Death from the Skies! (41 page)

You might consider that a drawback.

But the alternative is the boring Universe where nothing ever happens. So let’s see what we’ve got.

The Big Bang was a singular happening. Somehow, all matter, energy, space, and time were generated in that one event, forming the Universe as we know it.

But where did that event come from?

As discussed earlier, there are some theories that there is a meta-Universe, someplace
other
that exists outside of our framework of space and time. It developed a little quantum hernia, and this formed our own Universe. If that’s really the case, then the death of our Universe isn’t that big a deal in context. The other Universe may still be there, and it’s possible that it budded off countless other universes too. These may all have vastly different laws of physics (maybe in one the speed of light is a few miles per hour instead of 186,000 miles per second, and in another the electron has more mass than the proton, instead of the other way around as in ours). It’s also possible that our own Universe is doing this all the time—even now, tiny offspring universes are popping into existence in other “places,” outside what we can see and investigate. However, according to everything we understand about physics, we can never physically learn anything about these other universes, so for all practical purposes they don’t exist.

Of course, it’s conceivable that in the next, oh, quintillion years or so our understanding of physics may change. I’ll readily grant that! But for now there’s not much we can say about this.

But maybe we’re starting off on the wrong premise. Maybe we should ask:
was
the Big Bang actually the first cause? Or was there some other event that jump-started the cosmos?

There is another idea, still in its infancy, called the
ekpyrotic universe
(Greek for “from [or out of] fire”). According to this idea, the Universe is already incredibly old. At first, it was basically a giant void, with nothing interesting happening (much like the way we left it after 10
¹⁰⁰
years). According to this theory, there exist other universes with characteristics similar to those of ours now, but these other universes are outside our view. They exist in eleven dimensions instead of the four with which we are familiar (the three dimensions of space and one of time), and they float around in this extradimensional space. Called
branes,
short for
membranes,
these are all self-contained universes like ours in many ways, generally minding their own business.

But sometimes they collide.

You can picture these universes as parallel plates floating around. When they smack into each other, they shake up the contents rather vigorously. The theory predicts that the universes would get violently disturbed, with energy and matter being heated up tremendously, and space itself set to expand.

Sound familiar?

This may sound a little like fantasy, but it’s all part of a set of very complicated but scientifically based math and physics theories. No one has any idea if these theories really are viable alternatives to the Big Bang model, or if it’s just so much fantasy. But the ideas are internally consistent, and are being studied very seriously.

If they pan out, then there is some hope for the Universe, or at least for some meta-Universe: it means other universes exist, and they might be habitable. We can never reach them, so that’s too bad for us, but maybe other species in those universes can survive.

And there is some hope for us as well. What happens once can happen again, especially if you wait long enough.

In 10
¹⁰⁰
or 10
^1,000
years, however long it takes, another brane may collide with ours. When it does, it may spark a reignition of the Big Bang, kick-starting our Universe once again. When that happens, pretty much everything that happened in the Universe before that point will be destroyed: kindling, if you will, for the fires of a new Universe. Again, that’s too bad for us, but it does mean that there is a cyclical nature to reality, and a chance for life to rise anew.

Again, cold comfort. But it’s a possibility.

Yet another fate may wait in store for us in this far distant future, and we have even less of an idea of what will exist after it unfolds.

Objects have what is called an
energy state.
It’s a bit like climbing a set of stairs. On the bottom step you are at the lowest energy state, and at the top you’re at the highest. There are energy states in between too. It takes (muscle) energy to move up to higher states, and you give up that energy when you go back down.
¹³⁴
Sitting at the bottom, you’re as low as you can go, and you stop.

Atoms behave this way: electrons zipping around an atomic nucleus have certain energy states available to them, with none in between (just as you can’t stand on the four-and-a-halfth step; it doesn’t exist, so you have to be on either the fourth or the fifth step). This is one of the most basic ideas of quantum mechanics.

Perhaps the Universe behaves this way as well. We think of the vacuum of space as being, well, a
vacuum.
Empty. Devoid of matter and energy, and therefore at its lowest energy state.

But this may not be the case: we know that space bubbles and boils with energy at extremely small size scales (this is the basis for Hawking radiation, in fact). So what if we’re not at the lowest energy level, the lowest energy state? What we’re experiencing now would then be a “false vacuum state,” and we might take that final step down, dropping to a lower state.

The starting point for this drop is difficult to predict. Maybe it’s a quantum effect, again like Hawking radiation: somewhere, someplace in the Universe, a teeny-tiny bit of the Universe suddenly drops to the lower state. According to the theory, this one event acts as a trigger, pushing regions around it to drop into the lower state as well (imagine standing on the second-to-last step from the bottom with ten other people; you jump down and drag everyone else with you). A cascade starts, with more and more bits of the Universe dropping to the lower state.

