Expert: Courtney Seligman - 8/21/2009

Question
QUESTION: I first heard Carl Sagan discuss a little known theory that the universe might be surrounded by water.  I have heard other astronomers discuss this in a PBS video, where there may be many other universes all sitting as it were, in a giant cosmic sea, like so many expanding bubbles.

I can't find any information about this on your website.  Do you have any info and if so, can you explain it a little more in detail or else, provide some links?


Thank You, Sincerely
Richard Aberdeen
Freedom Tracks Records
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www.FreedomTracks.com

ANSWER: I believe that the discussions you're referring to are a way of visualizing the multiple-universe theory, and are not a description of the theory itself.

(Since the discussion below ended up so long, let me summarize at the start: There is nothing in between the 'bubbles' that represent the infinity of Universes. The 'space' between them is only a way of visualizing the fact that there are a lot of them. It has no existence of any sort -- no space, time, mass, energy, nothing at all -- because it is only a way of visualizing things. In a sense, it's like a graph showing stock market data is not equivalent to the data; it has no physical reality, except as a tool for visualizing things. Now... on to what I hope will be clear, albeit perhaps far too long.)

There is good reason to believe that the Universe was created as a point of zero size in every dimension of reality (however many dimensions of space there are, which is a matter of some debate, and of course the dimension of time). In other words, at the moment of its creation, neither space nor time existed. In the next moment, it expanded to an infinitely larger size, and then began a much slower expansion, which we are still experiencing, and will for the rest of time.

So, if the Universe starts as a point of zero size space-time, how did it come to be? The most popular theory is that in some prior Universe, there were (as in our Universe) vast stretches of empty space-time, in between the vast numbers of galaxies and clusters of galaxies that would have also existed in that Universe. Keep in mind that a point in space-time refers both to a point in space, and in time, so that a single point in space can represent an infinity of points in space-time, as time goes on and on. Now consider how many points of space-time there would be if every point of empty space consists, over time, of an infinity of space-time points. A huge number, obviously. It is the fact that the number of points of empty space-time is unimaginably large that is the basis of the multiple-Universe theory.

The idea is that, in each of these space-time points of essentially zero size, there is no way to know what the actual energy of the points are. They might have more or less energy than zero, according to statistical variations predicted by quantum mechanics. Normally, the amount of energy contained in a point of space-time is essentially zero, but quantum mechanics predicts that there is a very small chance that some space-time points have significant energy.

Keep in mind that if a given point in space has some energy at one moment in time, in the next moment that same point in space, being a completely different point in space-time, might have a completely different energy. And most of the time, even if the point has a large amount of energy at one moment, in the next moment, it will have no energy at all.

So what is the point of all this? Suppose we take the totality of all space-time points, meaning every point in space, at every moment in time, throughout the vast empty spaces of a Universe. Even though most of the points of space-time would have no or very little energy, there is a finite probability that some of them will, for just an instant, happen to have a nearly infinite energy. As long as in the next instant, the energy is undetectable, this not only does not violate any known law of physics, it is actually predicted to be an inevitable result of quantum theory.

Now what happens, if there is a point of space-time which happens to have an unimaginably large energy? According to the multiple-universe theory, when such rare high-energy space-time points occur, they instantly expand to create a new Universe, with a completely separate space-time, which is no way connected to the space-time of the old Universe, save for the one instant when the new Universe came into being. In other words, in the old Universe, you wouldn't be able to tell that anything had happened. In the new Universe, you wouldn't be able to tell that anything happened before it was created, because it was created all at once, out of a single moment of space-time, which has nothing to do with any other point in space-time in either the original or new Universe.

Now, if this idea is true (and most astronomers and physicists believe it must be), then any given Universe is continually creating an infinity of other Universes, none of which have any connection with any other Universe, and they in turn will each create an infinity of other Universes, none of which have any connection with any other Universe. In other words, over time, you have a sort of infinitely expanding foam of Universes, in which each 'bubble' in the foam is a Universe, but there is no connection between any of the bubbles. They are all separated from each other, no matter how big they get.

Now we get back to what you've heard. If we think of an infinity of Universes as bubbles in an infinitely expanding 'sea' of bubbles, what is in between them? The easiest way to visualize this is to compare it to something we're used to, like bubbles in foaming water. That's undoubtedly why you've heard that the Universes are surrounded and separated by water. But that's wrong. They aren't surrounded or separated by anything. As far as any given Universe is concerned, there aren't any other Universes at all. For that Universe, the only space-time that exists is the space-time contained in that Universe. Even the Universes that it spawns are in no way connected to it, as they create their own, completely separate space-time, at the moment of their creation. You might think of them as being very close together at that moment, but since there is no space or time that in any way bridges the gap between them, they might as well be all alone, and the other Universes not exist at all.

So to summarize, although there is presumably an infinity of Universes, which it is convenient and interesting to presume are like bubbles in some gigantic sea, if you want to use that concept, you have to treat the 'space' between the bubbles as not having any existence at all -- it doesn't have any space, time, mass, energy or anything else, because it isn't part of any Universe (if it were, it would be one of the bubbles, not the 'emptiness' between them). But as far as any given Universe is concerned, none of the others (might as well) exist at all.

