I agree in my desires.

What if it is easier to go to a parallel universe than to travel to the stars? It could explain where all of the aliens are ( Fermi Paradox).

Has anyone considered the possibility that dark matter is the gravitational influence of parallel universes?

To this non-physicst, this parallel universe fantasy founders on the concept of "event." Precisely what is an event? Precisely when does it begin? This is an analog universe and there is no discrete moment definable as an event.
It's like saying that a parallel universe splits off at every moment. Precisely what is a moment? Time is not discrete. There may be limits to its measurement, but it has no known temporal granularity.
Can physicists really be oblivious of such an obvious fact?

As a science fiction idea, I think it would be fun if the parallel universes that experience time at different rates relative to each other combined with the ability to jump between them. That way there would be a parallel universe split off from the Roman Empire days, that one can go visit etc etc. So time travel without the silly paradoxes, you just create more new universes. You may not be able to get back to your exact universe, but maybe one very similar to it.

But can we ever get to them?

Traversable wormholes?

"This is an analog universe and there is no discrete moment definable as an event."

My interpretation...

Reality is discrete. Much as pixels make up a digital image, there are discrete 4 dimensional (3 space and 1 time) volume-time "bricks" that are indivisible units of the universe. As matter and energy are also discrete, a finite volume of space-time has a finite number of possible states. (Just as an idealized digital computer has a very large, but finite number of possible states.) This implies that all measurable values are ultimately discrete and the transitions between discrete states are discontinuous. Since the space-time unit is so small, continuous function approximations give good results.

Unlike the regular rectangular pixels of a digital image, the 4-D "bricks" have a complex geometry that reflects General Relativity. There is also evidence that there aren't really 3 spatial dimensions. Instead space is fractal. Imagine reality as a digital two-dimensional surface that we observe as a 3-D holographic projection of that surface. (Hologram theory associated with LIGO measurements.) The fractal nature becomes apparent at extremely small scales. ("Information conservation" as electromagnetic radiation is captured by a black hole.)

Also note that contrary to our macroscopic intuition, objects don't have unique identities. "Individual" electrons don't exist. Instead there are just wave form peak amplitudes that we track and interpret as specific electrons.

Finally, note that Schrodinger Equations are a continuous deterministic system that appears to closely approximate reality as measured by experiment. At the Schrodinger level there are only wave functions. There are no observations that collapse probabilities into "real" events. There are no multiple universes...just one continuous universe with waveforms that linearly sum. The Born Rule provides a way to map the waveforms to predictions of experimental outcomes.

Now consider classical physics and clouds of gas coalescing to form galaxies. Under the force of gravity, small differences in gas density leads to density clusters that eventually forms stars and galaxies. Stars emit radiation that accelerate gas away from the star, creating gas density waves (especially when a massive star goes super nova). The result is high density galaxies in an expanding universe. Within the galaxies matter and energy strongly interact, but individual galaxies are moving apart and are almost totally independent (with the occasional rare "collision" of nearby galaxies). In a similar manner, in the Schrodinger Equation universe, waveforms interact, clustering at some levels and dispersing at different levels...creating high density "reality peaks" in a vast space consisting primarily of low density waveforms. Much as neighboring galaxies might occasionally collide, nearby "reality peaks" might occasionally interact.

A new theory is needed that modifies the Schrodinger Equation and General Relativity to account for the discrete, fractal nature of energy-space-time. The theory should explain how waveform interactions lead to clustering and dispersion, producing the experimental observations that some scientists interpret as Born probability wave collapse and others interpret as Many Worlds splitting.

I demand proof. Show me the universe where Hitler grew up to be a Carmelite nun, and maybe I'll buy this multi-universe crap.

I demand proof. Show me the universe where Hitler grew up to be a Carmelite nun, and maybe I'll buy this multi-universe crap.
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Show me "the" universe? Obviously there are an infinate number where that has happened, is happening and will happen. So elementary.

Randall, why do you want to travel between universes? How do you know before hand that the universe you travel to would be anthropically acceptable for you to at least survive in?

> HOW many universes are there?

How many angels can dance on a pin head?

I'm always amazed at the ability of people to pass groundless theorizing as science.

Before paying any attention to the numbers of universes (said numbers being tossed around by the Highly Trained Scientists(tm)), I'd like to hear about an empirical proof that there's at least one other Universe.

Speaking as someone with a BA in Sociology--but who has read Brian Greene's The Fabric of the Cosmos: Space, Time, and the Texture of Reality, which I'd recommend to anyone who'd like a mostly nonmathematical explanation of all this stuff, that'd be a good start.

