Physicist Answers Physics Questions From Twitter | Tech Support

I'm Jeffrey Hazboun,

I'm a physicist.

Let's answer some questions off the internet.

This is Physics Support.

[upbeat music]

@PAzaz91 asks,

how do black holes influence the space-time around them?

Anything that's massive will bend space-time.

So if I think about this sheet of elastic

as being space-time with nothing in it,

as soon as I put something that has any mass in there,

it bends space-time around it.

If I then take something really small like this marble

and give it a little bit of oomph,

it'll orbit around that object.

And it's that following curved space-time

is why the earth moves around the sun.

So if I have a really big object

and I look at what that looks like in space-time,

that bends it even more.

The key with a black hole is making something

that's really, really dense,

and as I increase that density,

that stretches the space-time further and further

and further down,

so much that light can't escape that curvature anymore,

and that's what we call a black hole.

@petalsforjack asks,

wait, what's space-time?

Space-time is the thing that we live in.

It is four dimensions,

three dimensions of space

and adding to that the dimension of time.

It's what we're moving through as we sit still,

it's what we're moving through as we walk through our house.

@FrvnkieSmacks asks,

how do you split an atom?

What you're really doing is you're splitting the nucleus.

And let's say this is the nucleus of a uranium atom,

and what you do is you shoot another particle at it,

usually a neutron,

really, really fast.

And when you shoot it at the nucleus,

the nucleus breaks into pieces,

into a few different pieces that are smaller nuclei.

And when you do that,

it also, as you can see, releases a lot of energy,

and that's where the first nuclear bombs came from

and that's where the energy we get

from nuclear power comes from.

User alir8203 asks,

if the sun just suddenly disappeared,

it would take us eight minutes to find out.

But does earth still orbit where the sun was,

or will it go out of the orbit

immediately after it disappeared?

The answer is it's gonna keep moving around the sun

for another eight minutes.

We don't know here on earth that the sun disappeared

because it takes eight minutes for the light

to get to us from the sun.

It also takes eight minutes for any changes in gravity

to get from the sun to us.

@Mike_Bianchi asks,

hasn't read a God-damned thing about physics

since high school.

Hey, did you hear about the gravitational waves?

I have heard about the gravitational waves

and I helped publish some of the recent results

about gravitational waves.

In case you haven't been paying attention,

gravitational waves are these expansions

and contractions of space-time

that are traveling through space-time at us

from super massive black holes

at the centers of faraway galaxies.

One of the really neat things about gravitational waves

is they pass unimpeded through the universe.

We can actually get closer to the Big Bang

using observations of gravitational waves.

So they're gonna teach us all kinds of neat stuff

about the early universe.

@only1_66 asks,

one question,

how do you detect gravitational waves in space-time?

The first way we detected gravitational waves

a few years ago was using lasers in big vacuum tubes.

And you split a laser,

you shoot it down two tubes,

and you keep track of how far apart the mirrors are

using the lasers

to tell you the distance between the mirrors.

That's called LIGO.

The second way that we've learned

to detect gravitational waves

is by using these exotic stars called pulsars.

They are really fast spinning stars

that pulse every time they come into our line of sight.

We watch those pulses over time,

if the pulses arrive a little bit later

or a little bit earlier,

we can attribute that to the expansion

and contraction of space-time between us and those stars.

I'm part of a collaboration

that looks at almost 70 of these stars

in all different directions

and we've been monitoring it for almost 20 years.

@thetarekhatib asks,

I'm genuinely paying you $1,000 if you answer this right.

Is light a wave or a particle?

The answer is that light is both a wave and a particle.

We've known the wave-like properties of light

for a long time.

There's a classic experiment

called the Young's double-slit experiment.

Let's show it to you right now.

Let's take down the lights.

We're gonna take a laser pointer here,

which is not how the original experiment was done.

I'm just gonna take this plate

that has a little tiny slit in it

and point the laser through it.

And what happens is it splits the light

into two different waves

and those waves are a little separated from each other.

They're not quite matched up

because two different waves are meeting up with each other,

and this is what we call interfering,

and that's what gives us that pattern.

There's actually two waves hitting there

and they're constructively interfering.

So the black spots are actually the same

as what you get in noise-canceling headphones.

One of the waves is canceling out the other wave,

and only a wave behaves like this.

Lights, please.

Light is actually something bigger

than a wave or a particle,

it's something we call a quantum field

and that quantum field has particle-like characteristics

and wave-like characteristics,

and we can measure both.

So I think you owe me a thousand bucks, dude.

@Dr_Z_GCDisney asks,

what's the difference between fission and fusion anyway?

