NEIL DEGRASSE TYSON: When we think of places
you might find life we typically think of the Goldilocks Zone around the star where
water would be liquid in its natural state. And if you get a little too close to the star,
heat would evaporate the water and you don't have it anymore. It's gone. Too far away it would freeze and neither of
those states of H2O are useful to life as we know it. We need liquid water. So you can establish this Green Zone, this
habitable zone, this Goldilocks Zone, where if you find a planet orbiting there hey, good
chance it could have liquid water. Let's look there first for life as we know
it. Now it turns out that this source of heat,
of course is traceable to the sun and if you go farther out everything water should be
frozen, all other things being equal. But Europa, a moon of Jupiter sitting well
outside of the Goldilocks Zone is kept warm not from energy sources traceable to the Sun,
but from what we call the tidal forces of Jupiter itself. So, Jupiter and surrounding moons are actually
pumping energy into Europa. And how does it do that? As Europa orbits Jupiter its shape changes. It's not fundamentally different from tides
rising and falling on Earth. The shape of the water system of the Earth
is responding to tidal forces of the moon. And when you do that to a solid object, the
solid object is stressing. And because of this, a consequence of this
is that you are pumping energy into the object. It is no different from when you say to anyone
who's familiar with racquet sports, indoor racquet sports. It could be racquetball or squash. You say let's arm up the ball before we start
playing. You want to hit it around a few times. You are literally warming up the ball. It's not just simply let's get loose. You are literally warming up the ball. How? You are distorting it every time you smack
it and then the resilience of the ball pops it back into shape and every time you do that,
every smack, you're pumping energy into the ball. It's not fundamentally different from what's
going on in orbit around Jupiter. So, you have this frozen world, Europa, completely
frozen on its surface but you look at the surface and there are cracks in the ice. There are ridges in the ice where there's
a crack and it shifted and then refroze. So this ridge has a discontinuity in the crack
and it continues in another place. So what this tells you is that Europe cannot
be completely frozen because if it were nothing would be moving. You look at the surface of Europa, the frozen
surface, there are like ice chunks that are shifted and refrozen and shifted again. It looks just like if you fly over the Arctic
Ocean. Fly over the Arctic Ocean in the winter these
are ice sheets that are breaking and refreezing all the time. It's the same signature as that. So all of us are convinced that beneath this
icy surface is an ocean of liquid water. And there's no reason to think it wouldn't
have been liquid for billions of years. On Earth where we find liquid water we find
life. So what this means not only do we have a source
of heat outside of the Goldilocks Zone, we have conditions under which life could be
thriving. And knowing that this is possible has completely
broadened the net that we are casting in search for life in the universe. No longer is it the limit, let's find a 72
degree tidal pond and see life forming there. No, life is pretty hardy. And by the way Europa is not the only one
of these moons in the outer solar system that's kept warm by these sort of tidal stress forces. There are other moons that feel the same influx
of energy. So, for example, Io, that's the innermost
moon of Jupiter. That suffers from this phenomenon even more. And that moon is so hot there are volcanoes
erupting from within. It is rendered molten, whatever solid parts
of that moon there are. And so, in fact, the most volcanically active
place in the solar system is Io, one of the moons of Jupiter. And we don't know how to sustain life under
temperatures that hot so, but it's a reminder that if you're looking for sources of energy
we no longer need to be anchored to a host star in our search for life in the universe. The question isn't about whether dark matter
exists or not. What's going on is when we measure gravity
in the universe the collective gravity of the stars, the planets, the moons, the gas
clouds, the black holes, the whole galaxies. When we do this 85 percent has no known origin. So it's not a matter of whether dark matter
exists or not. It's a measurement, period. Now, dark matter is not even what we should
be calling it because that implies that it's matter. It implies we know something about it that
we actually don't. So a more precise labeling for it would be
dark gravity. Now, if I called it dark gravity are you going
to say does dark gravity really exist? I'd say yeah because 85 percent of the gravity
has no known origin. There it is. Let's figure out what's causing it. The fact that the word matter got into that
word is forcing people to say I have another idea. I bet it's not matter. It could be something else. We're overreacting to a label that overstates
our actual insights or knowledge into what it is we're describing. Then I just joke we should just call it Fred. Fred or Wilma, something where there is no
