Name: Would Headlights Work at Light Speed?
Uploaded: 2019-04-10T12:18:31.000Z
Duration: 12 min 23 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

The second conditional

Hey, Vsauce. Michael here. If you were driving in a car

at the speed of light and you turned on your headlights

what would happen? Would light be able to come out

Or maybe, light would come out but it just pull up

inside the headlight like a overflowing sink.

Or maybe the light would come out but at
twice the speed of light - at its normal

No, that doesn't sound right. None of these
answers sound right because,

But come on, you say, there are things
that can travel at the speed of light.

Things that have no mass, like photons. Let's build a car

Let's take that suggestion because imagining what it is like

to be light, brings up a lot of questions about

light, about why things are the way they are

In order to see what I mean we need to
talk about "C".

It is Constant. As long as you aren't
accelarating, you can move as fast or

in whatever direction you want and you will still

speed. Even when light appears to slow
down, as it passes through different

the actual photons themselves are still
always traveling at "C".

They're just taking a longer path, which takes

more time. This law always holds true
because whenever you move,

relative to other things, your
measurements of them and their

change. When you move, everything not
moving with you appears to you to be

in length and to be experiencing time more slowly.

Whereas to everything else, it is you
that these changes happen to.

These changes really happen - just not
noticeably or measurably at the speeds

For example, while walking to your
refrigerator for a snack,

you will measure your fridge to be a 100 quadrillionth

of a meter nearer and thinner than you
would while at rest with it.

You'll also notice that it experiences time more slowly

than you. Each one of its seconds
will be a 100 quadrillionth

of a second longer than yours. But your fridge

will measure that these transformations are
happening to you.

These are small numbers, but at speeds
nearer the speed of light

these changes can be dramatic. As I
mentioned in an earlier video,

to a particle racing toward Earth at
99.9999999999991%

Now with all of this in mind, let's take a
look at headlights

being used by a stationary ship and one that is moving

The Near Light Speed Ship would be
flattened in the direction of its travel

while a stationary one would not. As their
headlights come on

the light coming from both ships travels
at the same rate.

The speed of a lights' source doesn't
push it faster.

The moving ships velocity does, however,
give its headlight energy

in the direction it's headed, causing a
blue shift from the front and a red shift

What's really cool though is that this
is just what

we would see, floating in space at rest
with the stationary ship.

The crew of the fast-moving ship
wouldn't see their beams, only gradually

like we do, they would see it exactly
what the crew the stationary ships sees.

Light beams rapidly fleeing their
headlights at the speed of light

just as if they were moving at all. And
here's why. Let's say this distance

is a light second. The distance light
travels in one second. Which is

Now, after one of our seconds, sure enough,

both beams will have traveled a light
second. But the crew of the moving ship

measures light speed to be the same as us.

But how does that make sense?
I mean, light hasn't traveled a light second from

them yet. No problem. You see, what they
measure a light second to be

they wouldn't agree that a second has
passed yet either. Because, of course, to

time is slower for them. They count one
second finishing later then we do,

at which point their light has, indeed,
traveled one of their light seconds

about time and space, but those
disagreements with always conspire

to make sure they agree on one thing.
The speed of light.

at the speed of light? Well, the only
thing that could do that would be a

massless vehicle. So, fine, let's assume
that we can build one.

a tiny tiny bit ahead of it. No matter how short

it thought a meter was. No matter how long
it thought a second was.

It would never register light ever moving ahead of it.

It would say that light was stationary.
It would not agree that light travelled

at the speed of light. Right? Not really.

You see, at the speed of light there is nothing

to see. Not because there's nothing to
see but because there is nothing

As we have seen, as an object's velocity approaches

"C", time for everything around it approaches

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Would Headlights Work at Light Speed?

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