Virtual Reality 360°
Filming the Speed of Light at 10 Trillion FPS
The Slow Mo Guys
Mar 27, 2019
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Today, we're at CalTech,
because in a building over there
is a camera that absolutely blows my mind.
Now, we've filmed at some very high frame rates.
We're talking up to about half a million, which is...
- Not to be sniffed at. - ...serious frame rates.
Their camera puts ours to shame
and does 10 trillion frames per second.
That's 13 zeroes.
For reference, that is 20 million times faster
than the fastest we've ever filmed on this channel.
And there's not much you can't film
with half a million frames a second,
but one of those things is the speed of light.
- Not a bad subject. - No.
- Let's get in there. - All right.
Even the shoe cover technology is cool.
I kind of want one of these at home, actually.
- Just for people. - All right, let's go in,
see what this CUP is all about.
- Nice to meet you. - Man: Nice to see you.
- How's it going? - Good.
So, what's actually--
what are we doing here? This looks all very complicated.
Oh, this is the world's fastest camera.
Oh, okay. Yeah. This is the world's fastest camera.
There you go. Just as easy as that.
How big is the actual camera part?
I can show you.
That big box is the camera itself.
And here is the optics that we designed
- to make the thing work. - Very cool.
A lot of times in our YouTube comments,
we get asked to film the speed of light.
And I have to always reply to people
letting them know that the speed of light,
it's almost incomprehensibly fast,
and even our cameras, under a million frames a second,
will never see anything like that.
Is this camera capable of filming the speed of light?
Yeah, that's basically what we are gonna see.
For the example I'm going to show, the light will move
about the length of this bottle.
In time, how long does it take for light to start here and end here?
It takes about 2,000 picoseconds.
- That's pretty quick. Yeah. - Pretty quick.
So for the audience, it goes milliseconds, microseconds...
- Is it nano-- - ...nanoseconds,
- picoseconds, femtoseconds. - Yes.
So we're on the sort of pico/femto scale with this stuff.
- We've never done that before, for sure. - Yeah, no.
This is completely on another level.
Shall we set up the first experiment?
- Sure, yeah. - Start with the bottle?
- Everyone should wear laser goggles. - Goggles?
- Okay. - Peng: We have some.
- Do I look good? - You've got side panels in your glasses.
- You look like you're about to-- - You look bad-ass.
It looks like you're about to go skiing with a welding torch.
So, I assume because we're trying to film light,
it'll be useful to turn all the lights off in here, right?
- Yes. - Otherwise, we'll just get...
All the ambient light comes, yeah.
Let's get ready for lights off.
- Can you hold this for me? - I'll hold this.
- Yeah, thank you. - I'm excited.
I get giddy by this frame rate stuff.
We want to see the light propagation from the side,
so we need to make sure that the light is scattered out of the plane of view
through the milk molecules inside,
then you can see light scatter from the side.
So, this is a bottle full of water with a bit of milk in?
So, I am going to turn on the laser.
So all you do is just move mirrors and lenses around
and then it goes to different areas?
We use that to move the laser. The laser's too big.
See, the light hits the bottom of the bottle.
So it goes through the bottle.
- Is it a powerful laser? - It's very powerful.
It can basically burn any, like, papers.
- I will stay away from that. - Yeah.
- Whoa, that's cool. - You can see its glow.
The first thing I'm going to capture
is the static image
as our reference.
For today, I'm going to try...
- Excellent. - Yeah, yeah.
I mean, I remember when I was excited
when we started shooting,
we moved from 1,000 frames a second
- to 28,000 frames a second. - That was a big jump.
Okay, we're pretty much done with the water bottle.
I'd like to take a photo of this.
As you can see, we can only see the light.
We cannot see the bottle and the label on it.
- Yeah. - So, finally, in the movie, we may want to overlap
both the bottle itself and the light.
- Like, composite a real picture. - Yeah, yeah.
