(upbeat instrumental music)
- One of the great things about making videos on YouTube
is the feedback that you get in the comments.
(sobbing)
Not that sort of feedback, I mean the feedback you get
from really clever people watching your science videos,
like, you'll get someone who works in a particular field
that the video is about, giving you extra insights,
or you'll have someone asking probing questions
that you hadn't thought to answer in the original video.
I asked recently on social media, are there any videos
that you really want to see a follow up on?
And a lot of you said that you wanted to see a follow up
on the gravitational waves video,
but where I spin the black holes
faster than the speed of light.
What a great idea.
If you haven't watched the original video yet,
I recommend you do that first, the link is in the card there
and in the description, but a quick summary,
gravitational waves are essentially ripples
in the fabric of the universe
and we detect them here on earth
when distant massive objects like black holes
move backwards and forwards really quickly.
For example, if they're orbiting around each other.
And so I'm representing the fabric of the universe
with this literal stretchy fabric
and I'm representing the black holes with these wheels.
Massive objects like black holes
warp the fabric of the universe.
So I'm simulating black holes,
warping the fabric of the universe by pressing the wheels
into the fabric, and look,
you can see as the black holes orbit each other
that backwards and forwards motion causes ripples
in the fabric of the universe to radiate outwards,
and they'll eventually reach our detectors here on earth.
In my simulation, I was spinning my wheel black holes
close to the speed of light in my fabric universe.
And you can see what the speed of light in my universe is,
because the speed of gravitational waves
is also the speed of light, so look,
this ripple, this gravitational wave
is traveling at the speed of light in my universe.
This is slow-mo footage,
the actual speed is about eight meters per second.
So, I was spinning my black holes
just below eight meters per second.
And your question was, what happens
if you spin those wheely black holes
above the speed of light in my universe,
above the speed of gravitational waves.
In the original video I was able to capture
a kind of fake slow motion footage
using the stroboscopic effect.
Unfortunately, you can't use the stroboscopic effect
to capture faster than light travel,
you need an actual slow motion camera.
Fortunately, Destin from "Smarter Every Day"
was visiting me in London a few weeks ago
to film a collaboration video.
Link to that in the card in the description as well.
He brought his slow motion camera with him
and he was out for the day, he went to a conference
and he left the slow motion camera with me to play with,
so I was able to capture this slow motion footage
of faster than light travel.
So look, when you get to the speed of light
the wavefront bunches up in front of the black hole
and if you go a little bit faster than the speed of light,
that bunching up in front of the black hole
generates these ripples
that propagate behind the black hole.
A bit like the wake of a ship,
which totally makes sense actually
because ships tend to travel faster
than the ripples across the water that they create,
so you end up with this triangle behind the boat.
It's also like breaking the sound barrier.
You have this cone of sound that propagates outwards
behind the aircraft.
Sound waves interfere constructively
at the surface of the cone,
so you get a spike in amplitude.
You experience that as a sonic boom
as the cone passes over you. (bouncing instrumental)
And you can see a similar thing here.
When you get past the speed of light, these ridges form
which is like the spike in amplitude
you experienced with a sonic boom,
where the ripples
are constructively interfering with each other.
That's my hypothesis anyway.
In a minute, I want to show you the disastrous consequences
of going much faster than the speed of light,
'cause it's really interesting, but first,
I want to just quickly answer a follow on question
that a lot of people had, so, a lot people said
can you show us what happens when you go
faster than the speed of light and would that be
a good illustration of what happens in our universe
when we go faster than the speed of light?
And I think the answer to that question has to be,
no, it would not be a good model of what happens
when you go faster than the speed of light in our universe.
Because, in our universe
you simply can't go faster than the speed of light.
And you might say well, okay, yeah.
Technically you can, but like imagine if you could,
would it look like that?
And I still think the answer has to be no,
because, well there's a couple of good reasons
why you can't go faster
than the speed of light in our universe.
The first is, as you get closer to the speed of light,
it takes more and more energy to accelerate
to the point where if you actually wanted
to reach the speed of light, you would need to input
an infinite amount of energy to get there,
it's not possible.
The other issue is if you go faster than the speed of light,
it breaks causality, so cause doesn't follow effect anymore.
You can travel back in time and kill your grandfather
before he gives birth to your father
and create those kinds of thought experiment paradoxes
that you hear about.
So, two good reasons why not and you might say, yeah, okay,
but like, if you could, would it look like that?
Here's why I think the answer is no.
Because well, it comes down to
the way we build models.
If you have a model for the universe, it's really important
to probe the limitations of that model.
Like, the model that I have here
is essentially a model of Einstein's description of gravity.
So, Einstein says,
massive objects warp the fabric of the universe
and I'm showing that here,
except what he specifically means is
massive objects warp space time.
Space time is this four dimensional thing,
three spatial dimensions and a time dimension,
they all get warped and I'm clearly not doing that
in my model, I'm warping two spatial dimensions.
I'm not warping time at all,
so you don't get Lorentz contractions,
you don't get time dilation,
you don't get any of that good stuff in relativity
that lead to these mathematical singularities
that you can't go beyond.
That means you can't break the speed of light
in our universe.
So, the reason this model isn't a good description
of what happens in our universe
when you go faster than the speed of light
is because this model is limited
in terms of its explanatory power.
Like, it's a good way of explaining what happens
when an object that warps its surroundings
moves backwards and forwards.
When it moves backwards and forwards,
the warping of its surroundings
travels outwards like a wave and that's a good analogy
for the detection of gravitational waves.
We're essentially detecting
the backwards and forwards motion of black holes
when they orbit each other.
But beyond that, the model starts to break down
because we're not really warping space time
and we're certainly not warping it
in the strict mathematical sense as described
in Einstein's Theory of Gravity.
But I'm still glad I tried it because, you know,
I'm in the business of trying to explain things
as well as I can, that's what I strive to do
so it's important for me to probe the limitations
of the tools that I use to explain things.
And it's kind of an analogy for how science works,
like, all of our theories are essentially just models
that try to explain the workings of the universe.
Like quantum mechanics is a set of equations
that model the universe.
When you solve the equations, it seems to show you
what we actually observe in the universe,
except that we know the model is incomplete
because it doesn't work for extreme masses and velocities.
And the exciting thing is,
that's when new scientific discoveries are made,
they're made at the boundary
of the descriptive power of the models that we use.
I think we should be grateful that we can't go
faster than the speed of light,
because it's quite dangerous, look what happens.
The fabric of the universe is torn apart
and look, control over those black holes
is ripped out of the hand of God.
So I guess you would Should literally be thanking
our lucky stars.
This video was curiosity driven.
It was driven by your curiosity
to find out what happens when you do this thing.
And I wanna talk about the elements of curiosity
like inquisitiveness.
Obviously that's an important element of curiosity,
like, a willingness to figure out where your ignorance is
and to step into that ignorance
and have a look around, you know,
until that ignorance turns into enlightenment.
Another important element is
seeking out the opinions and ideas of other people.
And that's what I try to do on social media
and in the comments on YouTube.
If you're interested to hear about
other elements of curiosity,
then I encourage you to click on the sponsor link
in the description.
I hope you enjoyed this video, if you did,
don't forget to hit Subscribe and I'll see you next time.
(upbeat instrumental music)