An Infinite Past?

[robrecht]

... But on a side note, if a multiverse was really so different then there may be no real way to know what the actual properties are, therefore no real way to know if it exists.

http://www.scientificamerican.com/ar...llel-universe/

He goes on to describe how evidence might be found for the multiverse. I believe the search for (brane) collision evidence is now excluded by the magnitude of the recently discovered evidence for inflation. But there were other avenues of evidence being pursued. We saw above that Alan Guth and Anfrei Linde consider the recently discovered evidence for inflation to also imply a multiverse based on the models of inflation that are still viable.

[seer]

He goes on to describe how evidence might be found for the multiverse. I believe the search for (brane) collision evidence is now excluded by the magnitude of the recently discovered evidence for inflation. But there were other avenues of evidence being pursued. We saw above that Alan Guth and Anfrei Linde consider the recently discovered evidence for inflation to also imply a multiverse based on the models of inflation that are still viable.

Yes:

I think that the above would be credible evidence for a multiverse. But does getting us to a multiverse necessarily get is to an eternal past for matter and energy. Never mind the on going objection of infinite regression.

[robrecht]

Yes:

I think that the above would be credible evidence for a multiverse. But does getting us to a multiverse necessarily get is to an eternal past for matter and energy. Never mind the on going objection of infinite regression.

I don't know yet; that's what I'm here to find out. Hope springs eternal!

[robrecht]

Exactly! Thank you...

Oops. I was not so exact. I wrongly assumed you were quoting Vilenkin, but instead it seems you were quoting Lisa Grossman. She may have been ambiguous where Vilenkin is not ambiguous.

[seer]

Oops. I was not so exact. I wrongly assumed you were quoting Vilenkin, but instead it seems you were quoting Lisa Grossman. She may have been ambiguous where Vilenkin is not ambiguous.

Then read your own link:

The end of inflation is triggered by quantum, probabilistic processes and does not occur everywhere at once. In our cosmic neighborhood, inflation ended 13.7 billion years ago, but it still continues in remote parts of the universeself-contained bubble universe....

This picture of the universe, or multiverse, as it is called, explains the long-standing mystery of why the constants of nature appear to be fine-tuned for the emergence of life...

So we live in a "self-contained bubble universe", but the first "universe" is the larger cosmos where bubbles are still being formed. So Vilenkin does use it interchangeably.

[robrecht]

Then read your own link:

So we live in a "self-contained bubble universe", but the first "universe" is the larger cosmos where bubbles are still being formed. So Vilenkin does use it interchangeably.

Ah so, good point. It seems it is not so easy to talk about the multiverse. A universe here, a universe there, and pretty soon we're awash in some kind of mysterious multiverse!

[seer]

Ah so, good point. It seems it is not so easy to talk about the multiverse. A universe here, a universe there, and pretty soon we're awash in some kind of mysterious multiverse!

When I have listened to Vilenkin the "universe" he is often speaking of is the multiverse. Which is really just one big cosmos that spits out these smaller baby universes.

[shunyadragon]

When I have listened to Vilenkin the "universe" he is often speaking of is the multiverse. Which is really just one big cosmos that spits out these smaller baby universes.

Ther is nothing in Vilenkin's writings nor references you cited indicate this. He simply deals with the history of our universe and relates this to the formation of all possible universes.

[shunyadragon]

Then read your own link:

So we live in a "self-contained bubble universe", but the first "universe" is the larger cosmos where bubbles are still being formed. So Vilenkin does use it interchangeably.

No Vilenkin does not say this. No the greater cosmos (universe is not used interchangeably with what he calls bubble universes.

In the reference I cited from Vilenkin he state that beyond the visible limits at ~14 million years ago it was previous thought that beyond they used to there was just more universe, but now scientists consider there to something very different.

In other words beyond our universe, the greater cosmos is very different.

I may return with an exact quote.

[robrecht]

Then read your own link:

So we live in a "self-contained bubble universe", but the first "universe" is the larger cosmos where bubbles are still being formed. So Vilenkin does use it interchangeably.