Do you wanna go fission with me?

I don't want to be anywhere near where fission is happening.

Fission is where you take a nucleus

that's really big of an atom and you break it into pieces.

Fusion is where you take pieces of atoms

and you push them together to make something bigger.

Fusion is what happens in the sun

where really small nuclei come together,

and that is a huge explosion.

And we've been trying to build something like that on earth

to make energy,

we haven't been able to figure out how to control it yet.

Shivanshu21212 asks,

how will the universe end?

The universe will end in the heat death of the universe,

which just means that over time the universe is expanding

and all of the light that we know about

is going to get degraded and absorbed by black holes.

It just gets really cold and really dark.

We won't be able to see anything in the distance

and just nothing.

The heat death of the universe

is not something to worry about

because it's gonna happen 40 to 50 billion years

in the future,

and we're only about 14 billion years

from the beginning of the universe.

@ClwnPrncCharlie asks,

wait, are black holes/wormholes actually spheres?

Watching Interstellar.

Black holes are pretty much perfect spheres.

If they're spinning,

they are a little bit more expanded around their equator

where they're spinning than at their poles,

but pretty much spheres.

So in that classic image from Interstellar,

you see this pretty much spherical black hole at the center

and then you see all of this light,

which is the light from the other side of the black hole

getting bent around it.

And that disk that you see across the front,

that tells you that the black hole is actually spinning.

And every black hole that we know of is spinning,

like every other star in the universe.

@52xmax asks,

what's so special about special relativity?

Well, that's relative.

Einstein, probably.

Special relativity is special for a few reasons.

Number one, it gives us a universal speed limit,

which is the speed of light.

Nothing can go faster than the speed of light,

and that's unique to Einstein.

He figured this out in 1905

and no one had really thought

that there was any kind of universal speed limit.

Couple other things that are really special

about special relativity are that it tells you

if you're moving close to the speed of light,

time dilates, it gets longer.

So if you're moving really fast,

you experience time more slowly

than someone who's not moving really fast.

@cowboyvard asks,

can someone explain the twin paradox to me in simple terms?

You have two twins, both on earth,

one of the twins decides to be an astronaut.

She takes off in a spaceship going super fast,

almost the speed of light.

It takes her 50 years to go out to a star and come back.

When the astronaut comes back,

the twin that remained,

she's 50 years older,

the other twin might only be 20 years old

depending on how fast she was going.

And so it's the person in the rocket

that will see time move more slowly

and will only age 20 years.

@ayresforce1 asks,

the speed of light as constant is falsehood.

What's the speed of light in water?

Slower?

The speed of light as a constant is not a falsehood.

We have a glass of water

and I'm gonna put this pencil in there.

And when I put the pencil in,

the pencil looks bent,

the light that's coming out that you're seeing is bent.

And that bending comes from the fact

that as the light hits it at some angle,

it sort of veers in that direction.

The light's interacting with the water,

it's getting absorbed and remitted.

It's seeing a little bit longer path as it gets scattered,

and it's that that makes the light look like it's bent,

those interactions take a little bit of time,

and that's why we say

that it's effectively moving more slowly.

Between one interaction and the next,

the speed of light is the speed of light.

@aquariusdonkek asks,

the question is, how does time dilation work?

Long story short,

time dilation is the fact

that when you're moving really close to the speed of light,

time passes more slowly.

It's pretty simple to write down.

The time that passes for someone who's moving at some speed

is proportional to how time is passing

for someone who's not moving at that speed.

And there's this funky square root down here.

And what matters is the comparison

of how fast that person's moving,

that's what V is,

as compared to the speed of light.

And in that line there.

And as you go faster and faster and faster,

that factor of delta t prime gets longer

and longer and longer,

so time is passing more and more slowly.

When you get to the speed of light,

time no longer passes.

@neilcameron78 asks,

are black holes really wormholes?

Or are wormholes really black holes?

Eh, eh?

#science.

We know black holes exist.

We can see evidence for them out there.

We've seen light around these black holes

and what it looks like.

We've seen the silhouette of a black hole.

Wormholes are a shortcut through space-time

from one place to another.

The first idea of a wormhole

is something called an Einstein-Rosen Bridge.

It would take moving faster than the speed of light

to travel through.

And we have no evidence whatsoever that wormholes exist.

Some physicists have posited

that if we use some of the special characteristics

of quantum field theory,

that maybe we can create tiny, tiny little wormholes

that we can send a signal through

from one place in space-time to another.

And while these have been successful as thought experiments

and successful as computer simulations,

it's not yet been seen in the real world

in a real-life experiment.

@MATTP1949 asks,

you think time travel is possible

under current physics understanding?

