At the beginning of the 20th century
Many scientists started thinking that Physics was pretty much over
Surely we have a few unsolved mysteries left but it seemed like they could all be ironed out with better measurements, or maybe with very slight tweaks to what was already known
The problem was, those mysteries didn't go away with better measurements and slight tweaks
They led to fundamental revolutions in our understanding of nature
Huge, important things, like Relativity and Quantum Mechanics
Now that we've discovered those things, though, It might sometimes feel like there are, once again, just a few small problems left for physicists to solve before we can say we know everything
About how the universe works
Here are 5 of those problems that are actually a really big deal
And aren't going to go down without a fight
Neutrinos are tiny sub-atomic particles
There are TRILLIONS of them flying through you every second
But they hardly ever hit one of your atoms
Like, even a 14,000 Metric Ton neutrino detector will only detect a few neutrinos a day
As strange as that might be, Physicists mostly understand why Neutrinos don't often interact with ordinary matter
What they don't understand, is why Neutrinos have mass
Or why that mass is so small
Particle Physicists use the standard model
Which uses math to describe how every known particle interacts with every other known particle
It's one of the most successful models in history
The Standard Model correctly predicts the results of literally trillions of experiments
Now the problem is, the Standard model also predicts that Neutrinos shouldn't have any mass
But in the 1990's, Physicists studying Neutrinos coming from the sun realized that Neutrinos had to have mass
There are a few different kinds of Neutrinos, and the researchers found that the Neutrinos coming from the sun were switching types
But they would need mass to be able to do that switching
Which means that the standard model, has a pretty big hole in it
Now, there IS a way of changing the equation used in the Standard model so that it includes Neutrinos with mass
But on it's own, the fact that Neutrinos have mass doesn't necessarily have to be a dealbreaker
But, Neutrinos masses are also incredibly tiny compared to every other fundamental particle out there
Electrons are the next lightest particles we've found, and they're still somewhere between 126,000 and 600 million times heavier than the lightest Neutrinos
That huge gap makes a lot of Physicists think that fitting Neutrinos with mass into the current Standard Model, is a little bit like shoving sugar packets under the leg of a wobble table, and saying you fixed it
There are a few other possible explanations out there that also fit with the standard model, and so far, we haven't found any solid evidence to support them
Other Physicists think that we need to throw out the Standard model altogether, and turn to new models to explain the mysterious mass
Another possible solution to the Neutrino mass problem could help solve a second mystery
Why is there so much matter in the universe?
See, Matter has a sort of twin called Antimatter
Antimatter particles are just like regular matter particles, except they have the opposite charge
So regular matter has electrons, for example, which have a negative charge
But antimatter has what are called positrons, which are just like electrons except with a positive charge
and whenever a particle of matter meets its corresponding particle of antimatter, they annihilate each other in a big explosion
The problem is, Matter and Anti-matter act the same in a lot of ways, as long as they're kept separate from each other
Like, when we do experiments in particle accelerators and produce particles of matter, we produce particles of antimatter, too
Antimatter can even make atoms, just like normal matter can
The laws of Physics just don't seem to prefer one over the other
But when we look out into the universe, all we see is ordinary matter
Like the stuff down here on Earth
There are no Antimatter stars, no Antimatter galaxies, and no Antimatter dust clouds
If there were, they'd occasionally run into similar pieces of matter, and they'd annihilate each other in a big flash
But we don't see those flashes
But why didn't the universe start out with equal amounts of matter and antimatter that then annihilated each other, with nothing left over?
There are a lot of possibilities, and some of them have to do with our old friends, Neutrinos
You remember how Neutrinos are so weirdly light?
