Does Dark Matter BREAK Physics? | Space Time | PBS Digital Studios

Does Dark Matter BREAK Physics? | Space Time | PBS Digital Studios

[MUSIC PLAYING] Dark matter literally
binds the galaxy together. But there’s a problem. Nobody knows what
dark matter is. My name is Matt and
this is “SpaceTime.” Physics has a problem. The Milky Way galaxy
is spinning so fast that it should be scattering
its stars into the void. Based on the amount
of binding gravity that we calculate from
everything we can see, we can only account for
10% of the mass needed to hold its stars in orbit. So what’s wrong? Either we’re missing and frankly
don’t understand at least 80% of all the matter
in the universe or our current understanding
of gravity is wrong. This is the mystery
of dark matter. Now, before we get into figuring
out exactly what dark matter is or isn’t, I want to give you
completely independent evidence for its existence,
gravitational lensing. Thanks to general
relativity, we know that light fall is
the curved geodesics of a gravitational field. Place a strong
gravitational field on an axis between a light
source and an observer and voila, you
basically have a lens. And galaxy clusters
do this all the time, turning the background
universe into a funhouse mirror of stretched out and
duplicated galaxies. From this, we can figure out
exactly how much mass is needed to cause the observed lensing. But again, we find
the clusters appear to have way more mass
than we see in the stars alone, that is if we
understand gravity. So knowing this, let’s summarize
the actual possibilities for dark matter. One, best case scenario,
it comes from particles that we’ve already discovered,
just in a form that’s very difficult to detect. Two, not so great, dark
matter is a type of particle that’s beyond our current
understanding of particle physics. Or three, even worse, we’re
actually not missing any mass. Gravity just behaves
differently on the vast scales of galaxies and clusters. So general relativity, wrong. OK, let’s start with
the first possibility. The standard model
of particle physics is basically the periodic table
of known fundamental particles and fields. It underpins everything we know
about the subatomic universe. If dark matter
exists in this model, its mass probably needs to
come from protons and neutrons. But they can’t be
interacting with light. If this is dark
matter, the galaxy would need to be swarming
with baryonic things as massive as stars,
but that are so compacted that they’re
basically invisible. Is this even possible? Actually, it is. They’re called MACHOs,
massive compact halo objects. And they’re basically
crunched down, compact, dead or failed stars,
black holes, neutron stars, brown dwarfs, Macaulay
Culkin, et cetera. And they are very hard to see. But we can see these
guys, at least sort of, with gravitational lensing. The alignment has to be perfect. But when, say, a black hole
passes between us and a more distant star, we sometimes see
a brightening of that star. Astronomers spent years
counting MACHOs this way. And they found plenty. But not nearly enough to account
for all of the dark matter. So option one is out,
which means we’re left with two bad choices. Either particle physics
is wrong, or at least horribly incomplete, in that
we’re missing 80% to 90% of the mass in the universe,
or Einstein is wrong. Sacrilege, right? Remember when I said that the
Milky Way spinning too fast? Well, the problem is that the
stars on the edge of the galaxy are moving just as fast as
the stars near the center. But they should be moving slower
because the gravity out there should be weaker. According to Newton,
gravity weakens proportional to distance
from its source squared. This relationship is
definitely true on the scale of the solar system. But what about
the entire galaxy? Could it be that what we
see as dark matter just comes from gravity
behaving differently on truly gigantic scales? Well, it turns out that if
you make a simple change to Newton’s gravity,
things work out. Give gravity a bit more
staying power, make it drop off proportional to distance
instead of distance squared, and then you don’t
even need dark matter. The stars alone give
you plenty of gravity. The original modified
Newtonian dynamics hypothesis, and its general relativity
extensions, tries to give us this basic relationship
for gravity. 1 over R squared at small
scales, 1 over R at large. But you can’t just break general
relativity and start over. Any replacement theory
has to reproduce all, and I mean all, of the
verified predictions of Einstein’s theory and be
able to explain dark matter. Modified versions
of GR can actually do pretty well, especially
predicting orbits within galaxies. But they ultimately
have a hard time getting all of the observed effects. They either need some
serious fine-tuning or you have to add back
in some actual dark matter particles, which kind
of defeats the purpose. But there’s an even
bigger nail in the coffin of modified gravity. Say hello to the Bullet Cluster. It’s actually two clusters
that smashed right through each other. The gas was ripped
away from the stars and now lives
between the clusters. In the Bullet Cluster,
most of the mass actually is in the gas. So if dark matter really comes
from weirdly behaving gravity, then the cluster’s gravity
should stay concentrated on the gas. But if dark matter is
an unseen particle, and it’s the type of particle
we think it might be, then that dark matter should
pass right on through, just like the stars. How do we test this? Again, gravitational lensing. Map the mass based on
