Can the stars in alternate universes with different physical constants host potentially habitable planets?
What would stars be like in the other universes? In areas where the strength of the radioactive decay is stronger or weaker than in our cosmos, scientists now that such star systems can often be a habitable place for life as we know it.
The laws of physics in our universe are a number of the fundamental constants, like the speed of light. However, many scientific models have the possibility for the existence of a large ensemble of universes called the multiverse, which might include places where the laws of physics differ.
Many researchers have previously suggested that sufficiently large variations in the laws of physics would result in lifeless universes, so that only small variations in the fundamental constants would be allowed. To investigate this idea further, astrophysicists have explored universes where the nuclear forces can differences and speculated about the possible habitability of these alternative places. [5 Reasons We May Live in a Multiverse]
“We don’t know if other universes exist, and if they do, we are almost certainly not to them,” study lead author Alex Howe, a theoretical astrophysicist at the University of Michigan in Ann Arbor, told Space.com. Still, “by doing this thought experiment, we can help answer a fundamental question — did our universe have to be such as it is, or why? In doing this, we learn more about our own universe,” Howe said.
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The scientists focused on the weak interaction, also known as the weak force and the weak nuclear force. This force is responsible for radioactive decay, for example, causes neutrons to decay into protons, electrons, and electrically neutral particles known as electron antineutrinos.
An important way the scientists measured habitability was to assess whether the worlds in these universes can host liquid water on the surface. There is life virtually wherever there is liquid water on Earth, so the search for life beyond Earth often focuses on the water.
Earlier research found that a universe where the weak force is completely absent, is still habitable. In the new study, the researchers have examined scenarios in which the weak force was still present, but less pronounced than in our universe, as well as the cases where it was stronger.
In universes with a stronger weak force, neutrons would decay faster, so the early universe in that scenario, it would be almost devoid of helium, the researchers said. This is fine when it comes to the level of the water in the universe, because the water consists of hydrogen and oxygen.
In universes with a weaker weak force, neutrons would decay more slowly, which leads to more helium. For a hydrogen to survive without built in larger nuclei, the researchers found a fundamental constant would be smaller. In other words, the ratio of the baryons, protons and neutrons, photons, that light is made of, would have to shrink.
The weak force also plays a role in how stars fuse hydrogen into helium atoms, which can affect how bright, warm, large and with a long life star. In addition, the weak force determines how often neutrinos interact with ordinary matter, which in turn has an effect on how the energy drains from the interior of stars.
Universes with a weaker weak force would have stars with more deuterium, a hydrogen atom with an extra neutron in its nucleus. Deuterium-rich stars would be larger, brighter and redder than the stars in our universe, seems the red giant stars in our universe.
Universes with a stronger weak force would have stars with more helium-3, a helium atom is missing a neutron from the nucleus. These stars would be a bit brighter and larger in diameter than the stars in our universe and it would be a tad shorter life, although they would have similar temperatures.
Although the stars in these universes are slightly different from ours, their similar surface temperatures, luminosities, diameters, and lives do these universes would continue to be potentially habitable over a wide range from the strong to the weak force, according to the researchers.
“The most surprising for me was that in most possible universes, stars, still working in one way or another,” Howe said. “In many possible universes, stars would be even more complex life cycle than in our own, or would it be more favorable to life.”
All in all, “in my opinion, the most important implication is that there are many different ways a universe can live and work, not only in the physics of our own,” Howe said.
Future research may investigate universes with different strengths of the strong nuclear force, the strongest known force between the particles, that binds the protons together in the atomic nuclei, despite their mutual repulsion, Howe said.
The scientists detailed their findings online Sept. 13 in a study accepted by the journal Physical Review D.
Original article on Space.com.