So you just take a photo on your phone and that can-- you can do that?
Yeah, you can just use software to overlap these two things.
- Gav: Neat. - Dan: You're in the photograph.
Just photo-bombing the bottle.
Okay, let's watch back our bottle.
This took eight hours to process,
during which time I grew a slightly longer beard.
I had a haircut as well.
All right, here we go.
Okay, so what we're seeing here
is the bottle's just been comped in, basically.
Yeah, this camera only detects the light itself,
which is like a blue-ish laser light,
which is why you don't really see anything else
other than the light looking like that.
And then we comp in the picture of the bottle.
In the room with my actual eye,
it looked like it was constantly lit up,
but here we're able to follow
the light moving through the bottle.
It may not look like it, but this is actually real.
It's refracting the photons and that's why you can see it.
But when it's just going through the air,
there's nothing to actually reflect the light.
Yeah, it's only showing up in the bottle.
It is interesting. It almost looks like sort of an '80s film effect.
It does, doesn't it? It looks like--
Like some sort of ghost flying into the room.
But actually, that is light.
Isn't that weird? Look at the scale.
Every frame seems to be ten picoseconds.
And we're just sort of casually
watching this light go left to right
through the bottle, but in reality,
the light is moving a million times faster
than a bullet.
What a mental subject.
Okay, so we've shot light through milk.
- Next experiment? - Yep.
For this experiment, we designed a special cavity.
We call it a chaotic cavity.
When light comes in the cavity,
it will bounce back and forth multiple times
by the mirrors surrounding in the cavity.
- You're almost trapping light inside the-- - Yeah. Yeah, exactly.
What's the purpose of this? This egg thing?
This is to create a water vapor
surrounding the environment so that light scatters out.
- The same thing, like-- - Oh, so you can sort of see a little bit.
- Makes sense. - Yeah, so this is how the system works.
- Turn it on. - All right, let's go do the "experimon."
How long did it take you to learn to use this?
Uh, maybe a few months to get used--
- A few months to get used to it. - Yeah.
Because it's a really complicated system.
It's really complicated, is it? I hadn't noticed.
( both muttering )
Okay, so this is the chaotic cavity
at 100 billion frames a second.
Just like nothing.
Once again, the duration of this video is--
you can't even get your head around
how short an amount of time it is.
That is amazing.
When we were in the room,
it looked like the whole thing was glowing,
but now we can see the individual pulse of light
bouncing around this thing.
Looks like a weird version of "Pong."
This is one femtosecond of laser pulse,
so it's as if you just went like...
- with a laser. - A femtosecond pulse.
And if you pause it, you can see it's just a dot of light.
And it's comped in the shape of the mirrors.
I wonder if you could actually build,
like, a big maze to get it around.
Do, like, a little maze and try to get it in.
- World's fastest maze completion. - Yeah.
- ( trills ) - Light.
Oh, it almost went in the corner there.
It is. It's like the DVD screensaver, isn't it?
You just want it to go straight in the corner.
- So this one's 100 billion? - Yeah.
Should we see what 500 billion looks like?
- All right, so the area is quite small. - Yes.
So there's no way that we can stand in and be filmed by this camera.
But alternative solution-- little mini-figurines of us.
Wait, why is mine-- oh, for goodness sake.
- Again, every time. - So we'll put them on there.
- Flipping heck. - All right.
So, in this experiment, instead of shooting light from the side,
I've changed the beam path to bounce back this mirror,
this mirror, and use a concave lens
to expand the beam to shoot at an angle.
So this is more about scattering light
on the surface of the figurines?
Yes, you're sweeping across the surface of the figures.
Because we're obviously not see-through, so...
This is the static image of the two figures.
Now I'm doing 500 billion frames a second
with two by two coding.
So two by two and a casual half trill.
- ( both laugh ) - Peng: Yeah.
I think we're pretty much done with this one.