the warping of light from more distant galaxies. And we see that in
the Bullet Cluster, the dark matter
is with the stars. This tells us that matter
is a real particle, not just broken gravity. Once again, Einstein prevails. Dark matter exists and it
represents, if not broken, at least incomplete
particle physics. But what do we know about it? Well, it’s slow and it’s heavy. And those two go together. It has to be pretty
slow moving, or cold, because we know that dark matter
clumps together gravitationally to build galaxies and clusters. Remember the hot,
smooth plasma way back in the early universe
that produced the CMB? And the last guy
talks about it here. Well, in order to go from
that highly smooth ocean of orange plasma to today’s
highly structured universe of clusters and
galaxies, something had to act with enough gravity
to pull stuff together. There’s no way there’s enough
regular matter to do that. Dark matter, as well as
binding the galaxy together, is also the main force
in forming galaxies in the first place. No dark matter, no galaxies. And even then,
galaxies could only have formed if dark matter
particles are cold, massive, and weakly interacting. Weakly interacting
massive particles, WIMPs, actually refers to a specific
and popular contender for dark matter. WIMPs are a family
of particles that may arise out of supersymmetry. This is a funky extension
to the standard model of particle physics. Now, there’s a lot
to supersymmetry. But, in short,
versions of this theory predict the existence
of a set of counterparts to the familiar standard
model particles, but that are hundreds
of times more massive. Some of them fit the
bill for dark matter. Sinking down into the depths
of quantum field and string theory, you can find all sorts
of strange fish, WIMPs, axions, neutralinos. Some of which may actually
exist and some of them may be dark matter. But it’s all
mathematical fantasy until we detect the particle. We have detectors
here on Earth designed to catch the fall-out between
the unthinkably rare collisions between a dark matter particle
and an atomic nucleus. We also watch the heavens
for the equally elusive gamma radiation produced when dark
matter particles annihilate each other out in space. There’s a big fat
Nobel Prize waiting for the scientists who
figure this one out. So get cracking in
the comments below. And I’ll report any previously
undiscovered dark matter particles on the next
episode of “SpaceTime.” Last time on “SpaceTime,”
we talked about black holes. And you guys asked some
seriously challenging questions. Let’s see what you had to say. SafetySkull and others asked
whether a monkey falling through a black
hole’s event horizon should see the entire future
history of the universe happen in the instant
before it crosses over? The answer, no. But it would see some of it. If the monkey were to
calculate the clock time of an external
observer as it fell, then that calculated time
would approach infinity as the monkey drew extremely
close to the event horizon. That lasts an infinitesimal
fraction of a second before it crosses. It would encompass
all future time. But would the monkey witness it? No. The time interval
that encompasses all future everything
approaches zero, or at least the Planck time. So it’s not really happening
over a meaningful portion of the monkey’s in-fall. And anyway, the photons
from the future universe will never catch
up to the monkey because that light
has to contend with the same
crazy-curved space-time that the monkey does. Although signals from the
monkey to the outside universe can be received at arbitrarily
distance times in the future, only signals within its past
light cone can catch up to it. The monkey may see some
time dilation effects from the local part
of its universe. But it’s limited. Agen0000, and
others, pointed out that Hawking radiation will
eventually cause a black hole to evaporate. Given that a free-falling
monkey is eternally frozen on the event horizon with
respect to a distant observer, shouldn’t the black hole
evaporate beneath it? And would this save the monkey;s
life or fry it in an eternity of Hawking radiation? Again, the answer is no. The simple and unsatisfying
way to put this is that the free-falling
monkey doesn’t see anything weird about
space at the moment it crosses the event horizon. The space itself is in
free fall with the monkey. And so in its reference frame,
the rate of Hawking radiation is not time dilated. The idea of the event horizon as
this boiling hot sea of Hawking radiation isn’t right. In fact, in the vicinity
of the black hole, this radiation is
poorly localized, having a wavelength of order
of the Schwarzschild radius. So at the instant of
crossing the event horizon, the monkey is not actually
bathing in this stuff. But is the monkey saved at the
last moment as the black hole evaporates way beneath it? Sorry, no. By falling through
the event horizon, the monkey’s clock,
its universe, now contains events that happen
at the horizon, including the horizon’s existence. The monkey’s horizon crossing
corresponds to a time when the black hole exists. The distant observer
does witness the instance that the
black hole evaporates, with a huge burst of
Hawking radiation. And with that radiation comes
all of the remaining photons that the monkey emitted
before crossing the horizon. But the moment of horizon
crossing is never seen. It never even happens in the
distant observer’s universe, either before or after the
black hole’s evaporation. These were really
good questions. Keep them coming. And I’ll see you next time. [MUSIC PLAYING]


