The Edge of the Universe

[Chimera]

Assuming the Big Bang, that the Universe popped out like a rapidly expanding bubble in all directions, what would the edge of the Universe look like?

I’m thinking that even as mass coalesced from the primorial quantum ooze and formed stars, green clovers and galaxies, even if that expansion of the Universe slowed, wouldn’t there still be what essentially amounts of an expanding particle wavefront of neutrinos, photons and other high energy, light speed particles expanding at light speed in every direction? And even if these particles are virtually massless, wouldn’t that still be a tremendous amount of mass/energy pushing outward in all directions at light speed?

[Riemann]

The Big Bang did not happen at a single point in preexisting space. It happened everywhere. The expanding universe is not a bubble with an edge in the way that you envision.

[k9bfriender]

There is an expanding particle wavefront of neutrinos, photons and other high energy, light speed particles expanding at light speed in every direction, and that wavefront is passing by us right now.

[Chronos]

And was also passing us yesterday, and a billion years ago, and ten billion years ago, and will also be passing us ten and a hundred billion years from now.

[Chimera]

@Riemann

The Big Bang did not happen at a single point in preexisting space. It happened everywhere. The expanding universe is not a bubble with an edge in the way that you envision.

That would be a wrong assumption. Everything that ever was, is and will be is in that bubble. I’m just asking what is happening at the edges.

So let’s back off the “you’re wrong” and start providing actual, productive answers, eh?

[Riemann]

@k9bfriender

There is an expanding particle wavefront of neutrinos, photons and other high energy, light speed particles expanding at light speed in every direction, and that wavefront is passing by us right now.

But describing it as an “expanding particle wavefront” may tend to reinforce the misconception in the OP. The origin of this radiation is a sphere centered on us, not a point. This radiation originated everywhere in the universe, not at a single point in preexisting space (and somewhat later than the Big Bang, but that’s another matter). The source of the radiation that happens to be passing us at a given moment is just a function of our time and place in the universe.

[Riemann]

@Chimera

That would be a wrong assumption. Everything that ever was, is and will be is in that bubble. I’m just asking what is happening at the edges.

So let’s back off the “you’re wrong” and start providing actual, productive answers, eh?

If you think there are edges to the expansion of space, your conception of cosmology is indeed wrong.

I am trying to search out some prior threads with good explanations rather than just telling you your are wrong, but give me a few minutes - the search function on here is not the best.

[k9bfriender]

@Riemann

But describing it as an “expanding particle wavefront” may tend to reinforce the misconception in the OP. The origin of this radiation is a sphere centered on us, not a point. This radiation originated everywhere in the universe, not at a single point in preexisting space (and somewhat later than the Big Bang, but that’s another matter). The source of the radiation that happens to be passing us at a given moment is just a function of our time and place in the universe.

I get that, and Chronos subsequently and correctly added to what I said. But it is true that the “explosion” of the big bang is passing by us right now, and as he said, yesterday and tomorrow, and all the yesterdays and all the tomorrows.

[Stranger_On_A_Train]

@Chimera

Assuming the Big Bang, that the Universe popped out like a rapidly expanding bubble in all directions, what would the edge of the Universe look like?

There is no edge or center of the universe in any privileged frame of reference. There is the cosmological (or comoving) horizon which defines the limits of the observable universe for us on Earth, but somewhere out there could be an intelligent observer for whom our planet and sun are at the limit of their obsevable universe, approximately 46.5 Bly away in comoving distance (as the interstellar crow flies, so to speak). They wouldn’t literally see our solar system because they’d be seeing light from over 13 Byr ago, but they could see the precursor galaxies forming to generate the heavier elements that would one day make up our galaxy and planetary system.

Stranger

[k9bfriender]

@Stranger_On_A_Train

There is no edge or center of the universe in any privileged frame of reference. There is the cosmological (or comoving) horizon which defines the limits of the observable universe for us on Earth, but somewhere out there could be an intelligent observer for whom our planet and sun are at the limit of their obsevable universe, approximately 46.5 Bly away in comoving distance (as the interstellar crow flies, so to speak). They wouldn’t literally see our solar system because they’d be seeing light from over 13 Byr ago, but they could see the precursor galaxies forming to generate the heavier elements that would one day make up our galaxy and planetary system.

Stranger

So waving to them is pointless then?

[cmyk]

@k9bfriender

So waving to them is pointless then?

Not to whomever’s around 13 billion years from now.

[octopus]

@Riemann

If you think there are edges to the expansion of space, your conception of cosmology is indeed wrong.

I am trying to search out some prior threads with good explanations rather than just telling you your are wrong, but give me a few minutes - the search function on here is not the best.

So the region before the big bang was unbounded?

[k9bfriender]

@cmyk

Not to whomever’s around 13 billion years from now.

That’s the downside. As the universe expands, more and more of what is now the visible universe will pass beyond the cosmological horizon. the light leaving our planet now will never reach them.

[dtilque]

@k9bfriender

I get that, and Chronos subsequently and correctly added to what I said. But it is true that the “explosion” of the big bang is passing by us right now, and as he said, yesterday and tomorrow, and all the yesterdays and all the tomorrows.

And add to that that it applies equally everywhere in the universe. Everywhere sees the BB (or more exactly, the light emitted 380,000 years after the BB) in all directions. And everywhere has always (well, since it was emitted, of course) seen it and will always see it in all directions. No exceptions, there’s no edge where they see it from less than every direction.

