No, we haven’t finally found evidence for a parallel Universe – Big Think

For some of us, the idea of parallel Universes sparks our wildest dreams. If there are other Universes where certain events had different outcomes where just one crucial decision went a different way perhaps there could be some way to access them. Perhaps particles, fields, or even people could be transported from one Universe to another, enabling us to live in a Universe thats better, in some ways, than our own. These ideas have a foothold not only in science fiction, but in theoretical physics as well, from the infinity of possible outcomes from quantum mechanics to ideas related to the Multiverse.

But do these ideas have anything to do with observable, measurable reality? Recently, a claim has surfaced asserting that weve found evidence for parallel Universes from the ANtarctic Impulsive Transient Antenna: ANITA. Its true: the experiment found evidence for cosmic ray particles thats quite difficult to explain using only conventional physics. But to leap to the most fantastical, outlandish, revolutionary explanation is absolutely premature. In all fields of science, we have to take tremendous care not to fool ourselves. We must endeavor to knock down any new, wild hypotheses, and instead make sure that known laws of nature cant conceivably explain what were seeing.

Science is about being appropriately skeptical, and when we take that approach, we see that the evidence for a parallel Universe all but evaporates.

From a physics point of view, parallel Universes are one of those intriguing ideas that captures our imaginations, and compels us to consider their existence, but at the same time, its an idea thats very difficult to test. Parallel Universes first arose in the context of quantum physics, which is notorious for having unpredictable outcomes even if you know everything possible about how you set up your system. If you take a single electron and shoot it through a double slit, you can only know the probabilities of where it will land; you cannot predict exactly where it will show up.

One remarkable idea known as the many-worlds interpretation of quantum mechanics postulates that all the outcomes that can possibly occur actually do happen, but only one outcome can happen in each Universe. It takes an infinite number of parallel Universes to account for all the possibilities, but this interpretation is just as valid as any other. There are no experiments or observations that rule it out.

A second place where parallel Universes arise in physics is from the idea of the Multiverse. Our observable Universe began 13.8 billion years ago with the hot Big Bang, but the Big Bang itself wasnt the very beginning. A very different phase of the Universe occurred previously to set up and give rise to the Big Bang: cosmological inflation. When and where inflation ends, a Big Bang occurs.

But inflation doesnt end everywhere at once, and the places where inflation doesnt end continue to inflate, giving rise to more space and more potential Big Bangs. Once inflation begins, in fact, its virtually impossible to stop inflation from occurring in perpetuity at least somewhere. As time goes on, more Big Bangs all disconnected from one another occur, giving rise to an uncountably large number of independent Universes: a Multiverse.

The big problem for both of these ideas is that theres no way to test or constrain the prediction of these parallel Universes. After all, if were stuck in our own Universe, how can we ever hope to access another one? We have our own laws of physics, but they come with a whole host of quantities that are always conserved.

Particles dont simply appear, disappear, or transform; they can only interact with other quanta of matter and energy, and the outcomes of those interactions are similarly governed by the laws of physics.

In all the experiments weve ever performed, all the observations weve ever recorded, and all the measurements ever made, weve never yet discovered an interaction that demands the existence of something beyond our own, isolated Universe to explain.

But according to the various reports regarding the ANITA experiments unexpected findings, you may have read that scientists in Antarctica have discovered evidence for the existence of parallel Universes. If this were true, it would be absolutely revolutionary. Its a grandiose claim that would show us that the Universe as we currently conceive of it is inadequate, and theres much more out there to learn about and discover than we ever thought possible.

Not only would these other Universes be out there, but matter and energy from them would have the capability to cross over and interact with matter and energy in our own Universe. Perhaps, if this claim were correct, some of our wildest science fiction dreams would be possible. Perhaps you could travel to a Universe:

So what was the remarkable evidence that demonstrates the existence of a parallel Universe? What observation or measurement was made that brought us to this remarkable and unexpected conclusion?

The ANITA (ANtarctic Impulsive Transient Antenna) experiment a balloon-borne experiment thats sensitive to radio waves detected radio waves of a particular set of energies and directions coming from beneath the Antarctic ice.

This is good; its what the experiment was designed to do! In both theory and in practice, we have all sorts of cosmic particles traveling through space, including the ghostly neutrino. While many of the neutrinos that pass through us come from the Sun, stars, or the Big Bang, some of them come from colossally energetic astrophysical sources like pulsars, black holes, supernovae, or even mysterious, unidentified objects.

These neutrinos also come in a variety of energies, with the most energetic ones (unsurprisingly) being the rarest and, to many physicists, the most interesting. Neutrinos are mostly invisible to normal matter youd have to pass a typical astrophysical neutrino through about a light-years worth of lead to have a 50/50 shot of stopping one so they can realistically come from any direction.

However, most of the high-energy neutrinos that we see arent produced from far away, but are produced when other cosmic particles (also of extremely high energies) strike the upper atmosphere, producing cascades of particles that also result in neutrinos. Some of these neutrinos will pass through the Earth almost completely, only interacting with the final layers of Earths crust (or ice), where they can produce a signal that our detectors are sensitive to.

The rare events that ANITA saw were consistent with a neutrino coming up through the Earth and producing radio waves, but at energies that should be so high that passing through the Earth uninhibited should not be possible. So now, we have to put our skeptical goggles on, and ask some important questions concerning how seriously we should take these observations.

Scientifically, this means that:

So where, in all of this, do the parallel Universes come in?

Because there were only three explanations for what ANITA saw.

Somevery good science ruled out the first option(back in January of 2020), which means its almost certainly the second option. The third? Well, if our Universe cannot violate CPT, maybe this comes froma parallel Universe where CPT is reversed: an explanation thats as unlikely as it is poorly reasoned.

In fact, back in April of 2020, physicist Ian Shoemaker came up with a spectacular but mundane explanation for what ANITA saw: ultra-high-energy cosmic rays could have simply reflected off of certain types of ice at or near the Antarctic surface, creating the illusion that these particles traveled through the Earth from the perspective of ANITA. Remember: in science, we must always rule out all the conventional explanations that dont involve new physics before we resort to a game-breaking explanation. Over the past decade, a number of remarkable claims have been made that have disintegrated upon further investigation. Neutrinos dont travel faster-than-light; we havent found dark matter or sterile neutrinos; cold fusion isnt real; the impossible reactionless engine was a failure.

Theres a remarkable story here thats all about good science. An experiment (ANITA) saw something unexpected, and published their results. A much better experiment (IceCube) followed it up, and ruled out their leading interpretation. It strongly suggested something was amiss with the first experiment, and completely mundane explanations involving no new physics at all could wholly account for the full suite of what weve seen. As always, conducting more science will help us uncover whats truly occurring. For now, based on the scientific evidence we have, parallel Universes will have to remain a dream solely confined to the realm of speculation and science fiction.

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No, we haven't finally found evidence for a parallel Universe - Big Think