100 thoughts on “Does Dark Matter BREAK Physics? | Space Time | PBS Digital Studios”

  • I think dark matter is made of "matter" that doesn't interact normally, just at high scales and it can form a universe of it's own. That would require that the twos form a all, a twin universe. But I think it pushes, contrary to ordinary matter, so, the geometrical form would be like if matter was the holes in bread, if you want and the twin universe of "dark matter" the bread itself, but imagine, they interact like the bread was pushing in reverse with gravity, the "holes" of matter (it's just an image for the form it takes, don't imagine a hole, it's matter, our regular matter).
    It's not even my theory, it's the Janus cosmological model.
    I can't explain what I really mean…
    The two anti-universes maintain each other in the correct form we observe, we just can't observe the anti-universe directly, because when you invert a particle into it's anti particle, it annihilates. But if antimatter would form it's own anti-universe, maybe they were separated by some form of membrane at the big bang. That would explain why it "disappeared" since it should be in exact same quantity as matter, the difference was only invented because we can't find it or traces of it's existence (if they are in the same "space-time, kaboom!).
    Well, I tried to explain what I think, but it's hard, it's not even my primary language.

  • magnets only atract from a certain distance , then the attraction seams rapid . if two equal sized magnets attract, would they touch at the same speed as a small and large magnet at equal distance?
    if gravity acts in the same way, if the moon was to fall into the earth in a vacume would it fall at the same speed as a bus?

    if the force of attraction only starts at x distance before the gravitational acceleration and the pull of gravity starts relative to its volume, maybe dark matter doesn't need to exist .

  • Mandirigmang Pangkaragatan says:

    So this means that big guy Sagittarius A* at the centre of Milky Way is not enough to hold all stars of the galaxy in shape. Supermassive at it may seem, it is miniscule in mass compared to this Dark Matter.

  • Robert Wilkes says:

    I am very math-challenged, so I may be way off-base. But I heard Prof. Michio Kaku discussing String Theory and dimensions. Prof. Kaku said that his math works beautifully with 11 dimensions of reality. Working under the assumption that Prof. Kaku is correct, and there are 11 dimensions, even though we can only perceive 3 visually, and experience the 4th linearly, then it seems to me that dark matter is simply matter existing in dimensions 5-11 that we simply cannot perceive with our 3d minds.

    Does this make any sense?

  • If gravitational waves exist, would the positive side of the wave act opposite the negative side of the wave? like how positive and negative voltages react the same but opposite. would the positive end of the wave 'pull' while the negative end of wave 'pushed'? could the wave show its self positively as gravity and negatively as dark matter? maybe the combined effect of both is what we call inertia?

  • You've perhaps been in cartoonland much long time. Is air clear matter? Milky Way looks absolutely still from my house, how fast is it supposed to be spinning? LMAO

  • Dark matter does not exist. Gravitational lensing is not indicative of dark matter it's caused by light bending due to magnetic fields

  • Moe Larry The Cheese says:

    Matt why do we call it matter? we can see matter. its an invisible field. why do you never speak of the invisible arms of force and why doesn't anyone ever talk about how stars must have invisible arms of force that keep the planets swirling? Really Please! or does physics need me for some problem solving?

