How to Study String Theory Using X-Rays | SciShow News

How to Study String Theory Using X-Rays | SciShow News

[ intro ] Generally speaking, astronomers tend to study the biggest stuff
in the universe, while particle physicists study the smallest. But over the last few years, astronomers have done more and more research on a certain prediction made by string theory — one of the most popular unproved ideas
in all of physics. And let’s just say their results haven’t
been very encouraging. The hope was that this might change after a new study from NASA’s Chandra X-Ray
Observatory, which tried to find evidence for string theory
using galaxy collisions. But so far, things aren’t looking promising. This new study was published last month in The Astrophysical Journal, and it has three
key pieces. There’s the string theory. There’s the astronomy. And there’s the family of hypothesized particles that ties them all together: a group called axion-like particles. But first, the string theory. String theory is one of the major candidates for what’s called a “Theory of Everything”: a single framework that could predict the
results of any experiment we could ever do. Our best theories currently split the universe into the big stuff that’s governed by gravity, and small stuff that’s modeled by quantum
mechanics. Both models are great in their own domains, but try to make them overlap, and funky things can happen. For instance, if you try to study gravity on the tiniest
scales, any little bit of gravity should make more
gravity around it. So gravity should make more gravity, should
make more gravity — until you end up with an infinitely dense
point where math doesn’t work. But in string theory, that can’t happen. String theory supposes that all particles are actually made of tiny, vibrating strings. And to make a simplification, since those strings have a sort of length, their interactions can never create a single,
infinitely dense point. And that stops the chaos. Different theorists find different ways to
go from this stringy foundation to a universe like ours, so there are multiple versions of string theory
out there. But many of them require certain kinds of
new, unobserved particles to work. Including some small, super-light ones. They’re known as axion-like particles, or
ALPs. If they exist, ALPs would be so light that they’d hardly
ever bump into any other kind of matter, which would explain why we’ve never seen
one in an experiment. But a lot of researchers still think they’re
out there, because ALPs seem like the perfect missing
pieces to many puzzling aspects of the universe. They’re good candidates for dark matter, they could be why the universe has more matter
than antimatter, and they might even explain why time only
ticks in one direction! But we still haven’t seen them. The good news is, human-run experiments aren’t
the only places to look. According to string theory, ALPs should occasionally turn into photons, or particles of light, as they travel through
a magnetic field, and vice versa. And for astronomers, that’s pretty convenient, because space is full of light and magnetic
fields. So, if you looked at light after it went through
one of these fields, you could look for distortions created by
ALP interference. And if you saw that — well, you’d provide the evidence physicists
have been looking for. Recently, this is exactly what a team of astronomers
and cosmologists tried to do using the Chandra X-Ray Observatory. They weren’t the first to look for ALPs
this way, but their observations let them look more
closely than anyone had before. They used Chandra to look at light from a
galaxy called NGC 1275. It’s about 230 million light-years away, and it’s a galaxy that eats other galaxies. Collisions like that release tons of X-rays, and we can use models to predict what those
rays should look like in an ALP-free universe as they escape the
galaxies’ magnetic fields. In their study, the team compared what they
saw from NGC 1275 with a range of ALP models — because, remember, there’s no one model. Some say ALPs should interact with light a
lot; others say it should be pretty rare. And in the end… well, The light from the galaxy looked exactly like
we’d expect. The team saw no evidence of ALPs in their
data. This doesn’t mean they aren’t out there, but the fact that even a super-sensitive telescope
like Chandra couldn’t find them does effectively eliminate a big range of
possible models. Maybe an even more advanced telescope could
change things in the future. But again, this Chandra study isn’t the
only one of its kind. Over the last couple decades, astronomical teams around the world have looked
for evidence of ALPs in their data, and none have found anything. There are still models out there that fit
everyone’s observations, but the field is thinning out fast — making some scientists increasingly skeptical
about ALPs and some of the string theories that predict
them. So axion-like particles might still exist. But if they do, they probably look pretty
different from what we first expected. Thanks for watching this episode of SciShow
Space News! If you’re interested in astronomy and want
to learn more about the field as a whole, you might enjoy a series from one of our sister
channels, Crash Course. Their Crash Course Astronomy series covers
everything from stars to eclipses to big questions about things like dark energy. It’s hosted by the amazing Phil Plait and
is just a great time. You can check it out after this! [ outro ]


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