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The second multiverse theory arises from our best ideas about how our own Universe began. According to the predominant view of the Big Bang, the Universe began as an infinitesimally tiny point and then expanded incredibly fast in a super-heated fireball. A fraction of a second after this expansion began, it may have fleetingly accelerated at a truly enormous rate, far faster than the speed of light.
This burst is called "inflation". Inflationary theory explains why the Universe is relatively uniform everywhere we look. Inflation blew up the fireball to a cosmic scale before it had a chance to get too clumpy. However, that primordial state would have been ruffled by tiny chance variations, which also got blown up by inflation.
These fluctuations are now preserved in the cosmic microwave background radiation, the faint afterglow of the Big Bang.
The Unreality of Time
This radiation pervades the Universe, but it is not perfectly uniform. Several satellite-based telescopes have mapped out these variations in fine detail, and compared them to those predicted by inflationary theory. The match is almost unbelievably good, suggesting that inflation really did happen. View image of Just after the Big Bang Credit: This suggests that we can understand how the Big Bang happened — in which case we can reasonably ask if it happened more than once.
The current view is that the Big Bang happened when a patch of ordinary space, containing no matter but filled with energy, appeared within a different kind of space called the "false vacuum". It then grew like an expanding bubble. But according to this theory, the false vacuum should also experience a kind of inflation, causing it to expand at fantastic speed. Meanwhile, other bubble universes of "true vacuum" can appear within it — and not just, like our Universe, This scenario is called "eternal inflation".
It suggests there are many, perhaps infinitely many, universes appearing and growing all the time. But we can never reach them, even if we travel at the speed of light forever, because they are receding too fast for us ever to catch up. After Copernicus suggested Earth was just one planet among others, we realized that our Sun is just one star in our galaxy, and that other stars might have planets. Then we discovered that our galaxy is just one among countless more in an expanding Universe. And now perhaps our Universe is simply one of a crowd. View image of Credit: However, if eternal inflation does create a multiverse from an endless series of Big Bangs, it could help to resolve one of the biggest problems in modern physics.
The fundamental constants of the laws of physics seem bizarrely fine-tuned to the values needed for life to exist. Some physicists have long been searching for a " theory of everything ": But they have found there are more alternatives to choose from than there are fundamental particles in the known universe. Many physicists who delve into these waters believe that an idea called string theory is the best candidate for a "final theory".
But the latest version offers a huge number of distinct solutions: Each solution yields its own set of physical laws, and we have no obvious reason to prefer one over any other. The inflationary multiverse relieves us of the need to choose at all. If parallel universes have been popping up in an inflating false vacuum for billions of years, each could have different physical laws, determined by one of these many solutions to string theory.
View image of Bubble universes Credit: Things have to be the way we find them: For example, if the strength of the electromagnetic force were just a little different, atoms would not be stable. Similarly, there is a delicate balance between gravity, which pulls matter towards itself, and so-called dark energy, which does the opposite and makes the Universe expand ever faster.
This is just what is needed to make stars possible while not collapsing the Universe on itself. In this and several other ways, the Universe seems fine-tuned to host us.
This has made some people suspect the hand of God. Yet an inflationary multiverse, in which all conceivable physical laws operate somewhere, offers an alternative explanation. View image of Other universes might be different to ours Credit: In every universe set up in this life-friendly way, the argument goes, intelligent beings will be scratching their heads trying to understand their luck. In the far more numerous universes that are set up differently, there is no one to ask the question.
The Unreality of Time
This is an example of the "anthropic principle", which says that things have to be the way we find them: For many physicists and philosophers, this argument is a cheat: How can we test these assertions, they ask? Surely it is defeatist to accept that there is no reason why the laws of nature are what they are, and simply say that in other universes they are different?
The trouble is, unless you have some other explanation for fine-tuning, someone will assert that God must have set things up this way. The astrophysicist Bernard Carr has put it bluntly: View image of Two branes collide, creating a new universe Credit: Another kind of multiverse avoids what some see as the slipperiness of this reasoning, offering a solution to the fine-tuning problem without invoking the anthropic principle. In he proposed that universes might reproduce and evolve rather like living things do.