  • Danny Garcia says:

    Dark matter kinda acts like our air in our atmosphere, except being it isnt bound to a single direction it pushes and pulls depending where its concentrated, more dark matter in a given area, the more mass it moves, the less dark matter, the more the mass is pulled , idk just said write you thoughts in the comments

  • I know what dark matter is, and you can keep making videos that keeps asking the same question. Everything you know is wrong. And yes Einstein was wrong and every scientist is wrong. Neil T. Degrasse is wrong. The dude in the wheelchair was wrong.

  • Just a suggestion off the top of my head – could the dark matter problem be fixed simply by the use of string theory?

  • Dark matter is an error based excogitation:
    More interesting documents at:

  • William Crownin says:

    Dark matter is the force.

    "Life creates it, makes it grow. Its energy surrounds us and binds us.

    "You must feel the Force around you; here, between you, me, the tree, the rock, everywhere, yes. Even between the land and the ship."


  • How about theory #4. We just haven't taken into account the oort cloud type galatic debris, and dwarf planet sized orbital remnants, in distant star systems.

  • Reggie Anderson says:

    Wrong no MACHOS they don’t objects don’t have objects revolving around tiny points . Gravity is missing something.

  • A normal conversation

  • would the integer spin of bosons and the half integer spin of the up quark and down quark indicate a full bridge rectified DC system? resource


    Dark Energy was so compressed and dense at the time of the big bang, that it would be like a dense black hole exploding. As it exploded it continues to expand. It's not that more space is created to 'fill the gaps', the space was always there but slowly becoming less denser – we just cant pick up the miniscule calculation of the density change yet with our current computing methods. This means as the universe is constantly expanding and increasing in speed, that dark energy is causing it to expand and has billions upon billions of years of expansion yet to go. To what end do our best calculation computers go to? Not enough yet to detect and measure just how much density dark energy changes and has yet to release. RS. Australia.

  • What about if dark matter is in extra dimension that is orthogonal to our spacetime continuum, as suggested in the following article?

  • Well I mean " black lives matter" breaks white ethics so why not? notice the discrimination in exclusive racial bias to join..

  • Another possible canidate for dark matter; is matter existing in a near by parrallel universe; dark mattee could exist in another dimention were its gravity has an effect in our universe; in string theory gravitt can leak into other dimentions; the graviton particle could exit into our dimention which can cause the gravitational distortion of light in our universe; which why gravitstional lensing can be used to detect the dark matter in galaxies.

  • Why can't the dark matter simply be regular matter in lumps to small to observe with our current technology. How many rogue planets and asteroids and failed stars aka brown dwarfs and fist sized lumps are floating around out there around what we can see both inside the visible galaxy and outside in a halo? Wouldn't that produce the same effect as some mythical "dark matter"?

  • Just like you said the outer stars of galaxy should move slower but it isn't, so could it be possible that this zero relative velocities of interior and exterior stars of galaxy is due to the gravitational effect of other stars close to the exterior star which causes it to move at the same velocity as they are and same also happens to them( like a chain effect).

  • Let 's make it simple, dark matter work as sea water and the galaxies work as a ships, and the dark matter inside galaxies work as sea water with less density so it keeps the stars inside itself,

  • Nehmo Sergheyev says:

    I realize I'm writing 3 years after this video's upload, and I have the advantage of current research (and opinion), but I don't see what's so dumbfounding about dark matter. The Bullet cluster should convince anybody. It's here, and it's part of the big story. There's no reason to be amazed and shocked by just another part of physics.

  • Julian Klappenbach says:

    What could dark matter be?

    I think you forgot something?

    1. Best Case Scenario: small, stellar mass black holes, at the required density to generate the effects we see, with a relatively smooth distribution so there's no clumping. If there were inconsistencies in the distribution of matter in the initial moments after the big bang, it's very reasonable to assume a full distribution of densities in that irregularity. Thus we should have a wide variety of singularities included in that distribution. Sizes would have ranged from the ultra small (which may have given us wimps), to perhaps the seeds that gave us the initial galaxies. The smallest would have decayed fairly quickly due to Hawking radiation. Others, in the stellar mass range, should still be around now. And if we have a bell-curve for size distribution, I'm betting that the stellar mass variety had the highest population.

    To me, this makes much, much, much more sense than inventing exotic particle physics or altering the well established, locally observed relativistic behavior of gravity for something that was scale dependent.

