Why is the universe the way it is? Scientists have explored many ways to explain the cosmos, leading to some crazy-sounding ideas.
By How It Works magazine, Andrew May
(Image credit: Shutterstock)
Why is the universe the way it is? Over the years, scientists have explored many ideas to explain our cosmos and its future. Here are some of the strangest ideas, from a braneworld scenario that involves the universe floating in a higher dimensional space, to the "Big Splat" that describes such a brane colliding with another to form an entirely new universe.
1. Braneworld
(Image credit: Shutterstock)
An aspect of the universe we take for granted is that it's three dimensional — there are three perpendicular directions you can move in. Some theories, however, suggest another spatial dimension — which we can't perceive directly — in another perpendicular direction. This higher dimensional space is referred to as "the bulk," while our universe is a three-dimensional membrane — or "brane" — floating inside the bulk.
As complicated as it sounds, the braneworld picture solves several problems in physics. For example, theoretical physicists Lisa Randall, of Harvard University, and Raman Sundrum, of the University of Maryland, proposed a version of the braneworld that explains an asymmetry in subatomic forces by suggesting the existence of other branes parallel to our own. But it's not enough for a theory to explain facts we already know — it has to make new predictions that can be tested experimentally. In the case of the Randall-Sundrum model, such tests could involve measuring gravitational waves emitted by black holes linking one brane to another.
Why is the universe the way it is? Over the years, scientists have explored many ideas to explain our cosmos and its future. Here are some of the strangest ideas, from a braneworld scenario that involves the universe floating in a higher dimensional space, to the "Big Splat" that describes such a brane colliding with another to form an entirely new universe.
1. Braneworld
(Image credit: Shutterstock)
An aspect of the universe we take for granted is that it's three dimensional — there are three perpendicular directions you can move in. Some theories, however, suggest another spatial dimension — which we can't perceive directly — in another perpendicular direction. This higher dimensional space is referred to as "the bulk," while our universe is a three-dimensional membrane — or "brane" — floating inside the bulk.
As complicated as it sounds, the braneworld picture solves several problems in physics. For example, theoretical physicists Lisa Randall, of Harvard University, and Raman Sundrum, of the University of Maryland, proposed a version of the braneworld that explains an asymmetry in subatomic forces by suggesting the existence of other branes parallel to our own. But it's not enough for a theory to explain facts we already know — it has to make new predictions that can be tested experimentally. In the case of the Randall-Sundrum model, such tests could involve measuring gravitational waves emitted by black holes linking one brane to another.
2. The Big Splat
Artist's impression of multiple braneworlds. When two collide, they may create a new universe. (Image credit: NASA)
3. Plasma-filled cosmos
(Image credit: MARK GARLICK/SCIENCE PHOTO LIBRARY via Getty Images)
The CMB looks virtually the same in every direction, which can't be explained if the universe has always expanded at its current rate. Many scientists believe it went through a brief period of extremely rapid "inflation" a fraction of a second after the Big Bang, suddenly ballooning in size from a subatomic scale to several light-years.
4. The holographic universe
(Image credit: Shutterstock)
Think of a security hologram. This is basically a two-dimensional object encoding a full three-dimensional image. According to this theory, the whole three-dimensional universe may be "encoded" on its two-dimensional boundary. It may not sound as exciting as living inside a simulation, but it has the advantage that it's a scientifically testable theory — research in 2017 from the University of Southampton, U.K., showed it was consistent with the observed pattern of CMB fluctuations.
5. The steady-state universe
(Image credit: Shutterstock)
6. The multiverse
Is our universe just one bubble in a vast multiverse? (Image credit: VICTOR DE SCHWANBERG/SCIENCE PHOTO LIBRARY via Getty Images)
The theory gets even stranger, because there's no reason other universes should have the same laws of physics as ours — some might have stronger gravity, or a different speed of light. Although we can't observe the other universes directly, one of them could conceivably collide with our own. Scientists have even suggested the "cold spot" in the CMB is the imprint of such a collision.
7. We got gravity wrong
Is our galaxy surrounded by dark matter, or is the theory of gravity wrong? (Image credit: European Space Observatory)
There are two possible solutions. The standard one — favored by most scientists — is that the universe contains unseen dark matter, which provides the missing gravity. The maverick alternative is that our theory of gravity is wrong, and should be replaced by something called Modified Newtonian Dynamics (MOND), scientists proposed in 2002 in the journal Annual Review of Astronomy and Astrophysics. The two options — MOND and dark matter — are equally consistent with observations, but are yet to be proven. More experiments are needed.
8. Superfluid space-time
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Even if space only has three dimensions, there's still a fourth dimension in the form of time, so we can visualize the universe existing in four-dimensional space-time. According to some theories, like one proposed by Stefano Liberati of the International School for Advanced Studies and Luca Maccione of Ludwig Maximilian University, in the Physics Review Letters journal, this isn't just an abstract frame of reference containing physical objects like stars and galaxies, but a physical substance in itself, analogous to an ocean of water. Just as water is made up of countless molecules, space-time — according to this theory — is made up of microscopic particles on a deeper level of reality than our instruments can reach.
The theory visualizes space-time as a superfluid having zero viscosity. An odd property of such fluids is that they can't be made to rotate in a wholesale fashion, like an ordinary liquid does when you stir it. They break up into tiny vortices — which in the case of superfluid space-time, may be the seeds from which galaxies form.
9. Simulation theory
According to some philosophers, the universe is a computer-generated illusion projected into our brains. (Image credit: Mads Perch via Getty Images)
So far, all the theories have come from scientists — but here's one from the philosophers. If all of the information about the universe comes into our brains via our senses and scientific instruments, who's to say it isn't all a cleverly designed illusion? The entire universe might be nothing but an ultra-sophisticated computer simulation. It's an idea that was popularized by the "Matrix" movies, but as outlandish as the idea sounds, some philosophers take it seriously. However, it fails the test of a true scientific theory, because there's no way it could be proved true or false.
10. Cosmic ego-trip
(Image credit: Jose A. Bernat Bacete via Getty Images)
The laws of physics involve a handful of fundamental constants that determine the strength of gravity, electromagnetism and subatomic forces. As far as we know, these numbers could have any possible value — but if they departed even slightly from the values they actually have, the universe would be a very different place. Most importantly for us, life as we know it — including, of course, ourselves — couldn't possibly exist. Some people see this as evidence that the universe was consciously designed in order for human-like life to evolve — the so-called self-centered anthropic theory, proposed by Nick Bostrom in his book, "Anthropic Bias."
This article was adapted from a previous version published in How It Works magazine, a Future Ltd. publication.
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