The science of expansion: Andromeda, gravity, and the ‘Big Rip’ | Michelle Thaller
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The science of expansion: Andromeda, gravity, and the ‘Big Rip’ | Michelle Thaller


One of the questions I get asked most commonly
as an astronomer is if almost all the galaxies in the universe are flying away from us in
space, why is the Andromeda Galaxy getting closer to us? Does that somehow mean that the Big Bang works
differently in different parts of the universe? And the answer simply is: no. Space is expanding because of the Big Bang. All of space is expanding in every direction
all at once and from our viewpoint that means that it looks like all the other galaxies
are moving away from us. But not all the universe around us appears
to be expanding. For example, the Earth doesn’t seem to be
getting any farther away from the Sun. The Sun is not getting any farther away from
our galaxy. Thank about smaller scales, like your body;
your body (luckily) is not expanding along with the universe. And the reason is that the expansion of the
universe is actually a pretty gentle force; you really only notice it out in the middle
of nowhere in the vast reaches of space between the galaxies. There’s a lot of space out of there, so there
is a lot of space to expand and so you really notice this expansion. But there are things that are stronger than
the expansion force. For example, my body is held together by chemical
forces and by electrical forces. That is much, much stronger than the tiny
little push that space has to expand inside me. I hold together very well. One of the analogies I think about is: You
could try to push over the Empire State Building by blowing on it. You are actually exerting a force on the Empire
State Building by blowing on it, you can measure that force, but you’re not going to blow over
the Empire State Building. There are things that are much stronger than
this omnipresent but gentle force of the expansion of the universe. The gravity between the Sun and the Earth
is stronger than space’s pressure to expand over that scale. The force of gravity is stronger than the
outward push of the expansion of the universe. That’s also true of the galaxy, we are held
in orbit around the center of the galaxy. Gravitationally, that’s much stronger than
any expansion force. So why is Andromeda different? Andromeda is close enough to our Milky Way
Galaxy that the gravity between the two is strong enough for the two to start moving
together. Yeah, space is expanding between us and the
Andromeda Galaxy, but gravity is accelerating Andromeda toward us faster than that expansion. And, in fact, that means that Andromeda is
going to collide with the Milky Way in a couple billion years. And we see this happening all over the universe. There are clusters of galaxies where the galaxies
are close enough together that they are merging and colliding. When galaxies are far enough away from each
other that the gravitational force is weaker, the acceleration due to gravity is weaker
than the outward expansion, then they start moving away. Now one of the intriguing things is that we
don’t know what the future holds when it comes to the expansion force of the universe. Just recently in the last couple of decades
we’ve measured that the universe is not only expanding but it’s actually accelerating. In some ways that force is getting stronger
and stronger all the time and we don’t know whether that will stop or whether that will
stay constant or whether in fact that expansion force will keep getting stronger. Will there be a day when the expansion force
of the universe is strong enough that our galaxy does start to expand and the stars
start to move farther and farther away from each other? Will there come a time when the Sun and the
Earth are actually pulled apart by the expansion of the universe? And perhaps most intriguingly, will there
ever come a time when the expansion of the universe is strong enough to rip apart your
atoms, to actually have matter disappear into a little soup of organic particles? We call this idea the Big Rip and it’s one
of the possible ends of the universe – that the expansion force will eventually get so
strong it literally rips everything apart. We don’t know whether this will happen yet
so we have a lot more investigating to do about this thing called dark energy that may
be accelerating the universe and that’s one of the best questions we’re trying to answer
right now.

77 thoughts on “The science of expansion: Andromeda, gravity, and the ‘Big Rip’ | Michelle Thaller

  1. Hi Michelle. My question is are you just another facet of scientism where your claims can’t be measured, or verified, or testable? Are you essentially a religious leader teaching so called science and when we question what you say we get called an idiot?

  2. I'm not an astrophysicist, so please bear with me. I can't help but think the inverse square law (as it applies to gravity) is playing a major role in the universe's expansion. For example, if gravity diminishes exponentially with distance, and vacuum pressure (i.e. dark energy) is constant, then expansion should accelerate. Or at least, it seems that way.

  3. Please provide a photograph of the earth that was taken from outer space. Has gravity been proven? Please provide the proof that gravity exists. Question everything, and research “operation paper clip”. We were all taught what to think. We were taught the sun is 93 million miles away. We were not allowed to question these statements of fact, thus we do not know how to think.

  4. The science classes of our public schools need to step it the fuck up!
    I started to really learn the methodology of science when I stopped going to class and started going to the library/book store. I failed science class because I was never there, but knew more about it than the damn teacher…

  5. Michelle says that it is an "expansion force," but is it a "force" that is pushing things outwards, or is it the geometry of spacetime itself that is growing larger?

  6. Big Think, could you please mention Michelle on the beginning of the title? When you mention her on the end, due to long title it can be cropped out. If I haven't seen her name in the thumbnail, I may not have clicked on this video.

  7. My understanding is that Andromeda is more massive than the Milky Way, so more accurately – Gravity is accelerating us toward them. (Technically each to each other, but we'd accelerate faster – if the forces are the same and the Milky Way is less massive, we should accelerate more rapidly.)

