welcome back my friends so before we get into the curse because act video as i do in every video
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yeah come get involved anyway let's get into the video alrighty what is dark matter and dark energy
matter as we know it atoms stars and galaxies planets and trees rocks and us
this matter accounts for less than five percent of the known universe
about 25 percent is dark matter and 70 percent dark energy both of which
are invisible this is kind of strange because it suggests that everything we experience
is really only a tiny fraction of reality but it gets worse we really have no clue what dark
matter and energy are or how they work we are pretty sure they exist though so what do we know
dark matter is the stuff that makes it possible for galaxies to exist when we calculated why the
universe is structured the way it is it quickly became clear that there's just not enough normal
matter the gravity of the visible matter is not strong enough to form galaxies and complex
structures stars would more likely be scattered all over the place and not form galaxies so we
know there is something else inside and around them something that doesn't emit
or reflect light something dark but besides being able to calculate the existence of dark matter
we can see it kind of places with a high concentration of dark matter
bend light passing nearby so we know there's something there that interacts with gravity
right now we have more ideas about what dark energy is not than what it is we know
dark matter is not just clouds of normal matter without stars because it would emit particles we
could detect dark matter is not antimatter because antimatter produces unique gamma rays when it
reacts with normal matter dark matter is also not made up of black holes very compact objects that
violently affect their surroundings while dark matter seems to be scattered all over the place
basically we only know three things for sure one something is out there two it
interacts so that first one i have a problem with because that is not something we know for sure
dark matter might not actually exist uh we just might be looking at things in the wrong way you
might have heard of modified newtonian dynamics and things like that so there really is the
possibility that dark matter just doesn't exist and we're looking at things you know very badly
dark matter is probably made up of a complicated exotic particle that doesn't interact with light
and matter in a way we expect but right now we just don't know dark energy is even more
strange and mysterious we can't detect it we can't measure it and we can't taste it but we do see
its effects very clearly so basically we call it dark energy because the term we have to introduce
in the famous you know einstein's field equation for general relativity has units
of energy in 1929 edwin hubble examined how the wavelength of light emitted by distant galaxies
shifts towards the red end of the electromagnetic spectrum as it travels through space edwin hubble
actually restores my faith in humanity a little bit because he started out a lawyer
became an astronomer he found that fainter more distant galaxies showed a large degree of redshift
closer galaxies not so much hubble determined that this was because the universe itself is expanding
the redshift occurs because the wavelengths of light are stretched as the universe expands
so what he basically saw was everywhere he looked at every single galaxy it was basically they
were basically all moving away from us and the further away he looked the faster it was moving
away from us so think about this all around you everywhere you can see galaxies are moving away
further away they're moving faster so that kind of suggests this thing is expanding right recent
discoveries have shown that the expansion of the universe is accelerating so that recent uh thing
that showed us it's actually exhilarating was using our uh white dwarfs and supernova explosions
and we can use this as kind of like a standard candle we call it the distance measurements
and we basically found that you know it's accelerating the further you look back
you know you can you can imagine how you could just detect this by you know using a
measurement and then further where you know how much it should be so you can look at this
and realize you know this this dark energy is actually making the universe expand quicker
it was thought that the pull of gravity would cause the expansion to either slow down or even
retract and collapse in on itself at some point space doesn't change its properties as it expands
so this stuff dark energy actually has uh negative pressure we think and this means that gravity
behaves as though it's like repulsive and so like a crude you know not really appropriate analogy is
like a bubble in the sea rising because of gravity uh and so as a result dark energy basically
has this interesting property where its density remains constant even as it expands right and so
here's the way it works when gravity acts on stuff with positive pressure it compresses it right you
know self gravity compresses a cloud of gas into a much more compact object aks style and so the work
done by gravity appears as increased pressure and temperature but when gravity does work on stuff
with negative pressure like dark energy it causes it to expand right and the work done by gravity
uh in the case of dark energy it produces more dark energy and so the density of dark energy
doesn't decrease even in an expanding universe and so there you have it you know we start with
an expanding universe with lots of matter and a little bit of dark energy um and at first the
expansion keeps slowing down because of gravity and but you know as time goes on the density of
matter keeps decreasing whereas the density of dark energies just doesn't so eventually you
reach a point where the density of matter falls below that of dark energy and from that point on
the repulsive behavior of dark energy basically dominates and so instead of slowing down
uh gravity accelerates expansion and so in our 13.8 billion year old universe
this turning point happened roughly between like four to five billion years ago more of it
new space is constantly created everywhere galaxies are tight bound clusters of stuff
held together by gravity so we don't experience this expansion in our daily lives but we see
it everywhere around us wherever there is empty space in the universe more is forming every second
so this dark energy looks like it's a very very weak thing because you know where we
see baryonic matter typical matter gravity seems to be way stronger and you know it
pulls stuff together but over large distant scales it seems like this dark energy takes
