• Question: -How does the discovery of gravitational waves support the cosmic inflation theory? -Also what exactly are these two things and what new concepts can it introduce?

    Asked by Laila to Daniel, Hannah, Maggie, Ry, Scott on 6 Nov 2017. This question was also asked by Maggie_for_the_win, Arianna.
    • Photo: Maggie Lieu

      Maggie Lieu answered on 6 Nov 2017:

      Gravitational Waves are ripples in space time when 2 massive objects merge together (like 2 black holes or neutron stars), when this happens the ripples will travel to Earth and make everything squish in one direction and squash in a perpendicular direction, but the effect is tiny so we cant feel it. The gravitational wave detectors at LIGO have two 4km long laser beams perpendicular to each other. When a gravitational wave passes through it will change the length of one of the lasers by an amount smaller than an atom!

      cosmic inflation is a period in time when the Universe underwent rapid expansion, just after the big bang (because it was so hot and dense!). This event should have released gravitational waves known as the primordial gravitational wave background. If we ever detect this, then it can prove cosmic inflation (but we have yet to do so!)

    • Photo: Daniel Williams

      Daniel Williams answered on 6 Nov 2017:

      Gravitational waves are ripples which travel through spacetime. But what does that mean? Gravity is caused by heavy objects (things with a lot of mass) causing spacetime to bend around them. If that bending changes (e.g. because two things collide and make a much denser object, like what happens when two neutron stars collide) then the rest of spacetime needs to change shape to account for it. A gravitational wave travels out from the place where the change happened, carrying information about that change, and by measuring gravitational waves we can observe these spacetime-changing events.

      Cosmic inflation is a process that we believe happened just after the big bang, where the universe exploded in size in a very short period of time. We don’t know why (or how) it happened, but we have lots of observational evidence to make us pretty sure it did happen. This rapid expansion would have changed the amount of curvature and bending of spacetime, and so it would have made gravitational waves, and they should still be traveling around in the universe.

      LIGO, the observatory I work for, can’t detect these waves, however, because they’ve been stretched out so much by the expansion of the universe that we need an entirely different way of looking for them. There are groups of scientists trying to do it with things called “pulsar timing arrays”, but we’re probably at least a few years off being able to detect them this way!

    • Photo: Ry Cutter

      Ry Cutter answered on 6 Nov 2017:

      Great Question! Daniel’s answer pretty much covers everything.
      I’d add that unlike photons (particles of light), gravitational waves can pass through the wall created by the big bang that light cannot. This means there’s a strong chance we can see even further back, closer to the beginning of the universe with gravitational waves.
      We call them primordial gravitational waves.

      Ryan

    • Photo: Scott Melville

      Scott Melville answered on 6 Nov 2017:

      Dan’s answer is ace, can’t top that 🙂
      My two cents is that the gravity waves recently discovered (the ‘bang’ from two black holes smashing together out there in space) don’t actually support inflation more than any other cosmic theory. Inflation happened a really long time ago, but these black holes bumped into each other fairly recently, so these two things don’t have too much to do with each other. Ryan and Dan are right that in future we might be able to measure very old gravity waves from the Big Bang, but right now we can only hear the very recent, very nearby noises (which is still pretty impressive tbh!).
      Your question is really super important though, because most physicists are taught at some point or other that inflation is almost certainly ‘correct’ (i.e. that there’s lots of evidence for it), but there are a few other ideas out there which are equally supported – and so exactly what happened around the Big Bang is still very much up for debate (as are most things in science!).

    • Photo: Hannah Middleton

      Hannah Middleton answered on 6 Nov 2017:

      I would just add that there are experiments trying to find evidence of primordial gravitational waves by looking at the cosmic microwave background, which is the microwave-light that we observe all over the sky and comes from the very early Universe. By observing it we can learn about the Universe when it was young. The primordial gravitational waves are expected to leave patterns in the microwave-light, but have not been detected yet. If they are there, then that would be evidence that the Universe went through an inflation period. A few years ago an experiment called BICEP-2 thought they had seen evidence for primordial gravitational waves, but it actually turned out to be some extra noise in the data so they are still searching.

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