When you quoted from my link, it automatically italicized the whole text. Now that I can see the text of the link on my computer, I see that Vilenkin italicized this first usage in his article of the term multiverse that he has been describing in the previous paragraphs. Thus, he describes this view of the universe actually containing multiple bubble universes and now calls it a multiverse. He's not really using the terms interchangeably.

[robrecht]

No Vilenkin does not say this. No the greater cosmos (universe is not used interchangeably with what he calls bubble universes. ...

I agree.

[JimL]

First no, the idea that this universe began is not controversial. That is not where the argument comes in. BGV theorem is the theory for an eternally expanding universe. They are not speaking of this universe since neither Vilenkin no Guth are claiming that this universe will expand for ever creating smaller "bubble" universes. But look again at my quote:




They suggest, by their math, that the expansion could go on eternally into the future. The bubbles are the new universes being formed (within the multiverse) - the question is; can this bubble forming process not only go forward in time, eternally, but also go backwards in time eternally. The answer according to the theorem is no. And without this bubble forming process you have no universes being created. So even if you had some kind of multiverse it would not be producing anything. And if you watch the video, early on, Vilenkin speaks of this bubble forming process and makes it clear that that is the process that can not be past-eternal.

It isn't the bubbles that are past eternal, how could they be, they each begin to exist, the bubbles, or pocket universes that form is that which is termed the multiverse, but the mutiverse is contained within the Greater Cosmos which itself would be eternal into the past.

[Tassman]

Tass, then present it, where is any concrete evidence for an eternal physical past? There is zero. Sure, like your link showed, there are ideas, but even there, there are contradictory theories with no actual evidence that gets us to an eternal past.

I've acknowledged several times that there is no empirically verified evidence at this time. However, to repeat, this is not the same as your misleading and oft repeated claim of: "zero evidence". In fact there are several competing hypotheses, each supported by a body of evidence, based upon the

That is absolutely false Tass. The eternal inflation theory is a multiverse theory.

Multiverse theory is reinforced by inflation theory. But inflation theory is a not a multiverse theory as such.

An ever expanding cosmos that bubbles up smaller universes like ours. Though inflation can be eternal into the future it "can not" be eternal into the past. The universe forming process (bubbles) is not past eternal. Vilenkin makes that perfectly clear, and the only reason you reject it is because you are completely bias.

that make up the multiverse, (Vilenkin) NOT

[Leonhard]

that make up the multiverse, (Vilenkin) NOT

I'm curious do you have any sources from Vilenkin that justifies this reading of him? Because the way I got his view was that the inflationary multiverse started in some sort of quantum nucleation event at t = 0, in some sort of vacuum.

His theorem is clearly applicable to any spacetime which undergoes expansion over time on average. Since this is true of nearly all space times who aren't collapsing, where do you get that is only about the constituents?

Whether its our bubble, or the false vacuum betweeen the bubbles the argument would still apply: particles would blue-shift infinitely in finite proper time.

Physics doesn't allow that.

However since the only two key assumptions were a past-complete universe and an on average expansion of the universe greater than zero and not tending towards zero sufficiently fast (and this is true in all inflationary models). Then the only sensible move is to give up the idea of a past-complete universe.

Its the simplest move to deny past-completeness so use Ockhams Razor (or Sobels Lightsaber if you're into the Bayes Epistemology cult). Its always simpler to deny something if accepting entails all sorts of weird new entities, such as specialised spacetimes, or physics with just-the-right laws, etc to save a past infinite universe.

Am I missing something Tassman?

[seer]

When you quoted from my link, it automatically italicized the whole text. Now that I can see the text of the link on my computer, I see that Vilenkin italicized this first usage in his article of the term multiverse that he has been describing in the previous paragraphs. Thus, he describes this view of the universe actually containing multiple bubble universes and now calls it a multiverse. He's not really using the terms interchangeably.

Yes he is, from you link:

This picture of the universe, or multiverse, as it is called, explains the long-standing mystery of why the constants of nature appear to be fine-tuned for the emergence of life...

And:

The end of inflation is triggered by quantum, probabilistic processes and does not occur everywhere at once. In our cosmic neighborhood, inflation ended 13.7 billion years ago, but it still continues in remote parts of the universe

Is the universe above where bubbles are forming, the multiverse?