star very close to one end of the ellipse. And every time the planet comes close to the star, that's when the gravitational force is the strongest, when the two objects are closest together, causing the planet to speedup. and the star speeds up in response and that's what produces this big spike of acceleration that we saw in the
And when I saw this man talking about the number-- the googolplex-- and talking about gravity, gravitational waves, and this is how everything works, in a way that I could understand-- I was just a child-- that really sparked my interest.And I, from that moment on, said, I want to be just like Carl Sagan.
Some of you know about neutrino astronomy, and that's a different messenger. Gravitational waves are a completely different messenger on the universe.The collaboration that I'm part of is the NANOGrav collaboration.
um I've always wondered this I still can't cck it are you actually weightless or does it just feel like you're weightless cuz you're still gravitational force are you high enough like what what is it a sensational weightlessness or is it technically weightless I've always been curiousabout yeah so you're weightless relative to the airplane got it right so so the airplane is diving down toward the
He's also someone who, together with Henry Cavendish, created a special type of balance that enabled them to make the first accurate measurement of the Earth's gravitational field, gravitational acceleration at the surface of the earth and, therefore, deduce the mass of the earth or the weight of the earth.Why he ended up as a Reverend, we don't actually really know.
everything in the universe that has energy there's nothing in the universe that exists but does not create a gravitational field when we orbit around the Sun the reason in general relativity why the Earth moves around the Sun isbecause it's moving in a curved geometry the Earth is trying its best to move in a straight line but there are no
So play this -- take this technology and play it forward with much greater capability. gravitational signs of matter but we can't explain it with stars or planets or other baryonic matter. So I'd say the laboratory we're doing the
When you try to transform it from one frame of reference to another, it doesn't remain the same quantity in different frames. The gravitational energy you might observe in one frame completely disappears in another. - And Einstein, you know, he had some strange thoughts about this.
There's a story that Oppenheimer was sitting outside of the auditorium when Wheeler was coming forth with his declaration, that in fact black holes were the likely end-state of gravitational collapse for very, very heavy stars. And when asked about it, Oppenheimer sort of said, "Well, I've moved on to other things." - Because you've written in many places
Mhm. Why? Why are they going around the sun like that? Okay, it's because this exerts gravitational force that is pulling these things toward toward the sun. The Earth is just one.
You either do that at the start. the gravitational weight of the fat layer on top of the milk.
So unlike all the other wavelengths that we think of, which are all, finally, forms of light-- radio waves, x-rays, gamma rays, these are all forms of light-- but gravitational waves are a completely different, new messenger. And we've only just begun to open this window on the universe.
But this event, gravitational wave event 15/09/14, on the 14th of September 2015, is the first direct detection of gravitational waves. And you can see here the waveform at Hanford, the waveform at Livingston, Louisiana, and then below it the comparison to the theoretical models for what it should look like if two massive black holes basically merge with each other and emit a burst of gravitational waves.
And so now we need to make a detector that is the size of our entire galaxy in order to be able to detect these very low-frequency, very long wavelength gravitational waves. How are we going to do that? And this is where, of course, we bring the first part of the talk back into the picture.
Here are lots of our student meeting pictures. individual gravitational wave sources.
So that's what makes a supercomputer. The gravitational waves-- I mean a neutron star is the mass-- it's bigger actually than the mass of the Sun.
You see that my clock, being relatively high up in the Schwarzschild geometry, runs faster because I'm experiencing less gravitational redshift. And Frans's runs slower. But then Schwarzschild geometry is really all around us.
Just by the nature of space and time, everything gets stretched and squeezed into an infinitely thin line. this gravitational collapse is happening, where time completely flips on its head and drags everything down to a singularity, to paraphrase Carl Sagan, it's an extraordinary claim.
Just by the nature of space and time, everything gets stretched and squeezed into an infinitely thin line. in gravitational radiation.
