Whether life exists elsewhere in our universe is a long standing mystery. But for some scientists, there’s another interesting question: could there be life in a universe significantly different from our own? Science fiction has often explored other universes such as those of alternate history (where the South won the Civil War and not the North for example). Science fiction has also explored universes where the laws of physics are different. In this case scientists have explored this concept and have come up with some interesting extrapolations.
Whether life exists elsewhere in our universe is a long standing mystery. But for some scientists, there’s another interesting question: could there be life in a universe significantly different from our own? Science fiction has often explored other universes such as those of alternate history (where the South won the Civil War and not the North for example). Science fiction has also explored universes where the laws of physics are different. In this case scientists have explored this concept and have come up with some interesting extrapolations.
!ADVERTISEMENT!A definitive answer is impossible, since we have no way of directly studying other universes. But cosmologists speculate that a multitude of other universes exist within a multiverse, each with its own laws of physics. Recently physicists at MIT have shown that in theory, alternate universes could be quite congenial to life, even if their physical laws are very different from our own.
In work recently featured in a cover story in Scientific American, MIT physics professor Robert Jaffe, former MIT postdoc, Alejandro Jenkins, and recent MIT graduate Itamar Kimchi showed that universes quite different from ours still have elements similar to carbon, hydrogen, and oxygen, and could therefore evolve life forms quite similar to us. Even when the masses of the elementary particles are dramatically altered, life may find a way.
Modern cosmology theory holds that our universe may be just one in a vast collection of universes known as the multiverse. The multiverse is the hypothetical set of multiple possible universes (including our universe) that together comprise everything that physically exists: the entirety of space and time, all forms of matter, energy and momentum, and the physical laws and constants that govern them. Each universe will have some variation of the laws of physics.
In this view, “nature gets a lot of tries; the universe is an experiment that’s repeated over and over again, each time with slightly different physical laws, or even vastly different physical laws,†says Jaffe.
Some of these universes would collapse instantly after forming; in others, the forces between particles would be so weak they could not give rise to atoms or molecules. However, if conditions were suitable, matter would coalesce into galaxies and planets, and if the right elements were present in those worlds, intelligent life could then evolve.
Some physicists have theorized that only universes in which the laws of physics are just right could support life, and that if things were even a little bit different from our world, intelligent life would be impossible. In that case, our physical laws might be explained anthropically, meaning that they are as they are because if they were otherwise, no one would be around to notice them.
Jaffe and his collaborators felt that this proposed anthropic explanation should be subjected to a more careful scrutiny, and decided to explore whether universes with different physical laws could support life.
This is a hard question to answer because of the number of variables. The authors decided to specialize in universes with nuclear and electromagnetic forces similar enough to ours that atoms exist.
Although bizarre life forms might exist in universes different from ours, Jaffe and his collaborators decided to further focus on only life based on carbon chemistry. They further defined that as acceptable for those universes in which stable forms of hydrogen, carbon and oxygen would exist.
“If you don’t have a stable entity with the chemistry of hydrogen, you’re not going to have hydrocarbons, or complex carbohydrates, and you’re not going to have life,†says Jaffe. “The same goes for carbon and oxygen. Beyond those three we felt the rest is detail."
They set out to see what might happen to those elements if they altered the masses of elementary particles called quarks. There are six types of quarks, which are the building blocks of protons, neutrons and electrons which then make up atoms.
In our universe, the down quark is about twice as heavy as the up quark, resulting in neutrons that are 0.1 percent heavier than protons. Jaffe and his colleagues modeled one family of universes in which the down quark was lighter than the up quark, and protons were up to a percent heavier than neutrons. In this scenario, hydrogen would no longer be stable, but its slightly heavier isotopes deuterium or tritium could be. An isotope of carbon known as carbon 14 would also be stable, as would a form of oxygen, so the organic reactions necessary for life would then be possible though in a slightly different form.
The team found a few other congenial universes, including a family where the up and strange quarks have roughly the same mass (in our universe, strange quarks are much heavier and can only be produced in high energy collisions), while the down quark would be much lighter. In such a universe, atomic nuclei would be made of neutrons and a hyperon called the “sigma minus,†which would replace protons.
Obviously other quarks could vary and the ultimate complexity of interactions are very difficult to predict because physicists are limited in their ability to predict the consequences of changing most other physical laws and constants.
A group of researchers at Lawrence Berkeley National Laboratory has done related studies examining whether congenial universes could arise even while lacking one of the four fundamental forces of our universe (in this case the weak nuclear force)which enables the reactions that turn neutrons into protons, and vice versa. The researchers showed that tweaking the other three fundamental forces could compensate for the missing weak nuclear force and still allow stable elements to be formed.
All of this is really working with only simple changes in the laws of physics and the concept of life. Silicon, for example, has been suggested occasionally as an alternate to carbon based life forms. With alternate laws of physics, there may be many other options for life than in our universe.
In the end, there is no way to know for sure what other universes are out there, or what life they may hold. But that will likely not stop physicists or science fiction writers from exploring the possibilities, and in the process learning more about our own universe.
For further information: http://web.mit.edu/newsoffice/2010/multiple-universes.html or http://www.scientificamerican.com/article.cfm?id=looking-for-life-in-the-multiverse
