What To Do If You Encounter A Visitor From Another Universe

If parallel Universes or the multiverse are real, we might someday encounter a visitor who hails from another one. Here’s what to do.

There are a lot of things that are inherent to our Universe that we take for granted. We rarely think about the laws of physics being what they are, the fundamental constants having the values that they do, or matter predominating over antimatter. Yet these are fundamental properties about our Universe. If they were different, our Universe that we inhabit would be an extremely different place from the way it is today.

However, our Universe may not be the only one out there. In fact, there are compelling reasons to believe that our Universe is just one of many, all of which make up a much larger Multiverse. If this is true, then it’s possible that other Universes not only have their own inhabitants, some of whom may be intelligent and technologically advanced, but different rules governing their existence. Even though they may be benign, meeting one could lead to catastrophe. Here’s how — using physics — you can ensure your survival.

A CP-symmetry transformation swaps a particle with the mirror image of its antiparticle. The LHCb collaboration has observed a breakdown of this symmetry in the decays of the D0 meson (illustrated by the big sphere on the right) and its antimatter counterpart, the anti-D0 (big sphere on the left). When the events occur, each one decays into other particles (smaller spheres) differently, at a small (~0.1%) but significant level, the first time such an asymmetry has been observed in charmed particles. (CERN)

If we witnessed someone simply pop into existence, your first worry might be that they’re made out of antimatter, rather than matter. The laws of physics need not be different from our own for this to occur; they’d simply need the cosmic processes that created more matter than antimatter in our Universe to be reversed. If the scales were tipped in the opposite direction for us, we’d never know.

Changing particles for antiparticles and reflecting them in a mirror simultaneously represents CP symmetry. If the anti-mirror decays are different from the normal decays, CP is violated. Time reversal symmetry, known as T, is violated if CP is violated. The combined symmetries of C, P, and T, all together, must be conserved under our present laws of physics, with implications for the types of interactions that are and aren’t allowed. (E. SIEGEL / BEYOND THE GALAXY)

But that’s okay; there are physical signs of matter (or antimatter) that go beyond a simple sign convention. In our Universe, there are probabilities that certain mesons (neutral composite particles) which contain strange, charm, or bottom quarks will spontaneously transform into their antimatter counterparts, swapping quarks for antiquarks and vice versa.

If we ask a visitor for their CP-violation measurements, we can know immediately whether they’re matter or antimatter. If we really want to be sure, we can throw an apple their way; if it annihilates with their hull, they were antimatter all along.

In the absence of a magnetic field, the energy levels of various states within an atomic orbital are identical (L). If a magnetic field is applied (R), however, the states split according to the Zeeman effect. The exact energy level differences that any atom or molecule exhibits are highly dependent on the fundamental constants of the Universe. If they vary from Universe to Universe, we’d be able to identify someone by their absorption and emission spectra. (EVGENY AT ENGLISH WIKIPEDIA)

What if the fundamental constants are different for their Universe as compared to our Universe? If that were the case, their matter would behave differently. Change the masses of the particles or the strength of their interactions, and the properties of matter itself will change. Even changing the mass of a particle that we rarely think about as relevant to our Universe, like a top quark, would subtly change the mass of a proton.

If any constants were to change, then the properties of atoms and the molecules they make up would be different. Atomic transitions would be slightly (or significantly) shifted, and what gets emitted or absorbed by our hydrogen atoms wouldn’t be absorbed or emitted by theirs, respectively. Simply observing the reflected and absorbed/re-emitted sunlight off of their hulls spectroscopically would tell us whether their physical constants were the same as ours or not.

The visible light spectrum of the Sun, which helps us understand not only its temperature and ionization, but the abundances of the elements present. The long, thick lines are hydrogen and helium, but every other line is from a heavy element. If someone came from a different Universe, their atoms and molecules would have their own unique absorption and emission signatures that might be different from our own. (NIGEL SHARP, NOAO / NATIONAL SOLAR OBSERVATORY AT KITT PEAK / AURA / NSF)

But what if they were even more fundamentally different than we are? What if their Universe obeyed entirely different laws of physics from our own? Sure, the matter/antimatter tests and the fundamental constant tests would be important to perform, but they don’t fully encapsulate the ways that disparate Universes could be different from one another.

For example, it’s possible that there are different fundamental forces, particles, and interactions in their Universe as compared to ours. They may be made out of some form of material that behaves like matter, antimatter, or something entirely new. If they’ve mastered inter-Universe travel, there’s a good chance they know even more fundamental physics than we do. Perhaps, if we shared with them what we knew, they’d share with us how their understanding superseded our own?

