Time Before Time [speculative cosmology]

An event like the Big Bang is about as likely as billions of coin tosses all coming up heads. Explaining why that is might take us from empty space to other universes--and through the mirror of time.

The nature of time is such that the influence of the very beginning of the universe stretches all the way into your kitchen—you can make an omelet out of an egg, but you can't make an egg out of an omelet. Time, unlike space, has an obvious directionality—the view in a mirror makes sense in a way that a movie in reverse never would.

The arrow of time in our universe is puzzling because the fundamental laws of physics themselves are symmetric and don't seem to discriminate between the past and future. Unlike an egg breaking on the side of a frying pan, the journey of the planets around the sun would look basically the same if we filmed them and ran the movie backwards. Rather, it must be due to the initial conditions of the universe—a fact that makes the nature of time a question for cosmology. Remarkably, the answers we're beginning to discover are telling us there may be other universes out there in which the arrow of time actually points in reverse.

For some reason, our early universe was an orderly place; as physicists like to say, it had low entropy. Entropy measures the number of ways that you can rearrange the components of a system such that the overall state wouldn't change considerably. A set of neatly racked billiard balls has a low entropy, since moving one of the balls to another location on the table would change the configuration significantly. Randomly scattered balls are high entropy; we could move a ball or two and nobody would really notice.

Low-entropy configurations naturally evolve into high-entropy ones—as any billiards-break shows—for the simple reason that there are more ways to be high entropy than low entropy. The very beginning of time found our universe in an extremely unnatural and highly organized low-entropy state. It is the process by which it is inevitably relaxing into a more naturally disordered and messy configuration that imprints the unmistakable difference between past and future that we perceive.

Naturally, this leads one to wonder why the Big Bang began in such an unusual state. Attempts to answer this question are wrapped up with the question of time and have led me and my colleague Jennifer Chen to imagine another era before the Big Bang, in which the extremely far past looks essentially the same as the extremely far future. The distinction between past and future doesn't matter on the scale of the entire cosmos, it's just a feature we observe locally.

If time is to be symmetric—if the direction of its flow is not to matter throughout the universe—conditions at early times should be similar to those at late times. This idea has previously inspired cosmologists like Thomas Gold to suggest that the universe will someday recollapse and that the arrow of time would reverse. However, we now know that the universe is actually accelerating and seems unlikely to ever recollapse. Even if it did, there is no reason to think that entropy will spontaneously begin to decrease and re-rack the billiard balls. Stephen Hawking once suggested that it would—and he later called that the biggest blunder of his scientific career.

If we don't want the laws of physics to distinguish arbitrarily between past and future, we can imagine that the universe is really high-entropy in both the far past and the far future. How can a high-entropy past be reconciled with what we know about our observable universe—that it began with unnaturally low entropy? Only by imagining that there is an ultra-large-scale universe beyond our reach, where entropy can always be increasing without limit, and that if we went far enough back into the past, time would actually be running backwards.

Such a scenario isn't as crazy as it sounds. Our universe is expanding and becoming increasingly dilute, and the high-entropy future will be one in which space is essentially empty. But quantum mechanics assures us that empty space is not a quiet, boring place; it's alive and bubbling with quantum fluctuations—ephemeral, virtual particles flitting in and out of existence. According to a theory known as the "inflationary universe scenario," all we need is for a tiny patch of space to be filled with a very high density of dark energy—energy that is inherent in the fabric of space itself. That dark energy will fuel a spontaneous, super-accelerated expansion, stretching the infinitesimal patch to universal proportions.

Empty space, in which omnipresent quantum fields are jiggling back and forth, is a natural, high-entropy state for the universe. Eventually (and we're talking about a really, really big eventually) the fluctuations will conspire in just the right way to fill a tiny patch of space with dark energy, setting off the ultra-fast expansion. To any forms of life arising afterward, such as us, the inflation would look like a giant explosion from which the universe originated, and the quiescent background—the other universes—would be completely unobservable. Such an occurrence would look exactly like the Big Bang and the universe we experience.

