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| Photo: VNT |
1. Braneworld
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, according to Live Science.
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.
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| Photo: Live Science |
2. Cosmic ego-trip
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,” said How it works magazine.
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| Photo: Live Science |
3. The Big Splat
In the far future, galaxies will eventually drift so far apart that light from one can never reach another. In fact, as stars get old and die, there will come a time when there’s no light – or heat – left. The universe will be a dark, cold, empty void. It sounds like the end of everything, but according to one theory, it’s actually the beginning of the next universe in an endlessly repeating cycle.
Remember the braneworld theory? What happens when one cold, empty brane collides with another – which, given enough time, it’s bound to do eventually. Cosmologists Neil Turok and Paul Steinhardt believe such a collision would generate enough energy to create a whole new universe. They call this the ‘ekpyrotic theory’, though physicist Michio Kaku has more evocatively dubbed it the ‘Big Splat’.
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| Photo: UCSC |
4. Plasma-filled cosmos
The Big Bang remains the preferred theory of many scientists, supported by two key observations — the expansion of the universe and the cosmic microwave background (CMB). Immediately after the Big Bang, the universe was much smaller and hotter, filled with a glowing plasma like the sun. We still see the end of this super-hot phase in the form of a sea of radiation filling the whole of space. The expansion of the universe over the intervening billions of years has cooled the radiation down to minus 454 degrees Fahrenheit (minus 270 degrees Celsius), but it is still detectable by radio telescopes.
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.
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| Photo: World Science Festival |
5. Superfluid space-time
One of the most outlandish new theories of cosmology is that space-time is actually a superfluid substance, flowing with zero friction. Then if the universe is rotating, superfluid spacetime would be scattered with vortices, according to physicists Pawel Mazur of the University of South Carolina and George Chapline at Lawrence Livermore lab in California – and those vortices might have seeded structures such as galaxies.
Mazur suggests that our universe might have been born in a collapsing star, where the combination of stellar matter and superfluid space could spawn dark energy, the repulsive force that is accelerating the expansion of the universe, according to New Scientist.
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| Photo: Live Science |
6. The holographic universe
Think about security holograms. This is basically a 2D object that encodes a complete 3D image. According to this theory, the entire three-dimensional universe can be “encoded” at its two-dimensional boundaries.
It may not sound as exciting as living in a simulation, but it has the advantage of being a scientifically verifiable theory. University of Southampton, United Kingdom has shown that it is consistent with the observed pattern of CMB variability.
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| Photo: Science News |
7. Gravity reaches out
Dark matter might not really be “stuff” – it could just be a misleading name for the odd behavior of gravity. The theory called MOND (modified Newtonian dynamics), suggests that gravity does not fade away as quickly as current theories predict.
This stronger gravity can fill the role of dark matter, holding together galaxies and clusters that would otherwise fly apart. A new formulation of MOND, consistent with relativity, has rekindled interest in the idea, although it may not fit the pattern of spots in the cosmic microwave background.
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| Photo: Live Science |
8. The steady-state universe
The Big Bang is an evolutionary theory in which the universe changes in appearance as it expands. It was denser in the past, and it will become less dense in the future. Not all scientists were happy with that, so they came up with a way for the density to remain constant, even in an expanding universe. It involves the continuous creation of matter at the rate of about three hydrogen atoms per cubic meter per million years. This model fell out of favor with the discovery of the CMB, which it can’t easily explain.
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| Photo: Live Science |
9. The multiverse
In the conventional view of the Big Bang, in order to explain the uniformity of the CMB, it’s necessary to postulate an early spurt of superfast expansion known as inflation. Some scientists believe that when our universe dropped out of this inflationary phase, it was just one tiny bubble in a vast sea of inflating space. In this theory, called ‘eternal inflation,
other bubble universes are constantly popping up in other parts of the inflationary sea, with the whole ensemble making up a ‘multiverse’.
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, it’s conceivable one of them could collide with our own. It’s even been suggested the ‘cold spot’ in the CMB is the imprint of such a collision.
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| Photo: Unreveal Files |
10. Simulation theory
Maybe our universe isn’t real. Philosopher Nick Bostrom has claimed that we are probably living inside a computer simulation. Assuming it ever becomes possible to simulate consciousness, then presumably future civilizations would try it, probably many times over.
Most perceived universes would be simulated ones – so chances are we are in one of them. In that case, perhaps all those cosmological oddities such as dark matter and dark energy are simply patches, stuck on to cover up early inconsistencies in our simulation.
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| Photo: Emergent |
11. Evolving universes
When the matter is compressed to extreme densities at the center of a black hole, it might bounce back and create a new baby universe. The laws of physics in the offspring might differ slightly, and at random, from the parent – so universes might evolve, suggests Lee Smolin of the Perimeter Institute in Waterloo, Canada.
Universes that make a lot of black holes have a lot of children, so eventually, they come to dominate the population of the multiverse. If we live in a typical universe, then it ought to have physical laws and constants that optimize the production of black holes. It is not yet known whether our universe fits the bill.
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| Photo: Live Science |
12. Fast light
Why do opposite sides of the universe look the same? It’s a puzzle because the extremes of today’s visible universe should never have been in touch. Even back in the early moments of the big bang, when these areas were much closer together, there wasn’t enough time for light – or anything else – to travel from one to another.
There was no time for temperature and density to get evened out; and yet they are even. One solution: lightly used to move much faster. But to make that work could mean a radical overhaul of Einstein’s theory of relativity.
