Life beyond our universe

MIT physicists explore the possibility of life in universes with laws different from our own.


Whether life exists elsewhere in our universe is a longstanding mystery. But for some scientists, there’s another interesting question: could there be life in a universe significantly different from our own?

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, 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.

“You could change them by significant amounts without eliminating the possibility of organic chemistry in the universe,” says Jenkins.

Pocket universes

Modern cosmology theory holds that our universe may be just one in a vast collection of universes known as the multiverse. MIT physicist Alan Guth has suggested that new universes (known as “pocket universes”) are constantly being created, but they cannot be seen from our universe.

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 instants 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 evolve.

Some physicists have theorized that only universes in which the laws of physics are “just so” 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 more careful scrutiny, and decided to explore whether universes with different physical laws could support life.

This is a daunting question to answer in general, so as a start they decided to specialize to 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 focus on life based on carbon chemistry. They defined as “congenial to life” 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. The MIT team focused on “up”, “down” and “strange” quarks, the most common and lightest quarks, which join together to form protons and neutrons and closely related particles called “hyperons.”

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 be possible.

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. They published their findings in the journal Physical Review D last year.

Fundamental forces

Jaffe and his collaborators focused on quarks because they know enough about quark interactions to predict what will happen when their masses change. However, “any attempt to address the problem in a broader context is going to be very difficult,” says Jaffe, 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 — 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.

That study and the MIT work are different from most other studies in this area in that they examined more than one constant. “Usually people vary one constant and look at the results, which is different than if you vary multiple constants,” says Mark Wise, professor of physics at Caltech, who was not involved in the research. Varying only one constant usually produces an inhospitable universe, which can lead to the erroneous conclusion that any other congenial universes are impossible.

One physical parameter that does appear to be extremely finely tuned is the cosmological constant — a measure of the pressure exerted by empty space, which causes the universe to expand or contract. When the constant is positive, space expands, when negative, the universe collapses on itself. In our universe, the cosmological constant is positive but very small — any larger value would cause the universe to expand too rapidly for galaxies to form. However, Wise and his colleagues have shown that it is theoretically possible that changes in primordial cosmological density perturbations could compensate at least for small changes to the value of the cosmological constant.

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 from exploring the possibilities, and in the process learning more about our own universe.


Topics: Physics

Comments

is excellent information on other phases of universes, universes with investigating whether different laws of physics could support life
When I was younger, I actually used to contemplate this--whether life could exist without the exact conditions of the Earth--because it seemed like it would make other life much more probable. I was around 10, though, so I obviously didn't think as in depth as altering quarks.
Isn't this a waste of time. Where is there data supporting a multiverse?
If we cannot communicate with these other universes, what is the point in speculating whether or not life exists in this universes. After all we have no direct proof that life exists outside the Earth. Just another way physicists can interest the general public in order to get public interest and/or funding.
If you have a final theory or a complete theory of quantum gravity, then you can spout off all that you want to. But you are just telling us fairy-tales without this justification. What's happened to science that physics is a free-for-all, and the scientific method is not respected? Very sad.
Well, if scientists have had that attitude of not looking beyond the horizon we would still be hanging up on trees. So we did not verify if life exists beyond Earth (well, for the sake of argument we don't even know what life is exactly, as so far we do have one sample of what might be life - meaning us, and things that grow and crawl around us), we don't know if another universes do exist, and we do not know how we could communicate with them. Fortunately limits like that did not stop scientists in exploring possibilities and look around yourself. I'll bet that while you are reading this on the monitor in your reach there are dozens of things once considered impossible.
So, that makes some sense, but that's a little difficult to be testified by experiment. When I was young, I regarded the universe as one surrounded by another. Has no edge!
The theory of multiple universes gives rise to many questions: 1. If ours is not the only universe and there is a multiverse, what does the whole picture look like? 2. Is there another level of reality beyond the multiverse such as multi-multiverses? 3. What conditions give rise to a big bang to create a universe? 4. How old is all this fabric? 5. How big is all this fabric? 6. Are strings the smallest element? Or are the strings made from something smaller yet? 7. Is the dark energy actually the gravitional pull from other universes? 8. How much matter and energy is out there in reality? 9. How stable is our universe? And for how long? Perhaps, many more.
I'm suprised many people here are questioning the importance of what now is just speculation. Speculation later turns into philosophy and eventually turns into science. Perhaps one day we will find definitively there is a multiverse and even learn the laws which govern another universes. Could you imagine the possibilities of what we could do here if we found such knowledge? The same sort of naysaying would have occurred 3,000 years ago if someone predicted that we could one day have the types of media technology of today, fly to the moon, regrow someone's organs using stem cells, etc. The pursuit of knowledge is hardly a waste of time. Push the boundaries, evolve and let tomorrow be a better day.
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