On Earth, natural selection favours the emergence of "useful" traits such as fast running or opposable thumbs. In the multiverse, Smolin argues, there might be some pressure that favours universes like ours. He calls this "cosmological natural selection". Smolin's idea is that a "mother" universe can give birth to "baby" universes, which form inside it. The mother universe can do this if it contains black holes. View image of A black hole Credit: A black hole forms when a huge star collapses under the pull of its own gravity, crushing all the atoms together until they reach infinite density.
This suggested to Smolin that a black hole could become a Big Bang, spawning an entire new universe within itself. If that is so, then the new universe might have slightly different physical properties from the one that made the black hole. This is like the random genetic mutations that mean baby organisms are different from their parents. If a baby universe has physical laws that permit the formation of atoms, stars and life, it will also inevitably contain black holes. That will mean it can have more baby universes of its own. Over time, universes like this will become more common than those without black holes, which cannot reproduce.
View image of Could one universe create others? It is a neat idea, because our Universe then does not have to be the product of pure chance.
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If a fine-tuned universe arose at random, surrounded by many other universes that were not fine-tuned, cosmic natural selection would mean that fine-tuned universes subsequently became the norm. The details of the idea are a little woolly, but Smolin points out that it has one big advantage: For example, if Smolin is right we should expect our Universe to be especially suited to making black holes. This is a rather more demanding criterion than simply saying it should support the existence of atoms.
But so far, there is no evidence that this is the case — let alone proof that a black hole really can spawn an entirely new universe. View image of Extra dimensions could be curled up Credit: You would die, but that'd be the least of it. The atoms in your body would simply cease to be. Instead of ashes to ashes, you'd have ashes to The new emergent space-time theories suggest a different picture in which space undergoes a change of state in a black hole. The black hole does not have an interior volume; its perimeter marks where space melts. The result is a new state that is no longer spatial and is scarcely even imaginable in human terms.
If you fell in, you would probably still die, but the atoms in your body would still carry on in some new form. Consider, also, the big bang. Like black holes, it has always posed something of a paradox. The ordinary laws of physics, operating within time, are inherently unable to explain the beginning of time. According to those laws, something must precede the big bang to set it into motion.
Yet nothing is supposed to precede it. A way out of the paradox is to think of the big bang not as the beginning but as a transition, when space crystallized from a primeval state of spacelessness. Finally, consider the mysterious phenomena of quantum nonlocality -- what Einstein called "spooky action at a distance.
The particles behave as though they are not, in fact, separated. And one possible explanation is that the particles are rooted in the deeper level of reality where distance has no meaning. To be sure, this is all still speculation -- but it is constrained speculation.
Scientists didn't dream up these ideas over drinks after work. They were driven to them by combining the principles of Einstein's theory and of quantum theory and seeing where the path takes them. By the very nature of research, we don't know what these ideas mean or even if they're right.
Why Space and Time Might Be an Illusion
But we do know that humans have not yet grasped all there is to grasp about the universe. And when we do take the next step, the effects will surely propagate into our broader culture. This is simply the weirdness that special relativity entails. Consequently, many philosophers have used special relativity as evidence against a theory supporting the A series of time.
In an attempt to reconcile these two theories, some well-known physicists have developed theories of quantum gravity that imply the world lacks time in a fundamental way. Monton cautioned, however, that quantum gravity does not imply the same lack of time that McTaggart may have had in mind. Physicist John Wheeler, as Monton notes, has postulated that time may not be a fundamental aspect of reality, but this only happens on extremely small distance scales. Some of these ideas in quantum gravity may be radical, but several respected names in physics are seriously considering a reality without time at its core.
If a quantum gravity theory emerges that requires a radical conception of time, McTaggart may help us prepare. As Monton writes in his paper: Laser blasts and levitation team up to make testing water for heavy metals a cinch! When GPS isn't an option, scientists turned to physics to control and track swarms of underwater sensors. Sometimes, all it takes to unlock ancient secrets is to look at the problem in a new light. American Physical Society Sites: The Unreality of Time Image Credit: Two Times, One Contradiction With this distinction in place, McTaggart additionally argues that a fundamental series of time requires a change to take place.
Analyzing Water with Lasers and Levitation Laser blasts and levitation team up to make testing water for heavy metals a cinch!