reference to what we think it is because, in fact, we have no idea. So here's how you actually measure the stuff. In a galaxy which is the smallest aggregation
of matter where dark matter manifests, so you look how fast it's rotating and we know
from laws of gravity first laid down by Johannes Kepler and then enhanced and given further
detail and deeper understanding by Isaac Newton. You write down these equations and say oh,
look how fast it's rotating. You invoke that rotation rate in the equation
and out the other side says how much gravity. How much mass should be there attracting you. And the more mass that's there the faster
we expect you to be orbiting. That kind of makes sense. So when you do this calculation on a galactic
scale we get vastly more mass attracting you than we actually can detect. I'm adding up stars, gas clouds, moons, planets,
black holes. Add it all up. It's a fraction of what we know is attracting
you in this orbit. And we cannot detect the rest. And so we hand it this title dark matter. Understandably I suppose but it implies that
we know that it's matter, but we don't. We know we can't detect it in any known way
and we know it has gravity. So it really should be called dark gravity. I think the over/under on what dark matter
might be today I think we're all kind of leaning towards a family of particles, subatomic particles
that have hardly any ability to interact with the particles we have come to know and love,
""ordinary matter."" And that would make it matter. Dark matter as we've all been describing it. And it's not a weird thing that you could
have a particle that doesn't interact with our particles. Within our own family of particles there are
examples where the interaction is very weak or nonexistent. You might have heard of neutrinos. This is a ghost-like particle that permeates
the universe and hardly interacts with familiar matter at all. Yet it is part of our family of particles
that we know exist and that we can detect and interact with. So if we can have an illusive particle that's
part of our own familiar family of particles it's not much of a stretch to think of a whole
other category of particles where none of them give a rat's ass about the rest of us
and they just pass right through us as though we're not even there. Now here's what's interesting about dark matter. We know it doesn't interact with us except
gravitationally. By the way what do I mean by interact? Does it bind and make atoms and molecules
and solid objects? No, it does not interact with us in any important
known way. But it also doesn't interact with itself. That's what's interesting. So, if it interacted with itself you can imagine
finding dark matter planets, dark matter galaxies because to interact with yourself is what
allows you to accumulate and have a concentration of matter in one place versus another. These are the atomic bonds and the molecular
bonds that create solid objects and if particles do not interact with one another they just
pass through, you just have this zone of mass not really doing anything interesting. So, dark matter not only doesn't interact
with us, it doesn't interact with itself. And that's why when we find dark matter across
the universe it's very diffusely spread out. It's like over here. It's not in this one spot and look at this
concentration. No, that's not how that works. Just as a quick example, I was channel surfing,
came across a football game that had just ended in a tie. They went into overtime. I had 15 minutes to kill before my movie came
on. I said I'll sit there and watch this overtime
period. And I'm watching it and there's the requisite
exchange of possession before you go into sudden death overtime. So, they get it to within 50 yards of the
goalpost and so they decide to kick a field goal for the win. And so I'm watching this and it's exciting,
right. So then the ball gets hiked, they kick, the
ball tumbles and it heads toward the left upright, careens off the left post and in
for the win. And I said wait a minute. Oh, we have a round ball and a cylindrical
thing so fractions of an inch matter which way this will bounce off of a post. So I said let me check this out. So I check the orientation of the stadium,
the latitude of the city and I did a calculation and then I tweeted and I said, ""The winning
field goal by the Cincinnati Bengals in overtime was likely enabled by a third of an inch drift
to the right, enabled by Earth's rotation."" And people say oh, my god. Blow my mind. And the local news got it and everybody got
it. Of course you want to know that the rotation
of the Earth helped that field goal kick. Because a kick going due north or due south
will be deflected to the right in the northern hemisphere. And that's exactly what happened to that kick. And I use that as an excuse to send out a
second tweet saying, ""By the way, we call this the Coriolis force and that's what creates
the circulation of all storms. Hurricanes, tornadoes."" What do they call them in the Pacific? Cyclones.
Earth's rotation is a Bengals fan, CONFIRMED.
I would like a scientific explanation for all those games we lost in crazy ways
Thomas Rawls ran all over them that game and then Dandy led that crazy comeback in the 4th to send it to OT. Can’t wait to see PBS rocking like that again