That's an important piece of context to the discovery when it did happen, because you've got to realize that when these people were thinking they were seeing a gravitational wave in 2015, this was against a background of nearly 50 years of shooting down every single claim that had ever been made to have seen a gravitational wave. And there was a lot of paranoia about and a lot of enmity about because the rest of the physics community
a gravitational wave in 2015, this was against a background of nearly 50 years of shooting down every single claim that had ever been made to have seen a gravitational wave. And there was a lot of paranoia about and a lot of enmity about because the rest of the physics community generally felt that their money was being wasted by these idiots trying to detect gravitational waves.
Did you hear this? And gravitational waves were cited as ripples in the shape of spacetime. That's what everyone always says.
And that's where the gravitational waves come in. So gravitational waves are a way of observing the universe, but not through light. The gravitational -wave observatory that made that discovery is not a telescope of any kind.
So gravitational waves are a way of observing the universe, but not through light. The gravitational -wave observatory that made that discovery is not a telescope of any kind. It doesn't take pictures of the sky.
place giving rise to a large classical force field such as the force field that is holding us onto the Earth via Gravity the gravitational force is mediated by bosonic particles called gravitons also you can see things in the universe because you're getting electromagnetic radiation which is a classical force field constructed from many many bosonic
rise to a gravitational field so if we want to know what exists in the universe all we have to do is find out what are the gravitational fields in the universe and then we will locate the stuff that is causing them well how do you do that there's many ways of doing that one nice way is through the phenomenon of gravitational lensing If gravity is the curvature of SpaceTime and everything
Take the gravitational potential of a single star for example, well, we could just add 10 to each value of the potential,
which could refer to gravitational force… or gravitational force.
So the gravitational force is relatively strong when you're nearby, relatively weak when you're far away.
and that's primordial gravitational waves.
So the first gravitational wave that we detected was from the collision of two enormous black holes.
And the gravitational waves sort of rippling out from this epic collision are about 1,000th the size of a proton when it comes
If a gravitational wave has gone by, it's squished one arm and stretched the other so you don't quite get the lasers arriving back at the same time.
with being countered by gravitational forces, et cetera.
Maybe it can have ripples in spacetime itself. And those are gravitational waves. So Einstein's conception implies the existence of gravitational waves.
And now we can put the story together, and we can say, OK, so we have supermassive black holes merging. Can we detect gravitational waves from those? Well, what are the timescales?
It is the gravitational force that gets you out of bed every day and brings you to work and has you excited to be here.
It's the anti-gravitational force that's creating the expanding universe.
There's also the gravitational wave.
And those gravitational waves, we claimed, could only have come from inflation.
We had the gravitational waves just discovered last year.
OK, so now we're going to just explain a little bit about what I mentioned before, where the character of spacetime changes completely once this gravitational collapse happens. So what I mean by that is outside a black hole, like this spacetime is what's called static.
Just by the nature of space and time, everything gets stretched and squeezed into an infinitely thin line. This was the first gravitational waves detected by the LIGO collaboration that represents the in-spiral and merger of two black holes.
Just by the nature of space and time, everything gets stretched and squeezed into an infinitely thin line. One polarization-- if the gravitational wave is moving, at one instant it'll stretch the screen in a horizontal direction, while simultaneously
Just by the nature of space and time, everything gets stretched and squeezed into an infinitely thin line. are these gravitational waves and how is a black hole really producing them?
Just by the nature of space and time, everything gets stretched and squeezed into an infinitely thin line. So in gravitational waves, it outshines all the stars in the universe at that one instant.
And then from the mid-90s to the mid-2000s, I went to every single gravitational wave conference that took place around the world and got to know the gravitational wave scientists really well. I mean, one of the very senior people was staying with us for the weekend just last weekend, actually, because we've become friends.
They were technical questions. And the nine other gravitational wave physicists were asked, which one's the real gravitational wave physicist? We've done a lot in Cardiff.
We got not just me, but other people to answer the questions, not just me and a gravitational wave physicist. We got three gravitational wave physicists to answer the questions. We got what I call three savvy physicists to answer the questions.
And you'll see the way the four gravitational wave physicists-- you could get a maximum of 32 points if you answered every question right. And the three other gravitational wave physics got an average of 27 points, and I got 25 points, which isn't bad, whereas the non-gravitational wave physicists, crucially, including the savvy physicists who didn't know anything about gravitational waves, got considerably less points.