    Also, I believe there is one effect that we all have completely left out: relativistic frame dragging. Galactic core singularities have an upper bound of billions of solar masses, and as they rotate, I would expect them to have a frame-dragging influence that would alter space-time over the span of thousands (or more) of lightyears.

    If you have difficult time understanding, picture this: most black holes are spinning. As they spin, they not only warp spacetime by collapsing it, they spin space-time around with them. Stars, therefore, would not just be orbiting around the singularity, the very fabric of space-time they exist on would be moving as well, resulting in a higher than expected total rotational velocity. The effect has been measured on satellites orbiting around earth, though the effect scales with mass. So, on earth it is relatively small. Still, it's large enough to create a difference of tends of feet a year. Imagine what a billion solar mass singularity could do to the volume of a galaxy. Have these two combined scenarios been considered?

  • Nicola Cappellini says:

    "Clocks approaching infinity! Calculator events on edge of the horizon! Monkeys!" Without the context of the previous episode, the words at 8:03 – 8:54 sound like random gibberish of a rambling lunatic…

  • John C Gibson says:

    Just read today's Forbe magzine's article about using dark matter as propellant and as fuel for interstellar traveling. Very exciting time for physics.

  • Jacob Bøge Andersen says:

    With no discernible fear of parallel development of my cheap and tasty thesis, as it seems so profound, that it must be a one off:

    If PBS is an abbreviation of peanut butter sandwich, then; supposing that PBS, at some point in the future merges with other entities to form "PBJS", then I submit to you, my poor and suffering audience, that jelly is to PBS, as dark matter is to space time, for that matter, or mayhap not, though likely not in so many words. [dancing banana]

  • What if neutrinos actually have mass, it is just so small that we can't yet measure it, would that account for dark matter?

  • Isn't Dark Matter gravity itself? Like elcetromagnetism is based on a particle exchange of massless quanta, couldn't Dark Matter be the elusive graviton being exchanged between quanta that exhibit a mass effect? It could partially explain the colossal disparity between the size of electromagnetic force and gravitaional force. If most of the mass of astronomical bodies is in transit between them could it not generate a self-cancelling effect based on some funky spin dynamics? I dunno, just spitballing

  • Maybe dark matter is just normal matter in a parallel universe, which is close enough to ours in the 4th dimension that it affects ours gravitationally.

  • You said scientist counted the stars on the milky way to derive the mass. Did they counted black holes aswell? After all, there is nothing more dark than a black hole and they are massif!

  • I am sure everyone from the last 5 centuries of great minds, are most likely going to be fully proven wrong or partially. Answers soon to come about everything and why it's here and how it all works will truly be beautiful. Religious people stay away from this comment-.-


  • Why doesn't dark matter affect things on the scale of the solar system or even smaller – like on earth? Perhaps dark matter is not a particle, but instead some un-thought-of state of existence.

  • I do worry about this almost religious orthodoxy around Einstein's theories. They'll probably turn out to be wrong just as Newton's were. Doesn't mean they weren't an important stepping stone.

  • Michael Thomas says:

    ALL BULLSHIT. You don't even know WHAT GRAVITY IS!!! You so called scientist just think gravity is a force, AND YOU CAN'T EVEN PROVE IT EXIST!!!. You use formulas which mean crap to try to explain stuff, but often your formulas PROVE to be junk. You just make crap up out of guess work, while trying to make it real to us with CGI demonstrations. Screw off

  • Isn't dark matter the membrane barrier of matter particles that cocoon our energy conserving galaxy within the infinite free flow of dark energy particles that make up 70% of the known universe?
    A galaxy's gravity limits the free flow of dark energy particles within it's membrane to sublightspeeds or, the speed of gravity of the galaxys black hole and singularity. Matter and entropy are the evolution of low energy particles within a galaxy's thermodynamic, gravity field.

  • Daryl Nicoloso says:

    How much matter exists in inter stellar space between stars? It is a massive expanse light years wide. Could the missing mass be there as invisible hydrogen and other lite elements?

  • Dave Kachorowski says:

    Other fields, besides gravity, start in short distances as 1/r^3, the 1/r^2 then 1/r. So why can't gravity behave this way????