Finally, since this turned out so long, and it's gotten so late, I haven't taken the time to go back and reread what I wrote, to make sure that it's as clear and uncluttered as possible. I hope that doesn't make it as clear as mud, and want to assure you that if you need me to go over any part of this again, I'll be happy to do so.

---------- FOLLOW-UP ----------

QUESTION: I appreciate your lengthy response, but most of this I am aware of, as it is available on the web.  What puzzles me is that I distinctly recall Carl Sagan talking about a little known theory (at the time) proposed by some scientists that the universe is surrounded by water.  This, according to Sagan, would help explain the abundance of hydrogen in the universe.  Of course, science evidence post-Hubble (i.e., post 1990) is quite different than during Sagan's time, so he might say something quite different if he was alive today.

I've also heard other scientists recently in a PBS video earlier this year discuss the idea of a giant cosmic ocean in which sit many if not an infinite amount of "bubble" universes.  I got the impression from them, unlike the multi-verse theory coming out of the University of Arizona and elsewhere, that they were talking about a liquid water ocean.  Maybe I misunderstood them, but I don't think so and I know my memory is correct regarding what Sagan discussed, because he specifically mentioned the reasoning of the original proposal being that it would help explain the abundance of hydrogen.

ANSWER: I see what you mean. You're referring not to an allegory, but a supposedly actual presence of water in the non-existent space between multiverses. I'm sure that both the theory and its supposed rational are absolutely wrong, and can't imagine why Sagan or anyone else would have ever espoused the idea, because there are several arguments which make it impossible, most of which have been known for the best part of fifty years.

For one thing, the basic idea of multiverses specifically excludes any contact with anything outside any individual Universe. But even if that weren't a problem, there's absolutely no need for water to exist 'outside' the Universe to explain the abundance of hydrogen in it. At the start of the Universe, the mass-energy is in a form unlike anything we can ever experience, but within a fraction of second, as the Universe expands and 'cools', the material becomes the basic building blocks out of which leptons and baryons are formed -- quarks, gluons and such. And as the Universe cools still further, it is inevitable that virtually all of the material not destroyed by matter-antimatter or other annihilations will become the simplest of atomic particles, namely protons (hydrogen nuclei), electrons, and neutrinos (other particles are also formed, but they mostly disappear on time scales too short to be of any importance). Part of the hydrogen is subsequently turned into helium, through the proton-proton cycle of thermonuclear fusion that fuels the Sun, but virtually no other elements are made (as noted below). The fraction of hydrogen that is converted to helium is related to the density of the early Universe, but over a very wide range of densities, going far below and above any reasonable value, the result is about what we observe -- namely, 3/4 of the mass remains as hydrogen, and 1/4 is transformed into helium. So there is absolutely no need to assume that there is some large source of water anywhere, to produce the hydrogen. In fact, it's impossible to not have far more hydrogen than anything else.

Also, if there were a lot of water that could somehow seep into the Universe, then there would also have to be a lot of oxygen (since oxygen atoms are so heavy, almost 90% of the mass of water is oxygen); and although oxygen is currently the third most abundant element, its abundance in the Sun and solar system is more than a hundred times less than it would be if water were in any way responsible for its existence. In addition, in very old stars, the amount of elements other than hydrogen and helium is far less than in younger stars like the Sun, and in stars younger than the Sun, the amount of 'heavy' elements is even greater than in the Sun. As a result, we have absolutely no doubt that even the tiny fraction of oxygen which we now consider normal was not present at the end of the Big Bang, but was all produced by the death of very massive stars. At the end of the Big Bang, there wouldn't have been even the slightest whiff of oxygen, which completely invalidates any theory of water as a source for hydrogen.

---------- FOLLOW-UP ----------

QUESTION: Sorry, in previous response, I should have said, the earth's polarity changes every 200,000 or so years, not the direction of it's spin.  And, the correct number is 250,000 or so, rather than 200,000.  I was curious if modern astronomers agree with this idea which I've seen on the web as well as it was mentioned by Sagan as noted in previous response.

Answer
I've read about theories of displacement of the crust and mantle relative to the liquid core, which would allow the Earth as a whole to maintain a constant rotation (which is essentially a requirement of the law of conservation of angular momentum), while altering the location (though not the direction of rotation) of the various surface features. For Mars, in particular, this theory is being invoked to explain some of the oddities in the polar ice caps; but even there, I'm pretty sure it's a minority view, with most astronomers being totally unconvinced that the concept is either necessary or correct. For the Earth, most discussions I've seen center on the fact that the Moon's tidal forces tend to stabilize our rotation AGAINST such changes, so the idea is even more unlikely.

Not having heard the interview you're referring to, I can only speculate that what he was discussing was changes in the polarity of the Earth's magnetic field, which varies in direction and strength by a small amount from year and year, and completely reverses itself every two hundred thousand to two million years (in the last 70 or so million years; prior to that, reversals were much less common, as far as we can tell). These magnetic field reversals are completely explained by the current theory of the creation of planetary magnetic fields by convective currents in electrically conducting fluid cores (for the Earth, in the molten iron outer core). However, they are not at all regular in their timing, sometimes occurring very close together, and at other times, not occurring for very long periods of time. For a look at the reversals, you might refer to a diagram I posted at the bottom of The Magnetism of the Earth, at http://cseligman.com/text/planets/earthmagnet.htm (unfortunately, there is nothing about this topic on the page except the diagram and a very brief caption, but it graphically illustrates what I just said).