Would Headlights Work at Light Speed?


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 would your headlights just stay dark? 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 speed plus the speed of your car. No, that doesn’t sound right. None of these
answers sound right because, of course, there is no answer. A car cannot travel at the speed of light. Nothing that has mass can. 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 out of light. Okay. 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 and about whether or not we are real. In order to see what I mean we need to
talk about “C”. The speed of light. It is Constant. As long as you aren’t
accelarating, you can move as fast or slow or in whatever direction you want and you will still always see light moving at light speed. Even when light appears to slow
down, as it passes through different materials, 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 measurements of you change. When you move, everything not
moving with you appears to you to be shortened 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 we usually travel at. 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% the entire Earth would only appear to be 70 meters deep. Our whole planet. 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 at 99 percent the speed of light. The Near Light Speed Ship would be
flattened in the direction of its travel to us, 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 from behind. 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 gaining on them 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 299,792,458 meters. 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 is shorter than what we measure. And they wouldn’t agree that a second has
passed yet either. Because, of course, to us 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 from them. Observers will often disagree about time and space, but those
disagreements with always conspire to make sure they agree on one thing.
The speed of light. It is always the same for everyone. But what if you were travelling 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. Such a vehicle would travel with light. Light would never even pull 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 to do any seeing. As we have seen, as an object’s velocity approaches “C”, time for everything around it approaches a standstill. An object traveling very very very very very very
near the speed of light could travel for billions of our years before a single second past for it. But a massless vehicle, travelling at the speed of light, could travel forever before an instant even began for it. It experiences no time. And it would have no time to do anything. Certainly no time to turn on its headlights. The concept of time doesn’t even really apply. A massless vehicle couldn’t even
have its headlights on before it hits “C”, because object with no
mass must always travel at “C”. Such an object would never have a before. Its origin, its journey and its destination are simultaneous for it. A billion light year trip from a distant quasar might take a photon a billion years to us. But it literally takes no time for the photon. And to the photon, the
distance to us from that quasar is literally nothing. Photons are how we see. How we know anything
about our place in the universe, and the energy they bring our planet from the Sun is responsible for nearly all life on Earth. But despite that list
of accomplishments, they don’t think much of themselves. In fact, as far as they’re concerned, they don’t even exist. Outside observers, of course, see them and would measure them to be
moving along at the speed of light with nothing passing or gaining on them.
So if you were moving at the speed of light, you’d have to be massless, like a photon, and you wouldn’t notice anything, because to
you there would be nothing, and no time to notice it. Other people
would see you doing nothing and you would be unaware of yourself. You
could never turn on headlights because you would feel exactly like you
felt before you were conceived. But why is the speed of light what it is? I mean, this is how far light travels in a second. Could it also travel this far, or this far, or this far?
Could we conceive of a universe where light traveled that quickly? Yeah, easily. So then, why is it that the universe we live in is only one of these ways? Why are the laws of physics what they are? Instead of some other way they could be. Well, there are a lot of theories, but so
far we’re not exactly sure how to test any of them, because we are stuck in this universe and don’t yet know how to
create universes of our own for experiments. But perhaps there is
something we have yet to discover that compels reality to be this way, and only this way. Or, perhaps, nothing compels it to be this
way but instead there’s a multiverse. Every single possible universe exists. Some of them collapsed
immediately, some of them are empty and dark, some of them involve you watching this very video but Earth has two Suns. For those of you, in that universe
watching, that was probably very confusing what I just say because your Earth does have two Suns.
But the point is, the multiverse would be a pretty elegant explanation.
Or maybe, universes are born inside black holes. Universes whose physical laws are only
slightly different from the universe that gave birth to it. In this way, universes could replicate
according to natural selection. Universes that are more fit for creating black holes would then have more baby universes, making universes that support black
holes more common, like maybe the one that we’re in. And that’s
pretty lucky because universes that support black holes support Suns, and us. Or – and here’s my favorite theory – maybe we’re just living in a simulation.
And someone or something else programmed it up. That sounds pretty sci-fi. Sure. But I like how Julian Baggini puts it in “The Pig That Wants to Be Eaten”.
If you assume, that at some point in time, virtual reality could become good enough
that even its own inhabitants didn’t know they were in a simulation,
and if you assume creating such simulations would be way easier than creating real
flesh-and-blood creatures that require an entire universe
and billions of years. Well, then it’s pretty easy to conclude that
many many many many more simulated, faked beings could be created than real ones. Say, 999 fake ones for every one real one. What’s more likely?
That you’re part of the 0.1% that are real, or that you are part the 99.9% who think they’re real but aren’t. Perhaps, we live in a simulation
created by some other intelligent species. John Gribbin, however, points out one possible way to
dismiss this idea: irrational numbers. Like the square root of 2 or Pi. These numbers don’t end. I mean, they contain a never-ending, never repeating sequence of digits, which
would mean that whoever programmed this universe could fit in all of, say, Pi. So, if in our tireless pursuit of
calculating more and more and more digits of Pi, we ever run into an endlessly repeating series or the end, that could be a pretty good sign that we live in a simulation. A universe that is not real. But so far we haven’t found that and we
don’t think that we will. So, thank you irrational numbers, for keeping it real. And as always, thanks for watching.