The most appealing aspect of this idea, Chen and I have argued, is that over the vast scale of the entire universe, time is actually symmetric and the laws truly don't care about which direction it is moving. In our patch of the cosmos, time just so happens to be moving forward because of its initial low entropy, but there are others where this is not the case. The far past and the far future are filled with these other baby universes, and they would each think that the other had its arrow of time backwards. Time's arrow isn't a basic aspect of the universe as a whole, just a hallmark of the little bit we see. Over a long enough period of time, a baby universe such as ours would have been birthed into existence naturally. Our observable universe and its hundred billion galaxies is just one of those things that happens every once in a while, and its arrow of time is just a quirk of chance due to its beginnings amid a sea of universes.

Such a scenario is obviously speculative, but it fits in well with modern ideas of a multiverse with different regions of possibly distinct physical conditions. Admittedly, it would be hard to gather experimental evidence for or against this idea. But science doesn't only need evidence, it also needs to make sense, to tell a consistent story. We can't turn eggs into omelets, even though the laws of physics seem to be perfectly reversible, and this brute fact demands an explanation. It's intriguing to imagine that the search for an answer would lead us to the literal ends of the universe.

—Sean Carroll is a cosmologist at the University of Chicago and the author of a popular textbook on general relativity. He is also a regular contributor to the physics blog Cosmic Variance.

My point is that it's fallacious to evaluate probability retroactively.

You might think that the odds of this universe coming into existence are a googol-to-one, against. However, the odds of this universe coming into existence are actually one-to-one, a sure thing. We all know this because we're here.

The trick here is that there wasn't much to the universe, neither mass nor size at the start of the BB. Essentially all of the mass and energy came from nothing, no entropy unless there is something, until the inflation phase.

Hi Right Whale! The problem is there isn't much we can definitively say about the singularity prior to the BB. We cannot even say that the physical laws apply to it in any way, for applied retroactively (which reversible time allows), they are all thought to "break down" at that first increment of Planck time. Nor do we know precisely when the inflation began. There are uncertainties or indeterminacies here that may not be soluable.

Guth's remark is very clever. I gather what he's pointing to is the idea that nothing can come from nothing. So there must have been a "something," a first cause, to get the ball rolling (to to speak), but that such a cause may be completely beyond the reach of science.

The BB did not start with nothing. The object was very small, smaller than an atom, and not heavy, 10 kilograms. Nobody is pretending that there actually was such a thing even though the mathematical model with all its attachments reduces to that when it is run back to Start. As you might guess, I believe the BB is an illusion.

As you might guess, I believe the BB is an illusion.

Why would there be an "illusion" before there was any mind to conceive it? I'm sure I'm not following you, Right Whale. Must be my fault.

Do you mean to say the BB is an illusion because the universe is "eternal," i.e., had no beginning?

We can hardly say that the universe is certainly as it appears. If we assume that the red shift is due to speed of expansion of the universe, which is a very recent idea on the cosmological time scale, not even a century old, then we see this. Not much over a century ago meteorites did not come from outer space. Less than a century ago there were no galaxies. Everything was inside the Milky Way. Sometime between 1922 and 1960 the universe acquired galaxies and grew to a billion light years radius with the earth and sun four billion years old, presenting a problem that Einstein indicated needed attention evenwhile he promulgated his Relativity as the explanation of the illusions of EM phenomena. Now the universe has grown to 14 billion light years Hubble radius and is 14 billion years old, but that is not the whole story since the volume of the univeerse outside the Hubble radius and permanently unseeable is ten to the thirty times bigger in volume, but earth and sun remain four billion years old.

Since what we see is still changing every day, what we saw before must have been an illusion, so I merely extrapolate that what we see today is still an illusion.

"Time, unlike space, has an obvious directionality—the view in a mirror makes sense in a way that a movie in reverse never would."

The thing that is obvious is that this poor individual is still abused of the notion that there is such a thing as "directionality" and "location".

I would expand further, but my internal tardis is malfunctioning, and I am therefore unable to bilocate between here and the bathroom at the moment. It's "time" for me to experience all past and future bowel movements in the now. After complete, however, I will return to this thread before it's inception and negate the conversation by correcting the author's misperception, and making thread reversal unnecessary.

I don't really disagree with what you are saying, I just think that measuring time is most likely the answer.