over and it's kind of like an opposite gravity it looks like it's it's pushing things away
um so what he's saying here is kind of incorrect we don't know if that's happening um it could be
so i'm bringing this up because people think you know like here where we're walking around there's
new space emerging or something or the universe is getting stre expanding but
that's just not happening in regions where there's baryonic matter it looks like at least
so dark energy seems to be some kind of energy intrinsic to empty space
energy that is stronger than anything else we know and that keeps getting stronger as time passes by
empty space has more energy than everything else in the universe combined we have multiple ideas
about what dark energy might be one idea is that dark energy is not a thing but just a property of
space empty space is not nothing it has its own energy it can generate more space and is quite
active so as the universe expands it could be that just more and more space appears to fill the gaps
and this leads to a faster expanding universe this idea is close to an idea that einstein had back in
1917 of a concept of a cosmological constant a force that counteracted the force of gravity the
only problem is that when we tried to calculate the amount of this energy the result was so wrong
and weird that it only added to the confusion all right let me give you some of the you know leading
candidates for what dark energy could be but just remember that we really don't know what it is
so it could be a cosmological constant you know a constant of nature arguably like a fundamental
property of empty space right uh if it exists it could be vacuum or zero point energy of all
the the quantum fields of the standard model of particle physics and as such it would be like a
fundamental property of the vacuum empty space uh it could just be the self-interaction energy
of a like a yet to be discovered scalar field but you know chances are uh dark energy is something
else altogether and perhaps it doesn't even exist like you know maybe the data implying it
cosmic expansion is you know just a little bit misinterpreted we won't know until we know i
guess and so far you know attempts to detect it or discover it's you know true nature are pretty
hopeless just an fyi the vacuum energy would be a pretty ideal candidate but unfortunately the
predicted uh vacuum energy density is like 120 orders of magnitude too big resulting
in probably the greatest discrepancy between like theory and observations in the history of physics
the so-called uh cosmological constant problem a lot of people call this the most embarrassing
problem in physics another idea is that empty space is actually full of temporary virtual
particles that spontaneously and continually form from nothing and then disappear into nothing
this isn't something he should have put in here um virtual particles is uh virtual particles they're
not real that's why they're called virtual for one they're just like this calculational tool
we use in uh quantum field theory we don't actually think that's what's happening
um there's different ways to look at these things but it gets really complex because
um to describe fields in quantifiable theory takes you know some strange math
and it there's no analogy to a quantum field in you know with in our real world like i can't
tell you it's just like a wave because the quantum field is not like a wave um
so people just present this virtual particle thing because it's something you can imagine whereas
what's really happening is vastly different the energy from those particles could be dark energy
or maybe dark energy is an unknown kind of dynamic energy fluid or field which permeates the entire
universe but somehow has the opposite effect on the universe than normal energy and matter
but if it exists we don't know how and where or how we could detect it so there are still
a lot of questions to answer we don't know if laws of physics are even the same you know on
the other side of the universe these are things we're still figuring out recent studies have tried
to look at the fine structure constant which is kind of like the strength of electromagnetism you
know light uh you know the thing that's holding all atoms together essentially and stopping you
from falling through the floor and you know it's responsible for your brain working and essentially
everything right um we're trying to measure this fine structure constant which has this really
weird value by the way one over 137 extreme it's kind of the number you would use if you wanted
to communicate with aliens okay it's just this mysterious number at the bottom of physics that no
one understands um and fun little trivia fact in rick and morty c137 you know the universe that's
where they're getting this from and so we're trying to measure this uh fine structure constant
you know on the the edges of the as far as we can essentially okay so to see if it's the same to see
if the laws of physics is the same everywhere our theories about dark matter and dark energy
are still just that theories on the one hand this is kind of frustrating on the other hand this is
frontier science making it very exciting it shows us that no matter how much we feel we're on top of
things we're still very much apes with smartphones on a tiny fragile island in space looking into the
sky wondering how our universe works there is so much left to learn and that is awesome it's like
what einstein said you know the most beautiful thing we can experience is the mysterious and
what's more mysterious than dark energy and dark matter you know maybe consciousness but uh yeah
they're definitely up there so i feel like people generally uh want to hear more about what we do
know instead of what we don't know is i don't want to sit here in these videos the whole time saying
we don't know we don't know because you know with dark energy and dark matter we don't know
and dark energy is kind of just like a placeholder for something we have no idea about
but something we do know about dark energy is that it looks like it's the only thing in the universe
that can escape black holes that's right dark energy uh just you know black holes don't have
any impact on dark energy and this is basically because dark energy isn't affected by gravity
dark energy kind of you know acts in an opposing way we think anyway that will do for today's
video guys i don't want to talk too much about all this stuff we don't know you know we could
talk about all the different kinds of theories floating around and all the different ideas but
none of it is uh you know we just don't know so i don't want to talk for too long