The Standard Model of particle physics accounts for three of the four forces (excepting gravity), the full suite of discovered particles, and all of their interactions. Whether there are additional particles and/or interactions that are discoverable with colliders we can build on Earth is a debatable subject, and whether these laws and rules are the same or different in other Universes is unknown at this point. (CONTEMPORARY PHYSICS EDUCATION PROJECT / DOE / NSF / LBNL)

Do the fundamental forces, of which we have four, unify at higher energies? We know that the electromagnetic force and the weak nuclear force unify in our Universe at approximately temperatures of a few quintillion kelvin, and it’s possible that at still higher temperatures the strong or gravitational forces will unify as well.

But what about in another Universe? Even if they have the same fundamental forces, do they unify or not unify in the same way? Do their unification symmetries break at the same energies ours do, or different ones? These are fundamental questions that might lead to enormous differences in the rules our particles play by today, and are something we’d want an answer to before coming into potentially deadly contact with them.

The idea of unification holds that all three of the Standard Model forces, and perhaps even gravity at higher energies, are unified together in a single framework. This idea is powerful, has led to a great deal of research, but is a completely unproven conjecture. Nevertheless, many physicists are convinced this is an important approach to understanding nature, and it has led to some interesting, generic, and testable predictions. It may even be true in some Universes and not others. (© ABCC AUSTRALIA 2015 NEW-PHYSICS.COM)

Are they three-dimensional creatures like we are, or do they live in a different number of dimensions?

If they appear like Gods to us — with the ability to teleport faster-than-light, to reach inside us and rearrange our internal organs, and/or the capability of pulling us out of what we know as existence (and into a higher dimension) — then they likely can access four or more spatial dimensions, as opposed to just the three we know.

On the other hand, if they existed in two or fewer dimensions, we would appear God-like to them in a similar fashion. The number of dimensions in our Universe is highly constrained and very well-measured, but we simply don’t know what other Universes may hold.

If extra dimensions exist, they must be very small in size. Even with the largest values allowed, the decay time of a black hole created at the LHC would still only be increased to a tiny fraction of a second. But if extra dimensions were real, the possibility would suddenly exist to exit our 3D universe, traverse through the fourth spatial dimension, and re-enter at a completely disconnected point in spacetime. If a creature from another Universe occupied a number of spatial dimensions that was different from 3, we’d be able to find out. (FERMILAB TODAY)

Does mass mean the same thing in their Universe as it does in our Universe? We have a bold way to test this for ourselves: through Einstein’s Equivalence Principle. If you have an object with mass and you exert a force on it, it will accelerate according to Newton’s famous law: F= ma.

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On the other hand, if you have an object with mass and you observe the effects of gravitation on it, it will exert a gravitational force that’s directly related to the mass of the object. In Newtonian gravity, that’s F = GMm/r², where the m in both equations are interchangeable. (It’s more complicated in General Relativity, where space is curved and that curvature causes an acceleration, but the result is still proportional to m.)

The identical behavior of a ball falling to the floor in an accelerated rocket (left) and on Earth (right) is a demonstration of Einstein’s equivalence principle. Although measuring the acceleration at a single point shows no difference between gravitational acceleration and other forms of acceleration, measuring multiple points along that path would show a difference, due to the uneven gravitational gradient of the surrounding spacetime. (WIKIMEDIA COMMONS USER MARKUS POESSEL, RETOUCHED BY PBROKS13)

But are these two types of masses — inertial mass for F = ma and gravitational mass for the other one — the same in all Universes? Or might there be a non-equivalence in another Universe?

If that’s the case, it would mean that there would be a fundamental difference between two different types of acceleration. Thrust, such as that caused by a rocket, would result in a different change in motion through the Universe than simply accelerating under the influence of gravity. While these two types of masses and the accelerations they cause (gravitational and non-gravitational) are known to be equivalent to better than one part in a trillion in our Universe, we simply don’t know that this will be the case in another Universe. Anything that’s not forbidden from being different may turn out to be different, after all.

Instead of an empty, blank, 3D grid, putting a mass down causes what would have been ‘straight’ lines to instead become curved by a specific amount. In General Relativity, we treat space and time as continuous, but all forms of energy, including but not limited to mass, contribute to spacetime curvature. If the acceleration due to gravity is different from inertial acceleration, this would violate the equivalence principle.(CHRISTOPHER VITALE OF NETWORKOLOGIES AND THE PRATT INSTITUTE)

Of course, if all we could do is send a message, it might be best to send something short and easily comprehensible. We might simply tell them, “this Universe contains electrons,” and convey to them what that means. If we share with them the value of electric charge, how electrons and nuclei assemble to form atoms, what the wavelengths they create based on those atomic transitions are, and what the mass ratios of different fundamental and composite particles are, plus a little information about CP-violation, they could immediately know whether their rules and laws were the same as ours.

Is it safe to physically interact with such an alien? Presumably, if they’re the ones capable of inter-Universe travel, they’re the ones who’ll know the answer. But we must inform them of what we know. If it’s unsafe, we need to get them that info, and find it out for ourselves, before we do anything else.

Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.