What happens when you travel faster

than the speed of light?

You can't, you can't.

I'm Paul Sutter.

I'm an astrophysicist and author and a host.

And today I'm reading questions from Twitter.

This is Astrophysics Support.

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@Kiran76333419.

Will someone please explain what is dark matter.

Dark matter,

a better name for dark matter is invisible matter.

We've noticed through countless observations

in astronomy, that there simply isn't enough stuff

in the universe to account for all the motions and dynamics.

And so we think, 80 to 90% of all the matter

in the universe is simply invisible.

And whoever said it had to be visible.

Yeah, that's our rule is not natures.

@Keatonstone asks, how many

exoplanets have been confirmed to date, please astro-pals?

Hey, I'll be your Astro-pal today.

So as of right now,

we have confirmed around four to 5,000 exoplanets

with more coming online every single day.

And that sounds like a lot,

but we suspect that there are around a trillion exoplanets

in the Milky way galaxy.

So, and what we're hunting for is an earth 2.0.

We haven't found one yet,

but we are finding all sorts of crazy planets.

We're finding planets bigger than Jupiter,

smaller than mercury.

We're finding planets,

the size of Jupiter orbiting right up against the face

of their stars,

where they're literally getting their faces melted off.

@Darrell16519C.

Question for astrophysicists.

Do galaxies spin clockwise or counterclockwise?

Yes.

@Rat69721961.

I just have one question.

Thank you.

Why does a person in space age

at a different rate than to someone on the earth?

So this has nothing to do with space

and everything to do with motion

and acceleration and gravity.

We've learned through special relativity

and general relativity that different clocks tick

at different rates.

So the faster you move in space,

the slower you move in time, the stronger gravity you have,

the slower you move through time.

Clocks throughout the universe are all asynchronous

and out of sync with each other.

@NKB_Sean.

Wonder what it's like inside a black hole.

The inside of a black hole is probably the weirdest place

in the universe.

Outside of a black hole,

you can go in any direction you want up or down,

left or right, front or back,

but you must go into your future.

You are forced to travel into your own future.

Inside of a black hole, you are forced to travel

to the singularity.

The point of infinite density in the center.

No matter which direction you look,

you will always head towards the singularity

and you will reach it in a finite amount of time.

So have fun in there.

@Jesusp1738.

Serious question.

What is a parallel universe?

There's two senses of parallel universe

that come into physics.

One is through quantum mechanics,

where every possible interaction can branch

into multiple different possibilities,

each representing a different option for that interaction.

And another option where the early universe,

underwent a period of rapid expansion

and then different universes bubbled and nucleated off

like soap bubbles in a foam.

We don't know if either of them exists, by the way.

@Whomanbot.

How old is the universe?

These are the things I ponder.

Hey, I ponder these too.

13.77 billion years old,

plus or minus a hundred million years.

@Coffeeicecream.

Can anyone explain to me what are cosmic rays,

before I throw these notes down a cliff?

Cosmic rays are high energy particles generated

in gigantic explosions throughout the universe

that are constantly soaking all the space.

Just don't leave the earth and you'll be fine.

@Dr.David.

What are the properties of planetary systems

and what can they tell us about how they form and evolve?

We have found so many different kinds of planetary systems

in the galaxy.

Like you can take the craziest Sci- fi author

with the craziest idea,

and it still comes up short to what we actually observe

in the real galaxy, with actual planets around other stars.

Take for example, the Trappist system,

the trap is one system.

These are seven earth like planets orbiting,

a red door of star,

where three of them are in the habitable zone of that star.

Meaning, liquid water can potentially exist

on their surfaces.

So we've seen pretty much every combination

of planets out there and stars out there.

We've seen planets around binary stars around triple stars.

We've seen planets around big stars, around little stars,

even dead stars.

We're not quite sure what this tells us about the story

of planetary formation,

because we're still gathering that data.

We're still mining that treasure.

@Swaggyshreksimp.

What is astrophysics and why do I wanna do it?

Astrophysics is the study of all the stuff that happens

in the universe.

And it's awesome.

@Cryptoglitter asks,

I wish I knew more about astrophysics.

Hey, me too.

Like how do binary star systems even work?

How did that happen?

Space, question mark, exclamation point,

repeated several times in a row.

And this is why I love astrophysics

and cosmology and astronomy.

We're just talkin' about the weirdest stuff

in the universe here.

Binary stars are actually the most common kind of stars

in the galaxy.

Because when you form a star,

you've got a big cloud of gas and dust,

and then it collapses to form a star.

We found multiple star systems all over the place.

We were almost a binary star system.

We didn't just form the sun,

but that same cloud of gas and dust led to the formation

of the planets.

And so if Jupiter were 20 times bigger than it is,

it too would have been a star

and life on earth would have been impossible.

@Sadie67655974.

When will the universe end?

Not soon enough, I'm just kidding.

It's probably gonna last forever.

As far as we know,

it is going to continue expanding forever.

Eventually every galaxy will be ripped away

from every other galaxy

and all temperature differences will diminish

until we're left with a cold empty void.

Moving on.

@Louvy32.

Is it possible, the gravity of our galaxy

and what makes up our galaxy is why the speed of light

from our locations seems to be constant.

But in other galaxies and places

in the universe where things are different,

that the speed of light constant is different.

This is a great question because we are constantly wondering

if the constants of nature really are constant.

