Visualising gravitational waves

when LIGO announced that they detected gravitational waves earlier this year we were inundated with artistic renderings of gravitational waves fantastic images like this one produced by the LIGO team themselves that help us to visualize this weird phenomenon but in all the graphics that I've seen there's a kind of disconnect between the objects and the waves that they produce there's no way to see how one causes the other and I think we can fix that with an actual physical demonstration of gravitational waves my plan is to take a classic demonstration of the warping of space-time and just push it a bit further see if I can get it to demonstrate something it's never demonstrated before I'll run through the standard demonstration first so here we've got a sheet of lycra imagine that this is our universe or at least a two-dimensional version of our universe and just like the real universe when you introduce a massive object it warps space-time and just like in the real universe when you warp space-time the paths of other objects Bend around like that so there you go we have maybe a moon orbiting around a planet that's pretty cool actually I'm quite pleased with this because this ball here looks a lot like Mars and the reason it looks like Mars is because it's rusty is covered in iron oxide and Mars is that reddish brown color for the same reason it's covered in iron oxide but anyway you can also simulate a massive object in this universe by pressing your finger into it like this so there you go I'm warping space just in the same way that a massive object would and if I want to simulate a more massive object I just push harder that will become important later this analogy for the real universe is OK it's not perfect in fact I touch on some of the imperfections in the previous video about like it that I made with my wife where we discuss gravitational waves but this universe does have something in common with the actual universe that makes it really good for demonstrating gravitational waves and that's a speed limit so our universe has a speed limit of about 300 million meters-per-second nothing can travel faster than that most things travel slower than that some things travel at the speed limit so light for example travels at the speed limit of the universe which is why we call the speed limit of the universe the speed of light and so you probably know this the Sun is very far away so it takes light about eight minutes to reach us meaning that if the Sun were to suddenly go out we wouldn't be aware of it for another eight minutes and it's the same with gravity gravity travels at the speed of light so if the Sun were to suddenly disappear we wouldn't be aware of it we wouldn't feel the gravitational effect of that for another eight minutes and I can demonstrate that in this universe here so if I suddenly introduce a massive object into this universe let's watch that in slow motion so you can see this region of space isn't yet aware of this new massive object that's been introduced into the universe because that warping of space-time is traveling outwards from the source at the speed of light and there you go only now does it feel the effects of that massive object of course in the real universe objects don't suddenly disappear or appear but they do move so you know if I have a massive object here and I move it over there then objects in the distance over there won't feel that change in the warping of space-time until it's propagated over that distance and this is how we can demonstrate gravitational waves so what we want is two black holes orbiting each other this is what LIGO detected so I can have maybe my two fingers pressing into the fabric and I can orbit them around each other I actually get a little bit stuck because I can't pass my arms through each other so I've built something I've built this device here so I can spin this around in my universe and you'll notice we're not seeing any gravitational waves that's because I'm not spinning this thing fast enough at the point that LIGO was able to detect gravitational faves those obviously black holes those orbiting black holes were traveling close to the speed of light so I need to spin this thing close to the speed of light fortunately for me not the speed of light of the universe but the speed of light of this universe and I can calculate the speed of light of this universe if I look at this slow-motion footage here I can eyeball the distance so I can calculate that it takes about 32 frames of footage to travel about 20 centimeters and we're looking at 1200 frames per second so the speed limit in this universe or the speed of light in this universe if you like is about 8 meters per second so I need my black hole's to be moving at about 8 meters per second so how many turns is that per second well the radius of the orbit is no point not seven meters meaning the total circumference of the orbit is about naught point four four meters so I divide eight meters by nine point four four that gives me about 18 turns per second I need to spin this 18 times every second which I'm not gonna have to do with my fingers but that's okay because I brought a drill but that's okay because I brought a drill okay here we go well I look quite promising let's let's have a look at that in slow motion you how cool is that an actual physical demonstration of gravitational waves couple of extra things firstly one thing that this universe doesn't have in common with the actual universe is that it has an edge and so far as we know the actual universe doesn't have an edge and if it does then it's so far away that it isn't interesting in terms of this discussion here but when you have an edge like that in physics it's called a boundary condition and if the boundary conditions are right waves get reflected and you can see that in this video here you can see the waves being reflected Einstein's equations of gravity allow for all sorts of things that we don't observe in the universe like wormholes for example they're not explicitly disallowed by Einstein's equations of gravity so maybe we'll find them one day and I wonder if boundary conditions are allowed there in Einstein's equations of gravity as well I don't actually know so if you've got any thoughts on that please let me know the other thing I wanted to talk about was how I captured the slow-motion footage of the gravitational waves because I didn't use a slow-motion camera instead I utilized the stroboscopic effect and the way the stroboscopic effect works is if you've got something that repeats again and again and again then you line up the framerate of your camera with the speed of repetition of the thing you're trying to film so because the gravitational waves were repeating it wasn't you know the same thing again and again and again I was able to use this stroboscopic effect so imagine this imagine you've got this thing and you set your camera to one frame per second and you also rotate this thing once per second so it spins all the way around and you take a frame it spins all the way around again you take another frame you spin it around up again you take another frame there you take another frame there and so on you keep going every time so if you play all those frames together it just looks at that frame one frame to frame through frame for frame five it looks like it's stationary so if you then speed the thing up so it's actually going slightly faster than 110 per second then you know you take a frame it spins around and then you take it to the frame there and then you take another frame there and then you take another frame there so when you go through the frames now it's like there there there there there there there so the thing is slowly moving around so my camera was running at 25 frames per second so in the UK you have a choice of 25 or 50 whereas in America it's 30 or 60 I'm not going to get into why because people have already made great videos in fact Tom Scott has made a great video link here about why there's a difference in the two countries but suffice to say I needed to spin this thing at about 18 and so either faster or slower than the frame rate of the camera but I also needed to spin it close to the speed of light in the universe so it's been right in the universe was 18 times I need to spin at 18 times per second to match the speed of light what does it need 25 frames per second for the camera so actually had to speed up the speed of light in the universe to catch those frames so after I did that bit about how fast I had to spin it I then tightened the fabric on the frame to speed up the speed of light in my universe to get it to the speed I needed it to be anyway I hope you enjoyed this video if you did please hit subscribe and I will see you next time

Channel: Steve Mould

Views: 1,049,979

Keywords: gravity, ligo, Einstein, spacetime, explaination, understand, black holes, general relitivity, lycra, how-to

Id: dw7U3BYMs4U

Length: 10min 38sec (638 seconds)

Published: Tue Aug 09 2016

Reddit Comments

[u/Sogemplow]

From quite a while ago but its pretty neat to see how the waves come off of the merging objects. A lot nicer than the wifi symbol with a black hole we kind of end up seeing.

[u/nanonan]

A naive layman question, if we need to add a dimension to demonstrate 2d gravity, why do we not add dimensions for gravity itself?

[u/nuclearfission]

What happens if you press too hard with your finger?

[u/SPH3R1C4L]

What was like, the big thing about this though? Confirmation that gravity moves at the speed of light?

[u/[deleted]]

This guy looks like he seriously needs some sleep.

[u/danieltagme]

Amazing Work! Congrats!

[u/KimoAwesome98]

What type of material is that.

[u/sicknoto]

I feel like this helps me visualize why it was a satisfying dwoop sound

[u/AlexanderNoys]

Every Steve Mould's video is amazing.