This tunneling event, as it’s called, would expand outward in a sphere at very nearly if not at the speed of light. It’s a bit like a sugar crystal growing in a supersaturated solution; once you start it someplace, the other sugar molecules attach themselves there, growing rock candy.

In this case, though, the rock candy is the collapse to the true vacuum, and the sugar molecules are actually the fabric of space itself. The damage wrought is literally total.

Inside this expanding bubble of vacuum collapse,
the laws of the Universe change.
Space and time themselves are rewoven, becoming something entirely new, something the nature of which we cannot even begin to guess. Anything caught in this wave will be utterly destroyed.

And there is literally nothing to stop it. The entire Universe sits on the second-to-lowest state, so once poked by the expanding bubble,
everything
will collapse. Every star, every planet, every black hole, every human.

That would be pretty bad, were it to happen today. Odds are it won’t; the chances of this happening are extremely small. But if this event were to wait, say, 10
²⁰⁰
years, would that be so bad? I argue it would be
good.
By that time the Universe will be dead, stagnant, with nothing to show for all those years of activity. A collapse of the false vacuum to the true vacuum would possibly reenergize the Universe, giving it a second chance for life.

So there is some hope. You and I and even the entire Universe as we know it won’t be there to witness it, much less survive it.

But afterward, a new Universe will be created, sparkling and clean and ready for a new start. In this case—and also that of the ekpyrotic universe, and maybe even other processes we haven’t even yet conceived of—there is a chance that instead of a bleak and dim future, filled with nothingness for all eternity, there will be a rebirth of the Universe, and the rebirth of possibilities.

And if it happens once, it might happen again in another 10
²⁰⁰
years, or 10
^1,000
. And again, and
again.
Endlessly.

Rather than dealing out death and mayhem, destruction and chaos, the Universe will cyclically clean itself out, reboot, and set everything in motion once again.

Each time, perhaps, the laws will be different, and the characteristics of that future infinite parade of universes will be grandly set apart from what we know today. And despite our prejudices, the Universe appears to have no set of rules on how things need to be for complex chemistry, for life, to arise.

We don’t know for sure if there are aliens in our own Universe now, though the odds favor such a possibility: there are 200 billion stars in the galaxy, and hundreds of billions of galaxies in the Universe.

And so I wonder: can we now multiply those odds by the number of potential universes that lie ahead as well?

If that’s the case, then the Universe provides us a near-infinite number of do-overs, something I find very uplifting. It may seem that the Universe spends all its time trying to kill us, but in the end—the
very
end—there may yet be Life from the Skies.

Good. It’s been quite a ride, but I hope that while you read this book you weren’t vaporized, crushed, irradiated, flung out into deep space, spaghettified, or had any of your protons decay.

We’ve covered a lot of scary ground (not to mention space and time). It seems as if the whole cosmos is trying to snuff us out. In a sense, it is—there’s danger aplenty in the Universe—but we have to take a practical view here. We have to appreciate the vastness of space and time, and our ability to manipulate events around us.

Asteroid impacts provide an excellent example of practical versus theoretical danger. They have done ferocious damage to the Earth in the past, and our relatively fragile economic system could be destroyed by far smaller impacts than the one that did in the dinosaurs. To understand the actual danger, we have to balance the idea that they don’t happen very often with the knowledge that they do in fact
sometimes
happen.

In your daily life, this may not present much of a problem (except for when you lie awake at night and your brain, unfettered by the common sense available during the day, is wondering if tonight is
the night
). But in the case of impacts, we can actually prevent them from happening. It would cost a lot of money (hundreds of millions to test various ideas, and hundreds of millions more to implement them), time, and effort. Can we afford to start worrying about this now? Can we afford to wait?

Scientists are asking these questions, because they have to ask Congress for a lot of money to be able to do anything about them. And what Congress decides influences your money (other governments may become involved as well). To make sure we get the right answers, we really have to understand the issues. Astronomers are looking at a theoretical danger and finding a practical action to take against it.

I hope this book has cleared some of that up. I studied gamma-ray bursts for many years, and I personally am not at all worried about them. Nor do I fret over the death of the Sun, the eventual decay of the Universe, or a black hole slipping through the solar system and snacking on the odd planet or two. That’s because I understand the odds of these events actually taking place, and they are vanishingly small. There’s no need to worry about them, whereas an asteroid strike or a particularly nasty solar coronal mass ejection can do a lot of damage. Even then we have it within our power to minimize their impact.

In an effort to make all this a little easier to digest, here is a table that gives the odds, the potential damage, and our ability to prevent the disasters described in this book. What you’ll see is that chapters 1 and 2—asteroid impacts and solar events—cover the only two events we can do anything about. While they may not happen tomorrow, they will happen, and it’s in our best long-run interest to do something about them.

Following the table is a description of how I came to those conclusions. Bear in mind that astronomy is a field of science, and that means that things change as better data and better ideas come along. Don’t assume any of this is written in stone.

Of course, in 10
⁴⁰
years or so, even stone will be long gone.