No, probably not,

at least not from what we understand right now.

There's a couple of ways to think about

how we might travel in time.

One way is using a wormhole.

Some physicists have done this thought experiment

and written down all of the pieces you would need.

So you build a wormhole that somehow changes

and tunnels through space-time back into the past.

You write down the math for what that wormhole looks like.

The kind of matter that you would need

to hold that wormhole open

doesn't exist in our current understanding of physics.

The type of matter that you would need

to hold a wormhole open is called exotic matter,

things like negative energy density,

which what does that mean?

It means like thinking of something with negative mass.

So I don't know

if we're going to be building a time machine anytime soon

unless we can figure out how to find

and make this exotic matter.

Brad_alexandru asks,

is there anything infinite in the real world,

or is infinity just a concept in our mind?

Infinity is not just a concept in our minds.

The most important infinity that I study

is that the universe is infinite.

So that's a great example of something that's infinite.

We use infinities all the time

when we're making predictions in physics,

and it turns out that the size of the universe is infinite.

The amount of time the universe will be around

is also infinite.

@OneDayWellBeOk asks,

quick question,

does anybody know the difference between particle physics

and quantum physics, please?

Particle physics is a small part of quantum physics.

And quantum physics is the area of physics

that really studies small stuff

and the interactions on really, really small scales,

but particle physics focuses on the particles

that make up atoms,

the fundamental particles that make up everything around us.

@Cipher707 asks,

I thought quantum physics was a fanfic.

Absolutely not.

Quantum physics is how the world works,

but you have to look at a really small scale

to understand what's going on.

If I throw a ball up in the air,

it comes down back into my hand,

that's classical physics.

Quantum physics acts in surprising ways.

So instead of having pure predictions

about what's gonna happen at a quantum level,

we just get probabilities.

There's a 50% chance that this thing is gonna happen,

a 20% chance that this other thing is going to happen.

If you watch a lot of Marvel movies,

I could see why you'd think it was fanfic,

because it gets used anytime you don't know

how to explain the science that you wanna do.

@ravenbiter asks,

lecturer just asked what Heisenberg contributed to physics

and loads of people answered crystal meth.

That's a different Heisenberg.

The Heisenberg that we know

is a very famous quantum physicist.

He worked with the German government during World War II,

but he's really well known for being one of the people

who figured out all of these rules of quantum mechanics

really early on.

He came up with something called the uncertainty principle.

Basically, if I know one aspect of a particle,

like where it is,

I can't know how fast it's moving very well,

or if I know how fast it's moving,

I can't know where it is.

@tim_amburgey asks,

I just learned about quantum entanglement and I'm shook.

How can two particles be so connected

that they affect each other

even when they're light-years apart?

Is this the secret to long-distance relationships?

#quantumlove.

Two particles light-years apart can absolutely be connected

if we've set them up in a entangled state.

And what that means is we take two particles

where the measurement has something to do with chance.

So if I roll this dice,

whatever value I get on that face,

I'm gonna get the same value on the other dice

if that's how I've set up the entangled system.

And these two particles can be very, very far apart

from each other.

And this is just how nature works.

The weird part about this is the chance

that no matter how I roll the dice,

whatever it lands on,

the other dice will land on the same exact value.

This is just a fundamental way about how the universe works.

@u_tibi asks,

what the hell does the Large Hadron Collider do anyways?

The Large Hadron Collider

is the largest particle accelerator in the world.

It is a huge 10-kilometer circle in Switzerland

where we take two streams of protons.

Protons are a kind of hadron,

hadrons are really heavy particles.

Takes those two streams of protons

and aligns them just right,

they're going almost the speed of light,

not quite, but almost the speed of light,

and smashes them into each other.

The faster you can get those protons to go,

the more stuff comes out of that explosion

when you smash 'em together.

We're making new particles that we haven't seen before.

They're part of nature,

but they take so much energy to make

that they haven't been around since the Big Bang

when the universe was really tiny

and really, really energetic.

So not only are we learning about these fundamental forces,

we're also learning about physics

right at the beginning of our universe.

@PhysicsInHistory asks,

is string theory really a dead end?

No, it's not a dead end.

String theory is a theory that says,

instead of the fundamental pieces

of the universe being particles,

they're strings.

And these strings can vibrate in different ways.

You can have strings that are long,

you can have strings that are in loops.

And not only does it describe all of particle physics

and quantum mechanics,

some pieces of this actually predict

what quantum gravity would look like,

gravity on a really small scale,

which is not a theory that we have right now.

So those are all the questions for today.

Thanks for such insightful questions.

Thanks for watching Physics Support.