  • Dark matter is an invisible particle known as gluon. This means that matter is composed of more than 99,9% of dark matter. In fact, what we see as matter is photon reflexion on dark matter dense packs, gluons by billions known for holding together quarks. Can I prove this. Yes, but not with "quantum Physics". RCP

  • …if Dark matter reflect no black body radiation at all, why to presume
    that something is there. It is a hole in the SpaceTime field, no energy
    no time. We live in a cheese like Universe. Thank me later.
    more possible it is SpaceTime contouring, bending all around the hole
    creating a lensing effect, not gravity but a hole. A hole in SpaceTime,
    nothing inside, no Energy nor Time, like bubbles of nothing. Maybe? Have
    we experienced anything bouncing off of Dark Matter? Have anything flew
    thru Dark Matter? Have we witness any celestial buddy or radiation
    pulled towards Dark Matter gravitation? Not gravity, just SpaceTime
    ruptures, stretched, teared apart after loosing energy, holes of…
    Ups, here goes nothing. Galaxy rotation and everything else… SpaceTime
    "Field Tensors" Get it? Einstein got it right, a Universal constant, all along

  • It seems to be that all stars in a galaxy interact with each other, causing the summing of their own gravity pull, affecting it all?
    One star attracts nearby stars, and it's attracted to them also, all in equilibrium, and the sum of each one makes up for the enormous amount of gravity of the galaxy. I see galaxies not as one thing, but a group of things. A group of stars arranged in a pattern due to the trading off, of multiple angular momentum? That could be the reason of stars keep synched in place & velocity of rotation of the total structure (galaxy).

    Maybe gravity is not a force but a quality that changes behavior at greater & grater scales? Superclusters don't behave the same as clusters, and clusters to galaxies, and galaxies to star systems. Could be that there's a limit, a simil ''Schwarzchild limit'', but for great structures?

    Clusters are arranged more linear, and superclusters more as a net. Maybe there's one more step, and there's a greater structure than the big net of superclusters, where gravity behaves totally (or arranges matter) different
    I'm not a physic's student, but have a friend that is a professor in Physics and he shared me invaluable knowledge in our talks.

    Loving this channel more and more!! 🖤

  • YOU ARE 100% bullshitters !!! By the way , why do you show a picture of Einstein when you say gravity !!! STUPID MOTHERFUCKERS !!! FUCKING IDIOTS !!! Don't you know that was Isaac Newton the one that was discovering gravity ???? fucking U.S. dummies !!! ASSHOLES !!! I unsubscribe now !!! fucking crappers !!!

  • What will happen to monkey, I literally have no idea what he just said. I could only understand one sentence " monkey will die and won't see any future"

  • Wow. Matt from 4 years ago looks like he stayed up all night and discovered something important. Now he has a more calm confidence. I think that is evidence he loves his job.

  • vidhuresh boganathan says:

    Plz notice,

    Hey why can't the quantum field fluctuation and fluctuation tunnels provide enough mass in the form of energy?🤔🤨🧐

  • There is no need for dark matter when you balance the equation of gravitational displacement (downward in 3d representation) with pressure (Upward) both add to hold a galaxy together. Mass Pulls, and the balance repulsive force around the galaxy pushes. Imagine an above ground swimming pool covered in a sheet of spandex and you place a cannon ball in the center. THAT is conventional dark matter representation…. now replace the spandex w rubber sheet that is impermiable, where what is displaced has to be accounted for in an upward fashion around the edges, and welcome to understanding how space/time actually works… no need for dark anything.

  • Why do we not just apply Occam's Razor and conclude the simplest explanation? Newton's Laws do not apply on cosmic scales.

  • Christopher Avery says:

    Imagine a substance you can't fathom. Then imagine a deity placing stars and matter into it. With home being placed last. I don't know but that's what it seems. It's almost fictional

  • I wonder if wormholes are caused by, something like a whirlpool, only in space? If you drop a leaf into a whirlpool in a body of water, it will be sucked down into the water at a very high speed to the bottom of the pool. If a star passed into the black hole it would be sucked in and pulled to the other end at a very rapped speed. It makes you wonder if you could space travel this way if one could create an artificial vacuum, like a whirlpool in space.

  • I learned two things from this video: 1) Even though Einstein can't possibly be completely right, he always wins in the end, and 2) Space used to be orange.

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