[k9bfriender]

@dtilque

And add to that that it applies equally everywhere in the universe.

Awww, I thought we were special

Everywhere sees the BB (or more exactly, the light emitted 380,000 years after the BB) in all directions. And everywhere has always (well, since it was emitted, of course) seen it and will always see it in all directions. No exceptions, there’s no edge where they see it from less than every direction.

That is not to say that we know in any way definitively what lies beyond what we can see. It’s pretty sure that it is pretty much the same for some distance beyond the cosmological horizon, but it is possible that this happened to be a patch of the universe that inflated in a smooth and flat fashion, further out could have played out differently.

[Riemann]

@octopus

So the region before the big bang was unbounded?

I’m not considering any notion of “before the big bang”.

Many descriptions of cosmology fail to clarify the distinction between our observable universe and the entire universe. The observable universe is indeed bounded by a sphere, centered on us, that shrinks back to a point if we look back in time to the limit of the Big Bang. This leads to the misconception that the entire universe started at a point, and is bounded by a spherical edge, expanding in preexisting space.

Although the entire universe may not be infinite, I think it’s best to start with an assumption that it is - because if your conception of cosmology can’t accommodate that, you probably have some misconceptions in there.

I think the 1-dimensional “ants on a stretchy band” model is probably the best analogy. The expansion of space is the band stretching, meaning that ants that are locally stationary on the band move further apart. But assume that the band is infinite, just goes on forever without any ends. It’s not entirely clear quite what that means, but I think it clarifies some aspects of the model. Looking forward in time, the band expands, making points further apart; looking back in time, it contracts, making points closer together. But it has no ends, it just disappears off into infinity however close together or far apart things become.

Now, if you consider the observable universe for a particular ant standing at one particular place on the band, that just represents the line-segment of the band centered on that ant. And if you look back in time, that segment shrinks, tending to the limit of a point centered on that ant at the Big Bang. But there’s nothing special about that one point - it’s just defined by where that one ant happens to be standing. More generally, looking back in time toward the Big Bang is not the process of shrinking the entire band to any one particular point, it is the process of all points on this infinitely long band tending to become mutually closer to one another - while the total extent of the band remains infinite, it has no ends. And the Big Bang itself is the undefinied limit where the distance between any two points on the infinitely long band approaches zero.

A singularity is not the same thing as a “point in space”. A singularity is the infinity-times-zero limit where the model breaks.

The bottom line is that if you haven’t somehow got to grips with
(a) there are no edges to the expansion of space;
(b) the Big Bang happened everywhere
then you need to keep working on your understanding to find an analogy that works for you.

[Asympotically_fat]

@k9bfriender

That’s the downside. As the universe expands, more and more of what is now the visible universe will pass beyond the cosmological horizon. the light leaving our planet now will never reach them.

This both is and isn’t correct:

The particle horizon (aka cosmological horizon) which is the limit of the observable Universe, expands faster than a comoving volume meaning it takes in more galaxies. This is a generic feature of particle horizons*

Galaxies are leaving the cosmological event horizon which is the limit of what happens at the current cosmological time what we will be able to see in the future. This is a generic feature of cosmological event horizons*

*If the Universe is compact several copies of the same galaxy may be observable and it is one of those copies that enters/leaves. The Universe needn’t have either type of horizon and the existence of one horizon isn’t dependent on the other’s existence

[k9bfriender]

@Asympotically_fat

This both is and isn’t correct:

The particle horizon (aka cosmological horizon) which is the limit of the observable Universe, expands faster than a comoving volume meaning it takes in more galaxies. This is a generic feature of particle horizons*

Galaxies are leaving the cosmological event horizon which is the limit of what happens at the current cosmological time what we will be able to see in the future. This is a generic feature of cosmological event horizons*

*If the Universe is compact several copies of the same galaxy may be observable and it is one of those copies that enters/leaves. The Universe needn’t have either type of horizon and the existence of one horizon isn’t dependent on the other’s existence

Sorry, I did mean the cosmological event horizon, but I was focused on the difference between it and the black hole event horizon that I neglected to put that word in.

[Chimera]

@Riemann

The bottom line is that if you haven’t somehow got to grips with
(a) there are no edges to the expansion of space;
(b) the Big Bang happened everywhere
then you need to keep working on your understanding to find an analogy that works for you.

You know, this is why I’ve struggled with the idea of asking this on this board. Because instead of being gentle and informative, we have people like you on this board who fall back to telling people they’re wrong and coming all too close to being insulting, mocking and completely less than helpful.

Do better.

[Napier]

I think there’s a theory that there was a “before the big bang” in a five dimensional universe now forever closed to us, and that we are the “before the big bang” for numerous new one-dimensional universes that, from our point of view, begin at the bottom (to speak somewhat poetically) of the black holes in our universe. In this theory universes cascade below one another through black holes and each descending generation has two fewer geometrical dimensions than the one above. They are truly “below” in the sense that matter passes from one layer to the next by falling into black holes. This part is probably wrong, because it just sounds too neat and simple, but I vaguely recall the whole deal started with an eleven dimensional universe.

I wondered if expanding space today corresponds to stuff continuing to fall into the black hole above us. But that sounds about as sophisticated as that false equivalency between solar systems and atoms. Anyway, all the turtles on the way down have fewer and fewer dimensions.