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[♪ INTRO]
By now, you’ve probably seen some news articles
announcing
the discovery of a parallel universe where
time runs backwards.
I’m sorry to say we have discovered no such
thing.
But let’s look at what the research behind
that announcement was really all about,
and how the story got so twisted.
The whole thing started a few years ago,
when a radio telescope known as ANITA made
two really weird detections.
ANITA sits in a balloon over Antarctica, and
its job is to
detect high-energy particles called cosmic
rays that rain down from space.
It does that by picking up radio pulses that
get emitted
when cosmic rays interact with Antarctic ice
or the atmosphere.
But between 2016 and 2018, ANITA detected
something strange.
It picked up two signals that looked like
they’d been triggered by neutrinos,
which are a type of cosmic ray, but weirdly,
they were coming up from the ground, instead
of down from space.
Now, because neutrinos are so small and have
no charge,
they can travel straight through a lot of
matter without interacting with it.
So the idea that they’d originally come
from space and traveled
all the way through the Earth wasn’t inconceivable,
but there was one problem.
By working back from the detections, the scientists
working on the project
found that the neutrinos that produced those
signals must have had a ton of energy.
And according to the Standard Model,
which is basically all the math behind our
current understanding of particle physics,
neutrinos with higher energies are more likely
to interact with matter.
So the Earth should have absorbed these neutrinos
before they reached the surface.
If the detections were real, that could overturn
the Standard Model
and everything we thought we knew about the
subatomic world.
Because even though neutrino interactions
are just one part of the Standard Model,
it’s kind of like a Jenga tower: Pull out
one piece of math, or one piece of evidence,
and the whole thing comes crashing down.
But the Standard Model has held up to a lot
of tests,
so the authors weren’t so quick to suggest
it was wrong.
As another possibility, they suggested that
maybe a bunch of neutrinos
had come from a really strong, focused source,
like a massive supernova.
Because even though no single neutrino with
that much energy
is likely to pass through Earth, if you had
enough of them,
then the odds are a little better that at
least a few might make it all the way through.
Still kind of a long shot, but if the idea
was right,
we wouldn’t have to completely redo all
of particle physics.
But before the team even had a chance to investigate
that possibility, another paper,
published in 2018, suggested that something
else could explain those weird detections,
and it was also a long shot: a thing called
the CPT-symmetric universe.
CPT stands for “charge, parity, and time,”
and CPT symmetry means that
the laws of physics should hold if all the
particles in the universe
flipped their charges and spacetime were a
mirror-image of itself.
But it’s purely hypothetical.
All it says is that, if all you consider is
the math, it’s hypothetically possible
to have a universe that’s full of antimatter
where time moves backward.
And the scientists suggesting that these cosmic
rays might have come from a
CPT-symmetric universe weren’t saying that
it was a sure thing or even a likely thing.
They were just saying that the math checks
out,
and that if a CPT-symmetric universe exists,
it would have particles that behave the opposite
of particles we’re familiar with.
And they suggest that one of those particles
could potentially,
potentially, explain these upward-moving cosmic
rays.
So, at this point, scientists had a weird
observation
and three possible explanations that all seemed
unlikely:
Either our understanding of particle physics
is fundamentally flawed,
or this super-energetic supernova event sent
some cosmic rays
all the way through the Earth, or there’s
a parallel universe that’s a mirror image of ours.
Earlier this year, scientists ruled out the
supernova explanation,
because data from a second cosmic ray detector
in Antarctica
failed to find evidence backing up that scenario.
They suggested that maybe the observations
had just been an error,
or maybe they were a sign of some weird physics.
But the explanation could also be something
no one has thought of yet.
Unfortunately, when reporters covered that
paper,
some of them highlighted the CPT explanation,
and then other outlets went running with that
angle.
In reality, there’s still no answer to the
mystery,
but there’s also no evidence for a parallel,
mirror universe.
Thanks for watching this episode of SciShow
Space News!
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a parallel universe where time runs backwards,
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[♪ OUTRO]