If there are also incredibly heavy Neutrinos, they would balance out the light Neutrinos by creating a whole family that kind of averages out at a more reasonable mass
these heavy neutrinos would have been
around just after the Big Bang when they
would have decayed into smaller lighter
particles and in the process produced
slightly more matter particles than
antimatter particles so if heavy
neutrinos did actually exists that could
help solve two mysteries at want first
it might explain why neutrinos have such
tiny masses and second it would explain
why this matter all over the universe
instead of antimatter it would be such a
nice elegant solution the only problem
is none of our experiments have found
evidence for it let's zoom way out now
from subatomic particles to whole galaxy
since gravity comes from mass
astronomers can use the amount
matter they detect in the galaxy to
calculate how strong it's gravity should
be but they've known for almost a
century that they must be missing
something stars orbit the center of
galaxies so fast that the galaxies
calculated gravity shouldn't be strong
enough to hold onto these stars should
escape into intergalactic space but they
don't
there must be some extra source of
gravity out there holding galaxies
together
astronomers call this source dark matter
and unlike antimatter we have no idea
what dark matter is made of all they
really know is that dark matter
interacts with regular matter through
the gravitational force and then it
seems invisible to telescopes also it
makes up about eighty-five percent of
the matter in the universe now there is
a much simpler possibility what if
astronomers are just wrong about the
laws of gravity maybe if they found the
right laws they could explain everything
without needing dark matter what dark
matter just explains too many things to
well from the way that galaxies are
distributed in a large-scale to the way
that matter clump together just after
the Big Bang plus astronomers have
actually found pockets of dark matter
that are completely separated from any
visible matter in other words they've
seen gravitational effects that should
be caused by matter in places where
there's no detectable matter even
changing the laws of gravity wouldn't
explain that so dark matter definitely
exists we just don't know what it is but
we do know what it isn't for example
lots of people used to think that dark
matter was probably just a lot of really
dim ordinary matter like small failed
stars called brown dwarfs or even
neutrino experiments have ruled out a
lot of those sorts of options there are
still plenty of other ideas out there
waiting in the wings for upcoming
experiments but for now
eighty-five percent of the matter of the
universe remains completely unexplained
there's also something weird about
matter itself starting about a second
after the Big Bang and lasting for about
three minutes protons and neutrons came
together in the first-ever atomic
nuclear physicists can use what they
know about particle physics and the
early universe to predict how much of
each element should have formed this way
hydrogen for example has just a single
proton its nucleus and because it's so
simple
about seventy percent of the atoms in
the universe should be hydrogen and
that's exactly what astronomers see when
they look at old star that same model
also predicts that protons and neutrons
should have come together to form helium
about twenty-seven percent of the time
so twenty-seven percent of the atoms
should have been Healy again exactly
what astronomers see when they check and
just about every element they look at
matches in the same way and then there's
lithia one form of lithium called
lithium-7 has three protons and for
Neutron and astronomers see four times
less of it than the model predict this
huge difference makes them think there
must be something wrong with either the
model over the measurements or both
astronomers make a few assumptions about
the early universe in order to predict
how much of each element was produced
and to measure how much of each of those
elements is actually out there they use
the light from stars were again they
have to make some assumptions about
things like the Stars temperature and
stability they could try to change some
of those assumptions to fit lithium but
there's a problem
these assumptions works so well for the
other elements that tweaking them to fit
lithium screws everything else up so a
lot of physicists think the lithium
problem means that there's some part of
physics that we're missing like the idea
of supersymmetry which says that every
particle has a kind of twin sibling with
a much larger map there's another idea
that the things we think are constants
of nature and basically set in stone
aren't actually constant if
supersymmetry is real that would mean
there were more particles in the early
universe and if the things we think are
set in stone actually aren't that would
change how the particles interactive so
both could help explain the weird
lithium numbers if we ever find evidence
for them but so far we haven't found in
the cosmic microwave background or CMB
is the oldest light in the universe is
often represented as a pattern of reds
and blues which show the different
densities of matter that eventually led
to big structures like our galaxy the
CMB was a really important discovery in
the 1960s because it helped confirm the
big bang theory it also hides an axis of
evil and yes that's actually what
scientists call it the axis of evil see
researchers expect that matter in the
early universe shouldn't have been
bunched up too much in any one place or
direction but that's not what they see
in the CMB instead they see a kind of
split between a more dense half and a
less dense half with an axis of evil
between the two and when they try to
divide up the CMB and other more
complicated ways than just seeing which
half is denser the axis of evil is still
there at first astronomers thought there
must have been something wrong with the
measurements or maybe but there was
something like a nearby dust cloud that
was messing things up but they've
checked and checked and checked and they
can't get rid of this axis make things
even weirder the axis of evil lines up
with the plane of our solar system we
point right at it and that's just
bizarre
astronomy is guided by something called
the Copernicus
principle which says there's no reason
our place in the universe should be
special but lining up with a
cosmological axis that formed billions
of years before earth did seems like it
puts us in a pretty special place now
it's completely possible that there's
nothing weird about the alignment always
probably about a 1 in 1,000 chance that
the conventional Big Bang model would
produce a universe with matter bunched
up like it is in the CMB those odds
aren't too bad and with trillions of
planets orbiting trillions of stars
throughout the universe
someone was bound to line up with the
axis of evil so maybe we just got lucky
and besides the alignment isn't perfect
it's just surprisingly good but
scientists still want to know why this
axis exists and whether there's a reason
our solar system lines up with
unfortunately they haven't come up with
my none of these mysteries will be easy
to solve but there are lots of smart
people working on all of them and
sometimes even on two or more once maybe
someday soon I'll be telling you about
the solutions to some of these problems
but in the meantime they'll keep
reminding us that there's still a lot we
don't know about the universe thanks for
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for example are thought to be a thousand
times higher with humans around then
they would be without but not all
endangered species are headed the way of
the dodo