And as far as we can tell,

every single observation measurement in theory has confirmed

that the speed of light really has been constant.

Seriously, we've tested it.

From observations from the very earliest moments

of the big bang itself,

the speed of light is simply the speed of light.

And if the speed of light did change,

would totally mess up physics

and make our lives a lot harder.

@Gmlmusic.

A casual question for astrophysicists:

Hey, let's chat.

How many dimensions are there?

Four. We know that we live in a four dimensional universe.

Three of space, one of time,

inner woven into a fabric that we call space time.

There might be more big dimensions or small dimensions,

but those are all speculative theories.

@Michelfloyd.

Today's astrophysics question:

Does the spin of a galaxy influence the spin

of other nearby galaxies? It must.

It must not. It doesn't.

They're billions of light years away.

@Jhatman8, says what caused the big bang?

It's hard to believe

that a microscopic particle started the big bang.

Another option I just thought of is a large vacuum

in a large pressure collided and boom.

We don't know what caused the big bang.

We don't know what started the universe.

Our models of the universe take us

to the very earliest moments,

but without a theory of quantum gravity,

we don't know what started it all.

We don't even know if that question even makes sense.

@Eggisoph asks, what happens when you travel faster

than the speed of light?

You can't. You can't travel faster than the speed of light.

I'm sorry. You just, can't.

You see, as you get faster and faster,

as you approach the speed of light,

you have more energy

and in relativity energy takes more work to accelerate.

So you end up requiring an infinite amount of energy

in order to travel faster than the speed of light.

And so it's just for forbidden.

And when I watch a movie, you know,

they're in this spaceship and they press the button

or press the lever and they go faster

than the speed of light.

I don't care.

Because when I'm watching a movie,

I'm not grading homework here folks.

I just wanna sit back and relax and enjoy the show.

@Xavier_html. If the universe is made up of mostly space

and it's expanding, what's at the edge, more space,

the source wall,

something beyond human comprehension?

At the edge of the observable universe,

is just more universe.

The universe is larger than what we can observe

because light can only go so fast

and the universe is only so old.

However, we don't know how big the universe really is.

It could be infinitely big,

or it could just be very, very, very large.

But no matter what,

the universe doesn't have an edge,

it's not expanding into anything.

It has no center. It has no edge.

I know it doesn't make any sense, but, you know,

since when has science ever made any sense.

@Powellds. Astrophysics question.

If you time traveled exactly 30 years into the future,

you would not be where you started, but in space. Yes?

Yes.

@Equalopposite. Astrophysics question.

Is the quantity of dark matter in the universe increasing,

decreasing, or has it remained the same since time=0?

Yeah. The amount of stuff in the universe,

normal matter, dark matter, boring matter,

whatever it is, has been the same.

The density is dropping though,

because we live in an expanding universe.

Every day our universe gets bigger and bigger.

And so it's diluting out all that same amount of matter.

@Schley. Another astrophysics question.

If the earth access wasn't tilted,

would there be any way to directly observe the passage

of a year?

Yeah. Good, good point here.

Because it's through the access of the rotation of the earth

that we get our seasons and the transitions of the seasons.

But even if we didn't have that tilt,

we would still be able to notice the passage of a year

because of the stars that we would see.

As we go around the sun in our solar system,

we see different sets of stars on our night sky

and it rotates continuously through the year.

So any one who can observe the night sky night after night,

over the course of the year, would be able to figure out

that we do have a year.

@thin_linz. If you have a car that travels faster

than the speed of light, what happens when you turn

on the headlights?

First, can't travel faster than light.

But no matter how fast you're going,

the light always comes out of your headlights at the speed

of light, because that's what light does.

Here we have @Upulie.

Hi there.

Hello.

I have an astrophysics question.

My question is, is the structure of the universe,

as it stands at its current level of expansion,

related to the original singularity that resulted

in the big bang?

Hmm, not quite.

At the very largest scales,

we see something called the cosmic web.

It's the very largest pattern found in nature.

It's literally made of galaxies.

But the cosmic web had its origins

but in the earliest moments of the big bang,

where quantum fluctuations in space-time itself led

to tiny little density differences.

And then over the course of billions of years,

these density differences grew up to become clusters

of galaxies in the great cosmic void.

@Pwbrewer. Question for astrophysicists.

That's me.

How far from earth could you detect a Hiroshima sized,

atomic blast with our technology?

Like yay far.

We'd probably spot it on the other side of the solar system,

but that's it.

@Roughschrade. Whenever I read about science,

I find I'm woefully out of depth.

How can quasars produce radio waves

and why can't I listen to them?

Radio waves come from a,

you take charge particles and wiggle them around,

and it generates radio waves.

So quasars are spewing out charged particles.

They make radio waves and you can listen to them.

We detect quasars with radio telescopes and radio antenna.

So you can, you're just tuning into the wrong station.

You need a quasar FM.

@Arten-zin. Astrophysics question into to the void:

Should it be possible to blow up a black hole

from the inside?

No, but they naturally dissolve through Hawking radiation.

You just need to wait like 10 to a hundred years.

And that's not 10 to a hundred,

that's 10 to the hundredth power years. So be patient.

Thank you for all of these amazing questions.

I hope you learned something about astrophysics.

I hope I was able to help and I hope you had

as much fun as I did.

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