  8. She is so wonderful at explaining these concepts. Exactly the kinda person we want our teachers to be like. SOOOO glad this channel features her repeatedly. Thanks Big Think and Michelle!

  9. That's the exact moment the nobody knows exactly what's going on, but all theories is available.

    The acceleration was a very interesting surprise because there are unknown forces playing a spectacular role that stimulate creativity and perception of the supergalaxys and superclusters!

    Excelent presentation about the most intrigued mistery of all times!

    Congrats! 🖖🏾

  10. Recent scishow space episode basically says that dark energy will never be stronger than gravity at any smaller scales than the distances between galactic clusters. (If I understood correctly)

  11. she explained it better.. it's not the fact that expansion of space doesn't happen here it's just that it's too gentle to effect compact things that are under the effects of enough gravity..

  12. for scientists very exciting. For me personally with a life expectancy of less than 30 years – trivia. So it is all relative!

  13. All i could think of while listening to this, is that if Melissa McCarthy was a teacher, this is probably what she would sound like.

  14. Hey Michelle , Andromeda is much bigger than milkyway galaxy , are we moving much faster than Andromeda towards Andromeda?hope you understand and answer !

  15. Or… Expansion was an attempt to explain a fundamental flaw in our understanding of Energy and Matter, and is completely wrong.

  16. redshift is lost energy in deep space. Expansion makes new space, which creates new vacuum energy. Are these numbers correlated in any way?
    Is it possible that the conditions of deep space are within a range where photons can decay? Could decaying photons be creating new space?

  17. Let us do some thought experiments and name some facts, trying to check the Big Bang theory.
    1. How large would our galaxy be if it is built only from H and He atoms, containing the same mass as present Milky Way galaxy.

    2. How large would our galaxy be (according to 1) if H and He atoms were smashed to subatomic particles.

    3. Now think of Black Holes and accretion disk that surrounds the Black Hole. All matter is converted to gas due to friction and the gas is shining. The Black Holes are evaporating something. The evaporated particles are pushed away from galaxy, like star dust from newly born star.

    4. We are observing gravitational lensing in the universe, but at some observed locations there is no black hole, nor other visible matter.

    It looks like that the Black Holes are just holes and there is nothing inside. They act as low Cosmic pressure, and what we observe as Black Hole is just the eye of this low pressure. The high pressure is represented by so called Dark Matter, which is ejected by the black hole. The matter as we know it is smashed in the accretion disk, transformed to subatomic particles which are the Dark Matter itself.

    Thinking this way could explain some gaps in our thinking about Cosmology like; what holds spinning galaxy together (Coriolis force), the dark matter (a cloud of subatomic particles), and the dark energy that pushes the universe apart (Black holes are evaporating huge amounts of less dense black matter).

    The question that remain; is forming of galaxies cyclic process (new H atoms are formed from dark matter) or there was really the Big Bang (not likely in my opinion).

    And what if light decays as it travels through space medium. I mean not just dimming but shifting the light spectrum toward lower frequencies?

  18. This is old news. "Big rip" is just the latest marketing attempt for science to appeal to the masses by scaring them. Theres no evidence that a big rip will happen. Just a hypothesis, and a scary one, so it plays well on TV. I didnt hear anything about how Andromeda attained its vector.

  19. I wonder if expansion is accelerating because as galaxies and clusters of galaxies move apart from each other, their weak mutual gravitational attraction continues to get weaker due to the inverse square law, reducing gravity's drag on the expansion and thus allowing the expansion to get faster as there is less gravitational force for it to push against. Maybe expansion doesn't follow the inverse square law, and instead remains constant.

  20. Michelle, do stars and planets emit some sort of frequencies (other than light spectrum), like white dwarfs and black holes? Can we determine a type of celestial body regarding frequency emitted?

  21. "The Andromeda Galaxy and our Milky Way are on a collision course that will obliterate life on Earth 4.5 billion years from now" — what's the basis for the statement on the effect on life on Earth? Other channels say a merger of galaxies is harmless.

  22. Thank you Michelle love you.please explain about dark energy and dark matter.what are they and how do they work?

  23. A eureka moment!
    As we age, we get larger/bigger not because our metabolism slows or we become be less active.
    Instead, our longevity by nature exposes us to more dark matter!
    We're not lazy sloths after all.
    Turns out we're victims of quantum mechanics!

  24. I'm sorry, but why, is a stupid question. The question should be how. This is not meant to be demeaning, but corrective.

  25. What happens to the super massive black holes of two galaxies when they do collide?  Do the black holes themselves collide? does once just steal matter from the other as they pass only to circle back around again ?  Would two black holes ever be able to orbit each other?

  26. Compared to the rest of the universe, is the Andromeda galaxy heading for the Milky way, or the other way round?

  27. Question: I understand that by space expanding then there is new space and time being created as the expansion of the universe is ongoing. Does this mean that time expands as much as space does? is there new time being created along with the space as it stretches? The more it expands the more volume it occupies, hence more space and more time out of basically no where that we know of yet.

  28. Michelle, you a joy to listen to. And this video answered the question i've been wondering about, why we aren't ripped apart by the expansion (at least for now.) 😉

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