Some points:

Q. Are there actually multiple universes, or is that just science fiction?
A. Probably no one will ever know for sure. The mathematics of string theory strongly suggest it, but it's also possible that string theory will never be proven--or disproven, because it would involve looking at Planck-scale thingies (like strings), and that would take an atom smasher the size of the Moon. We may get some corroboration from observational astronomy--and so far that's been pretty good. But it's not proof in the way that actual experimental proof would be. This isn't a fault of string theory. We're just bumping up against the edge of what build-able instruments (like the Large Hadron Collider, if it ever works) can show us in terms of how small a scale they can reveal.

However, multiple universes would explain why this universe is so darn friendly to life. It runs on a number of forces whose exact strengths produce a set of Laws of Physics that makes stars, galaxies, planets, and life possible. If any of their strengths differed this wouldn't be true and our universe would be a lightless plasma or some such.

But if there are a bazillion universes out there with arbitrarily varying constants, it's perfectly reasonable to have one like this.

Religious scientists believe the life-supporting character of our universe offers objecting proof of a benevolent deity BTW.

One more thing--each universe, if there are multiple ones, exists on a multidimensional something called a brane, with all the universes/branes existing in some metauniversal space-thingie called the bulk. One possibility, also suggested by string theory, is that the Big Bang was caused by two branes touching, which pushed the big Reset Button in the sky. Theoretical noodlings suggest that this would only happen once in a very, very, very great while, so no need to hide under the coffee table. But if it did happen all the information in this universe would be erased--including us.

Q. So are universes splitting off at every point in time?
A. I don't think that's what string theory posits. More like all at once. Certainly not at decision points, which then means time doesn't need to be divided into quantalike bits.

Q. Wormhole travel?
A. Your mass would remain, but nothing else--in physics terms, information--would be retained. Imagine being pureed at in a lightspeed blender.

Q. Travel between parallel universes?
A. String theory suggests that the only thing not limited to our brane is gravity, which would account for it seeming to be so much weaker than other fundamental forces. If that's true it's just as strong as the other forces but diffused across universes. Other than that, I don't think interuniverse travel is possible, though I'm working on a sci fi novel where it is. But that's what makes it sci fi I suppose. I'm making up for this by not going against what we know about reality in any other way BTW.

Hope this helps. I'm just going off memory of Greene's book that I read several years ago. Consult his book for the real deal.

It's now fairly well accepted that because the curvature of space within our Hubble space (visible universe) is near unity, implying that this space is flat and therefore has no logical EDGE or end, (SPACE STOPS HERE). And, unless we live in a most unique spot in space (the center of the known universe- sound familiar) Hubble volumes centered at the edge of ours will result in the same flat universe, and so on. Might there be a limit where the shape of space finally varies from unity? Surely. But Tegmark, and others have shown that to not raise the SPACE STOPS HERE flag the minimum size of our universe is vastly larger than our own Hubble space.

Now only so much stuff can be packed into any given space, and by our known laws of physics certain packaging is not permitted. By Tegmark's calculation the number of possible slots to fill in our Hubble volume is 10^10^115 at temperatures below 10^8K. So, there is almost certainty that potions of our Hubble volume are repeated in other Hubble volumes, possibility in our own. And if space is large enough entire Hubble volumes and multiple adjacent volumes must also be repeated. So, again as Tegmark points out, multiple universes, actually Hubble volumes, are the most logical and real, unless someone can prove a non-unity shape for space.

As to other types of multiple universes, what makes "our" big bang unique. Again, are we the center of everything?

Now this is the part I like. Scientists are finally beginning to grasp the concept of the difference between distance and space (the void, the bulk). The acceptance by most scientists of the inflationary model for our big bang has in no small way led to this revelation. Thus the distance we measure between Earth and Alpha Centuri is expressed in light years. As far as I know the space between these two has no known units. Light appears to put a limit on how fast we can span the distance between destinations. Yet inflation has shown that space has expanded much faster resulting in two destinations being much farther apart than light can travel over an equal time. There has been debate offering the conjecture that if space can expand it also can contract. At this moment methods to do this have been speculated, and all require the use of massive amounts of exotic matter and energy. In human exploration and science it is our history to start with the difficult and extreme and over time simplify. Maybe this is the case here. A few years ago this thought was still unknown. So here comes the what ifs. If we can learn to manipulate space-time we don't need to travel to Alpha Centuri, anywhere else in our "home" universe, or for that matter in those other level multiple universes. Why, because space-time is independent of what is within any given space-time. We don't travel to a galaxy far far away we contract, or eliminate, the space-time between us and the distant galaxy. Sure, there are all types of potential criticisms, like what happens to all the stuff between the two destinations? I believe, the science argues that the space between objects is independent of the stuff within that space. For example, if Mars is in between Earth and Alpha Centuri, then contracting space may be a problem. But, wait x time and Mars is somewhere else. Thus space-time again is independent of the stuff occupying any relative single space-time. Our "trip" to Alpha Centuri, a galaxy far far away or even to another universe might well be instantaneous.