing but white) if you were there to witness it.

According to this page, by 1 second the universe was roughly the size of our solar system.

I don’t think concepts like deafening noise and blinding light make much sense at that point. As I understand it there are no atoms yet, and the universe is opaque.

eta: ninja’d, but I’ll leave the link.

Special relativity would say otherwise. If I am moving west at 70mph, and you are moving east at 70mph, our relative speed would be 140mph, the relative speed at which we are moving away from each other. But this simple sum only works up to a point (many thousands of mph) before it start to curve downward. If we are moving in opposite directions each at two-thirds the speed of light, our relative speed adds up to a number that is less than the speed of light. This is where the famous time dilation effect comes in. Our speeds are correct, but the relative rate at which time passes for each of us with respect to the other changes so that the light speed limit is observed.

That holds for objects moving within the universe, but the expansion of the fabric of space-time itself is not bound by relativity.

What you are overlooking is that the objects are *not *moving within space. The space between them is increasing. So long as the space in between two objects is increasing faster than the distance that light can travel in the same time, then light can never pass between the two objects.

IOW, you are assuming that the objects start out with, say, 5 billion light years of space separating them, say . Then the objects start moving apart, increasing the intervening space through acceleration until they are now 15 billion light years apart. But that’s not correct.

The reality is that the objects started out with 5 billion light years between them but at present the amount of space between them has increased to 15 billion light years without the objects ever accelerating. That change in distance has been achieved by an increase in the amount of space in the universe, not by acceleration. Or to put it another way, the objects started out with 5 billion light years between, but because the universe is expanding each intervening light year has become 3 light years. Each intervening light year has become longer, but the objects have never accelerated.

As a result, the objects are now receding from each other faster than the speed of light. Light being emitted by the two objects right now can never pass between them, because by the time a photon travels one light year, the distance between the objects will be >1 light year. The speed of light remains constant and nothing is accelerating faster then light, so no violation of relativity. But the amount of intervening space is increasing faster than 1 light year/year.

I was going to suggest the Wikipedia article onHubble Volume, but it’s not all that illuminating.

Or what Richard Pearse said.

It depends on what shape the universe is, and whether or not you are talking about all of the universe or only the observable universe. Pretty much everything talked about so far has been about the observable universe, not the entire universe. As for the entire universe, as far as I can tell the most favored theory at the moment holds it to be “flat” and infinite in size; so it would have been infinite one second after the Big Bang as well.

Also, you wouldn’t have been able to see anything if you were there even if you were indestructible; it was much too dense for light to travel.

The Universe is either finite or infinite, and we don’t know (and probably can’t know) which. If it’s infinite, then it has always been infinite, and always will be infinite. If it’s finite, then it was much smaller at t = 1 s than it is now, but it’d still be quite huge, since that’s actually pretty late in the Universe’s history. Specifically, it’s after the era of inflation, a time when the Universe grew exponentially with a very short time scale, and which ended at somewhere around 10^-32 seconds.

Good point!

I was rather startled the first time I read that, since I’d always assumed that the universe was essentially a point source at the singularity. But if we can believe Brian Greene, it ain’t necessarily so.

Also (again, assuming that Greene accurately captures current consensus), the folks who say the universe can expand faster than the speed of light are correct.

If I understand it correctly, that’s one of two possible reasons, the other being the possibility that it was infinite. But I wonder whether there’s any evidence that all we can see is a tiny fraction. The odds are probably in favor of that (when a quantity is completely unknown, what’s it’s relation to a fixed value? Hmmm …). But I think there’s even a possibility that we can see it all.

Perhaps someone else can be more specific or find a cite, but I seem to recall someone proving the existence of matter outside the visible universe by looking at the effects of gravity on some of the things we can see.

I saw this theory recently on Through the Wormhole with Morgan Freeman, where it appears that much of the visible universe is drifting slightly in a direction, implying that there is another “universe” out there attracting it. Very interesting. I forget the name of the leader of this discovery team that is obviously someday going to be a household name if proven true.

Of course, if the universe rate of expansion and these extra “universes” (other big bangs) exist with roughly the same physical laws, then someday they universe may collide!

The above is written by someone who only knows enough to be dangerous.

Thanks, didn’t know that!

As a dangerous one myself, I think this falls into two categories here.

  1. stuff that’s simply beyond our sphere of direct observation (based on speed of light: it’s over the horizon). Not too much worry about that stuff, assuming it’s a lot like the stuff we can see. And the biggest factor about what we can see is that everything looks like it’s the same as here, as far as we can see.

  2. other bangs. My guess is, there’s no shared spatial reference – no concept of a distance between them. If so, there’s no chance of a collision.

Of course, there are always more categories, even when one of the categories is “everything else”. If we believe Goedel, that is. Even if Goedel was wrong, I still think this part is right!


What I remember hearing on TV or reading: regardless of whether it’s finite or infinite, the universe has no edge(s). If one could travel long enough in a straight line, they would end up where they started.

Why not the same size as it is now?

Cuz of expansion. Whatever the finitude/size/shape of the universe as a whole, we do know that light from distant objects in the visible universe is exhibiting a Doppler shift consistent with increasing distance. Consequently, things in the universe are moving away from each other, so the whole shebang (at least the part we observe) is definitely getting bigger.

Of course, if what you meant is that, as Chronos noted, the universe might be infinite and if so then it always was infinite and hence is the same “size” now as it was one second after the Big Bang, that’s true. But the observed expanding part that we’re in, at least, has definitely gotten bigger since then.

For some reason it is a real bitch finding detailed information on the size and rate
of expansion of the early unverse. If I screwed up the arithmetic below hopefully
one of our specialists can fix it.

This siteinforms us that the Universe was about the size of a grapefruit at the end
of the Inflationary Epoch ~10^-36 seconds after the Big Bang. Since the IE is thought
to be the only period during which the Universe expanded at faster than the speed of light,
and since the fundamental forces had decoupled by 10^-6 (1 millionth) seconds then
at one second visible light should have travelled apprx. 1-(1 millionth) x 299792 meters,
or about 22% the diameter of the Sun. A star that size would be clearly visible from Earth.
However, the Sun’s temperature is about 6000C, whereas at age one second the universal
temperature was one trillion degrees. Even if it were meaningful to hypothesize being
able to view the Universe from outside, at age one second it would be blinding to human eyesight.

A nitpick. The cosmic redshift is not a Doppler shift. It’s caused by the stretching of space during the light’s long transit to Earth, not by the relative velocity of the distant emitter.