Let's take a unit of measurement like a metre. I seem to remember learning somewhere that there is an official metre stick somewhere in France. I know that the metre is based on some scientific unit based on the wavelength of light(?). If you aligned the metre lengthwise along an axis that was subjected to a great force (say a gravitational well) that literally pulled the atoms in it closer together, it would be shorter, but maybe the wavelength of light aligned in parallel would be as well. Does this make it not a matre anymore?

I don't know the answer, but I feel the same way about time.

Something I've always wondered: If a universe spontaneously forms & inflates inside a parent universe, what would happen to anything or anyone who's already inside the parent universe, say within 100 million light years away? Seems to me that would be quite destructive, as in pretty much completely destroying the whole parent universe.

The other scenario, I guess, would be that the new universe could always look like a tiny patch of space inside the parent universe. The baby universe simply gets more & more complex, even as it looks from the inside like it's expanding rapidly in size. This way the new universe wouldn't harm anything in the parent universe - but that strikes me as totally ad-hoc.

Since what we see is still changing every day, what we saw before must have been an illusion, so I merely extrapolate that what we see today is still an illusion.

Ergo, it's all an illusion -- the universe and all its contents, within or outside the Hubble radius? (Not that we could have anything at all to say about the latter.)

Are you saying that when a thing changes, whatever its prior form was, it is now an illusion? But things are changing all the time. Does that mean the universe itself is an illusion? And does that mean that you and I are illusions too?

You are not separated in Time.

You are separated by angular distance indicative of your positions on the earth's surface relative to the sun. Because the rotation period of the earth is defined as 24 hours, your angular position can be defined as a fraction of that rotation period -- IOW, some fraction of 24 hours.

Nonetheless, you both looked at your watches at the same instant in Time.

"The low-entropy beginning of our cosmos does appear to be very highly improbable...which is not to say it can't happen."

Entropy and Order appear to be subjective terms used to mean anything the cosmologist needs it to mean to prove their point. The period after the big bang, whether it be pre- or post-inflationary period was chaotic with huge superhot clumpy clouds of gas and plasma that had no order whatsoever. Once the matter coalesced into into galaxies, stars, and planets then order finally began to appear, and entropy was reduced. Increasing entropy may rule the universe today, but I don't think that was always the case.

As an Eleatic Thomist I might be inclined to try that solution first unless there is somethng else crying out for preference.

I tend to think, along with Aquinas, that Avicenna was misled when he said that Aristotle said the universe must have existed eternally. The correct eleiatic position, and the correct philosophical position altogether would be that it cannot be proven that the universe either began at some time or that it has eternal existence in that direction even though it may have eternal existence from now on--can't say anything about that, either. As far as the Theologians go, the Text does not support either an eternal universe or a creation from nothing although it can be misread and commonly is in many of the translations we have available.

As to the illusion of the BB: a serious problem exists that Guth solved by his inflation. But, to a layman inflation is no better than simply turning the universe inside out; it is in effect turning the universe inside out. The problem is that the farther we see back in time, if we read the data correctly we are seeing to a time when the universe was smaller than an atom. However, and this is the problem, the farther we see the bigger it gets. These are not two compatible ideas. So this is why inflation was proposed and inflation brings a potload of other strangeness with it. Might as well say the universe inverted or mapped itself to an inverse function. That plays havoc with isotropy, which even Relativity has to assume in order to have a starting point.

It depends on the nature of space, I guess. What happens to the parent universe while there's this enormous spatial expansion going on within it? I can imagine two possibilities:

1. The space of the parent is swept outward, pushed by the inflating space within it. That seems to require some kind of "substance" to space -- at least for this purpose -- which I don't understand, but I guess it's possible. The parent universe would end up surrounding the new universe. The most distant stars (if they existed in the parent) would appear far too old. This hasn't been observed.
2. The inflating space simply "blows by" the existing parent universe and goes on expanding. The result is that the new universe ends up surrounding the parent. The parent region might be observable as a discrete portion of the visible universe, and (if it had stars) it would have older stars than we might otherwise expect -- but only if it were at the horizon of the visible universe, which it probably wouldn't be. If the parent universe were made of dark matter, it wouldn't be observed anyway.

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TIME BEFORE TIME