1. We are living in a computer simulation.
The Theory: The Matrix is real, and we are living in it.
How Likely Is It? Difficult to say – at the moment. Though this sounds incredibly far-fetched, at some point we might be able to test for it. The computer simulation could leave behind a signature from it’s underlying structure that we could detect through cosmic rays. Scientists couldn’t prove we are in a simulation, but could find evidence that suggests we are.
2. A 4D black hole collapsed to form the universe.
The Theory: Some physicists think that the universe might have started with the collapse of a 4D black hole, and that the ejected debris formed the universe we live in.
How Likely Is It? We can never truly know what happened before our universe began, so it’s certainly possible. And it does address some currently unanswered questions. But it’s still early days for this theory, and more research is needed to say one way or another.
3. The multiverse.
The Theory: Our universe is just one of many parallel universes, or maybe even an infinite number of parallel universes, in existence.
How Likely Is It? There are plenty of compelling arguments for the existence of the multiverse. And some physicists claim that recent data from the Planck satellite provides evidence for it.
4. The big crunch.
The Theory: The universe will end in a “big crunch” as galaxies are pulled back together by gravity, ending in a kind of reversed Big Bang.
How Likely Is It? This theory requires gravity to overpower the force pushing the universe apart. That doesn’t look likely to happen, so we should escape this scenario.
5. The big rip.
The Theory: The universe will expand so much that eventually galaxies, solar systems, planets and even individual atoms will be ripped apart.
How Likely Is It? Probably not going to happen. Though the latest results from the Planck satellite do push it slightly more into the realm of possibility than it was before.
6. The big freeze.
The Theory: This is what will happen if the universe keeps expanding forever, but not enough to rip itself apart. The stars will go out and the black holes will evaporate. Also known as the “heat death” of the universe, it’s the sweet spot between a big crunch and a big rip.
How Likely Is It? All evidence points to a this as the fate of the cosmos. The end of the universe is going to be a cold and lonely place. But at least the atoms won’t be ripped apart.
7. Our universe is a hologram.
Theory: The universe is a giant hologram, or, in more scientific language, “a projection of a two-dimensional shell”.
How Likely Is It? Hard to say. If this theory is right, the universe should be “grainy” once we get down to a certain level, like pixels on a computer screen. What looked like evidence for those pixels has now been superseded, and it seems that, if they do exist, they are too small for us to probe. So we might never know if we’re living in a hologram or not.
8. The universe is lopsided.
The Theory: Scientists have long thought the universe looked the same in all directions, but this theory says that’s not the case – some bits of space are hotter than others.
How Likely Is It? Lots of evidence points to this being true. The latest comes from the Planck satellite that took a snapshot of the cosmos further back in time than ever before. More difficult is trying to work out why this is the case.
9. Dark energy is pushing the universe apart.
The Theory: Everything in the universe is being pushed apart by an invisible force called dark energy. It’s so powerful that it’s making the expansion of the universe accelerate.
How Likely Is It? Very. The 2011 Nobel Prize in Physics was won by two teams who discovered the accelerated expansion of the universe. Dark energy is not necessarily what is causing this, but many physicists do think it is the culprit.
10. Time is slowing down.
The Theory: Distant stars only look like they’re rushing away from us. But rather than stars speeding up, it happening because time is slowing down and we’re looking at them in the past, when time passed quicker.
How Likely Is It? Not very, but it’s not completely out of the question. This theory solves the same problem dark energy does, and most physicists are still firmly in the dark energy camp.
11. Black holes are portals to other universes.
The Theory: Black holes are wormholes that connect our universe to other universes. Wormholes are hypothetical warps in the fabric of space-time that form a sort of tunnel.
How Likely Is It? Possible. Wormholes are still firmly in the theoretical realm, so it’s impossible to say either way at the moment if the theory is true. But the mathematics behind it does solve the problem of losing information that falls into a black hole, as a wormhole would ensure it’s never really lost.