Universe or Multiverse?

[tmazanec1]

Is our observable universe out to the Hubble Radius all there is, or is it reasonable to postulate that there are other such volumes, with perhaps different laws and constants of nature?

[Formless]

"INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

(cookie if you know where the quote comes from. Note: the cookie is a lie)

Just think about it for a moment: there are multiple models for how the big bang worked with different working assumptions of what came before it. On top of that, there are multiple interpretations of quantum mechanics, the two most famous (the multi-worlds interpretation and the Copenhagen interpretation) being considered by most physicists to be absurd when taken on their own. There are multiple models of particle physics, multiple versions of string theory, multiple Unified theory alternatives besides, and each one has something different to say on the issue. So basically, not enough data to rule it out, not enough data to rule out the null hypothesis (i.e. one universe).

But hey, even if there is only one universe, its huge. The Hubble radius doesn't cover a fraction of its size, its simply the upper limit on how far out we can see. Go out beyond our Hubble radius, and you might as well be in a different universe than Earth resides in.

[Lord of the Abyss]

There does appear to be something beyond the observable universe pulling on the matter we can see.

Mysterious New
The galaxy cluster 1E 0657-56 (known as the Bullet Cluster) lies 3.8 billion light-years away. It's one of hundreds that appear to be carried along by a mysterious cosmic flow.
NASA/STScI/Magellan/U.Arizona/D.Clowe et al.
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As if the mysteries of dark matter and dark energy weren't vexing enough, another baffling cosmic puzzle has been discovered.

Patches of matter in the universe seem to be moving at very high speeds and in a uniform direction that can't be explained by any of the known gravitational forces in the observable universe. Astronomers are calling the phenomenon "dark flow."

The stuff that's pulling this matter must be outside the observable universe, researchers conclude.

When scientists talk about the observable universe, they don't just mean as far out as the eye, or even the most powerful telescope, can see. In fact there's a fundamental limit to how much of the universe we could ever observe, no matter how advanced our visual instruments. The universe is thought to have formed about 13.7 billion years ago. So even if light started travelling toward us immediately after the Big Bang, the farthest it could ever get is 13.7 billion light-years in distance. There may be parts of the universe that are farther away (we can't know how big the whole universe is), but we can't see farther than light could travel over the entire age of the universe.

Mysterious motions

Scientists discovered the flow by studying some of the largest structures in the cosmos: giant clusters of galaxies. These clusters are conglomerations of about a thousand galaxies, as well as very hot gas which emits X-rays. By observing the interaction of the X-rays with the cosmic microwave background (CMB), which is leftover radiation from the Big Bang, scientists can study the movement of clusters.

The X-rays scatter photons in the CMB, shifting its temperature in an effect known as the kinematic Sunyaev-Zel'dovich (SZ) effect. This effect had not been observed as a result of galaxy clusters before, but a team of researchers led by Alexander Kashlinsky, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md., found it when they studied a huge catalogue of 700 clusters, reaching out up to 6 billion light-years, or half the universe away. They compared this catalogue to the map of the CMB taken by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite.

They discovered that the clusters were moving nearly 2 million mph (3.2 million kph) toward a region in the sky between the constellations of Centaurus and Vela. This motion is different from the outward expansion of the universe (which is accelerated by the force called dark energy).

"We found a very significant velocity, and furthermore, this velocity does not decrease with distance, as far as we can measure," Kashlinsky told SPACE.com. "The matter in the observable universe just cannot produce the flow we measure."

Inflationary bubble

The scientists deduced that whatever is driving the movements of the clusters must lie beyond the known universe.

A theory called inflation posits that the universe we see is just a small bubble of space-time that got rapidly expanded after the Big Bang. There could be other parts of the cosmos beyond this bubble that we cannot see.

In these regions, space-time might be very different, and likely doesn?t contain stars and galaxies (which only formed because of the particular density pattern of mass in our bubble). It could include giant, massive structures much larger than anything in our own observable universe. These structures are what researchers suspect are tugging on the galaxy clusters, causing the dark flow.

"The structures responsible for this motion have been pushed so far away by inflation, I would guesstimate they may be hundreds of billions of light years away, that we cannot see even with the deepest telescopes because the light emitted there could not have reached us in the age of the universe," Kashlinsky said in a telephone interview. "Most likely to create such a coherent flow they would have to be some very strange structures, maybe some warped space time. But this is just pure speculation."

Surprising find

Though inflation theory forecasts many odd facets of the distant universe, not many scientists predicted the dark flow.

"It was greatly surprising to us and I suspect to everyone else," Kashlinsky said. "For some particular models of inflation you would expect these kinds of structures, and there were some suggestions in the literature that were not taken seriously I think until now."

The discovery could help scientists probe what happened to the universe before inflation, and what's going on in those inaccessible realms we cannot see.

The researchers detail their findings in the Oct. 20 issue of the journal Astrophysical Journal Letters.

"INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

(cookie if you know where the quote comes from. Note: the cookie is a lie)

The Last Answer, by Isaac Asimov.

[Simon_Jester]

But hey, even if there is only one universe, its huge. The Hubble radius doesn't cover a fraction of its size, its simply the upper limit on how far out we can see. Go out beyond our Hubble radius, and you might as well be in a different universe than Earth resides in.

Well. It's theoretically possible to fly to a point that is presently outside our Hubble radius; it would just take many many billions of years.

Where you really get into "might as well be in a different universe" territory is:

Given the rate of expansion of the universe, new distance gets added between any two points at a certain rate, proportionate to the distance already between the two points. If two points are far enough apart, new distance is added between them at a rate of over 300,000 kilometers per second... which means that even travelling at light speed, you cannot go from one of those points to the other.

Now then you are looking at a point that might as well be in another universe, because you can't get there from here.

(I am not confident of my ability to calculate this radius without giving it a lot of thought. Ask a cosmologist)

[Rabid]

Just some kind of nitpick / useless trivia...

From what I heard, due to the expansion of the universe, the Hubble Radius is, effectively, not of 13.7 billions light-year, but more about 45 billions light-year.

This is due to the fact that in the time taken by the light to come from "distant part of the universe / origin of cosmos", the expansion of the universe made the "distant part of the universe / origin of cosmos" move in the other direction faster than the speed of light relatively to us. This also mean that if light can come from farther away as time pass, it also mean that space expand much farther away in the same time. I'll let you meditate on what that ultimately mean...

Hint : In [UNKNOW] billions of year, our galaxy will effectively be "the only one in the universe". From our point of view at least...

[Alferd Packer]

The Last Answer, by Isaac Asimov.

The Last Question. Asimov did indeed write a short story titled The Last Answer about 25 years after The Last Question. They cover somewhat similar themes, but The Last Answer is a rather average tale compared to the other.

Aaaaanyway, to the OP, since the universe is everything that exists, to postulate that there is something outside, above, or beyond it just isn't reasonable. Sure, it's entertaining, but it doesn't really get you anywhere.

[Serafina]

Even if there are other universes, they would not exist for all intents and purposes, since we could not interact them in any way. If we CAN interact with them, then they are arguably part of our universe.

[Lord of the Abyss]

Even if there are other universes, they would not exist for all intents and purposes, since we could not interact them in any way. If we CAN interact with them, then they are arguably part of our universe.

Actually, no; I understand that in theory it's possible for another universe to interact with ours. However it would be bad for us since that interaction would consist of a "domain wall" (a 2 dimensional relative of a cosmic string; a huge spacetime defect) where the two universes met; like the membrane between two soap bubbles. Since such a domain wall would be ridiculously massive it would cause a cosmological scale flow of matter towards it; one of the farther out speculations for the cause of that previously mentioned "dark flow" is another universe intruding into ours somewhere beyond the observable universe.

And according to some theories our universe budded off from another universe; since without it we wouldn't exist that certainly does mean it mattered that the other universe exists.

[Eternal_Freedom]

My physics lecture told us some strange idea's his colleagues had dabbled with a year or so ago: that there ae indeed multiple universes that interfere with our own. This apparently ratioanlises the wave/particle duality by saying that they are individual particles, but the inteference pattern is from all the other possible particles in their own universe intefereing with the one we see in our universe.

The general response of my group was "while it's interesting as an academic discussion what's the point in worrying about it?"

EDIT: Sorry, should have included that this multi-universe inteference idea would apparently remove it from quantum physics and result in a classicly mechanical universe after all. Which is somewhat appealing.

[dragon]

Then there's this.

In the most recent study on pre-Big Bang science posted at arXiv.org, a team of researchers from the UK, Canada, and the US, Stephen M. Feeney, et al, have revealed that they have discovered four statistically unlikely circular patterns in the cosmic microwave background (CMB). The researchers think that these marks could be “bruises” that our universe has incurred from being bumped four times by other universes. If they turn out to be correct, it would be the first evidence that universes other than ours do exist.

The idea that there are many other universes out there is not new, as scientists have previously suggested that we live in a “multiverse” consisting of an infinite number of universes. The multiverse concept stems from the idea of eternal inflation, in which the inflationary period that our universe went through right after the Big Bang was just one of many inflationary periods that different parts of space were and are still undergoing. When one part of space undergoes one of these dramatic growth spurts, it balloons into its own universe with its own physical properties. As its name suggests, eternal inflation occurs an infinite number of times, creating an infinite number of universes, resulting in the multiverse.

These infinite universes are sometimes called bubble universes even though they are irregular-shaped, not round. The bubble universes can move around and occasionally collide with other bubble universes. As Feeney, et al., explain in their paper, these collisions produce inhomogeneities in the inner-bubble cosmology, which could appear in the CMB. The scientists developed an algorithm to search for bubble collisions in the CMB with specific properties, which led them to find the four circular patterns.

link

[cosmicalstorm]

These things always stun me. Thank you guys for posting these excerpts.