This is 500 billion frames a second
of our little figurines,
with a resolution
of 549 by 439.
The footage is played back
at 20 frames a second,
therefore it's slowed down by
a factor of 25 billion times.
I do like that I was able
to successfully photobomb this picture.
I like how it shows up on your nose so much.
All right, I knew you'd say something about that.
It does-- it does get caught by my nose, doesn't it?
It is interesting to see the light scatter
on the surface of something
as opposed to go through our body.
So again, all they've done here is pretty much
comp in our bodies with the light.
So the camera would have got this blue light
and they've just taken a picture and comped in us
and matched it up to where the light hit.
You look miserable in that.
You look like I've just said something awkward,
and you're like, "Ooh."
- Should we do these poses? - Yeah, sure.
And you can see on the time scale
it's a much slower progression of picoseconds.
as opposed to half a trillion frames a second.
All right, that's 500 billion done.
- Child's play. - Child's play.
- Let's crank it up. - All the way?
- Yep. - All right.
Let's do 10 trillion frames a second.
So, Peng, we're at a different camera now.
- Is that correct? - Yeah.
And this one can do up to 10 trillion frames a second?
Yeah, yeah. This is the 10 trillion frames a second.
That's the maximum speed that we can do.
Here we have a sample which contains diluted milk,
about a few millimeters long.
That's all that the camera's looking at, is a few millimeters long?
Yeah, that's how long the light propagates within 30 picoseconds.
Dan: Okay, wow.
Here is the same software
that we use to capture the image.
So for this one we're allowed to keep the lights on?
Because we are doing ultra fast images within a very narrow time scale
there's a minimum amount of light that comes through the ambient light.
- In comparison to the powerful laser. - Laser, yeah.
- It's all relative, I suppose. - Yeah, much brighter.
- All right, cool. - Yeah, this is how it works.
Dan: So this is a much smaller scale
'cause we're using a higher frame rate
capturing a very much smaller amount
of space and time, essentially.
- Yes. - Gav: All right.
This is the light traveling through the milk vial
at 10 trillion frames a second.
- This is the reason we came here. - Yeah.
So on the bottle video,
the light seemed to have gained the same speed.
But then you gotta remember that the scale of this
is much smaller. So this is one millimeter,
it says here, is the distance,
whereas before, it was an entire bottle.
Which shows you that we're actually recording
light traveling through such a small amount of space.
And it's so slow now that our picosecond
has a decimal place to the hundredth femtosecond.
That's blowing my mind for a start.
When Peng turned on the laser,
I didn't see anything at all.
But now we can actually see how it moves.
On this scale of time,
if we fired a bullet through this frame,
it would take years
to go from one side to the other.
And the light is just going, blip.
That really puts it into perspective as well, doesn't it?
I just feel like no human should ever have seen this.
It's like looking at the base of the universe.
I've heard that in the future,
the CalTech team actually intends to increase the speed
up to one quadrillion frames per second.
It's a bit mind-blowing, to be honest.
Gav: We have to leave now and go back to our old
measly hundreds of thousands of frames a second.
Measly, pathetic hundreds of thousands.
Thank you very much, Peng, for showing us your amazing kit.
- Thank you. - Yeah, thanks.
- Thank you. - Learned a lot.
Well, to me, that's some of the most
mind-blowing footage ever.
I mean, visually, it's just a blob
going from left to right.
But to know that that's light--
I would say it was actually one of the most
mind-blowing things that we've seen.
Well, I feel very accomplished.
Hopefully, you enjoyed watching
light move through the air in slow-mo.
Feel free to check out other episodes
from "Planet Slow Mo," and join us in part two,
where we'll be learning a lot more
about how this camera works.
You can subscribe, too, if you want.
We'd appreciate it.
Still not sure I'll be able to understand it after part two.
- We'll do our best. - All right.
.ass (Substation Alpha)
What is the fastest thing we as the human race know of? Gav and Dan try and film that.
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