100 Replies to “Would Headlights Work at Light Speed?”

  1. Two things I’ve learned:

    1. Irrational numbers keep it real!
    2. My fridge is watching me!

    I knew I wasn’t paranoid when I said my fridge and my toaster were conspiring against me!

  2. Where in all of the universe is velocity = zero? Right where you are. Even if you’r in a car, airplane, spacecraft. Think about it.

  3. Wait the light travels at light speed. The sun expells light, but apparently the light from the sun takes 8 mins to reach earth. Why doesn’t light from the sun come faster

  4. Muhammad Ali once said that he was so fast that when he turned the lights out in his bedroom, he would be in bed before the room got dark. Now that's fast.

  5. That moment when you are walking into a fridge and you experience time dilation due to a black hole in your fridge. And that your room is warped and the clocks go back in time

  6. What about 51% the speed of light in the opposite direction of another object going 51% the speed of light so relative to each other its 102%. The two objects would not receive photons from each other thus would not be seen even though its there. Perhaps the photons do reach but the wave lengths are so stretched that it appears black thus not being seen. But you know its there and you call it dark energy.

  7. Multi verse is an improbability due to lack of "dark flow" observation. which was one of the hypothesized conditions that should exist as a tell tale sign for another universe.

  8. I really wish that science communicators, and YouTube channels, like this otherwise excellent channel (for laypersons) that deal in such, would stop talking about the speed of light as some kind of cosmic speed limit… And, instead, talk in terms of the ''speed' of causality.' The speed that Light travels at is an effect, not a cause.

    Light, being massless, must travel at such a speed… The speed at which cause and effect propagates. (And MUST do so!)

  9. if we live in a simulation… it sucks! At least for me. they could have at least made an interesting simulation with magic and dragons and aliens… instead we get this boring one where everything is neatly explained and barely any true mystery remains in the world. I kinda wish I was born in the past when science hadn't explained away all the mysteries and there was still a sense of wonder to the world. now it just seems so… predictable and bland.

  10. Hey vsauce. Ive been wondering for a long time on this subject. Every video and explanation i encounter were always that of "forward" headlight. What about the back headlight ?. If i turn on back light when i travel at C, does the light travel at 2C at my point of view. The time dilation explanation doesnt make sense for backlight to me. I need some explanation

  11. wow, your intro was like 3/4 of the questions I thought about before i clicked on this video! nice! even explained the red shift question i asked myself

  12. …but if they'd work, then I guess all the energy would be concentrated into one location and it would "burn" a hole into space-time, leading to a creation of a black hole.

  13. Damn he should've said "your Earth has one sun…" And "that was very confusing for you because your Earth does have one sun" lost opportunity.

  14. If you think about it, if you were to be moving at the speed of light, you woukd feel your body as usual, but the only thing you would see is the thing you saw the instant you reached soeed of light. You would think you lagged out.

  15. Beginning: Would headlights work at light speed?
    End: We live in a simulation, there are multiple universes, irrational numbers are the key

  16. irrational numbers wouldn't disprove the simulation hypothesis, would they? I could image a program that proceduraly generates an irrational value. A value that is both predetermined yet infinitely complex. A number that could be fit into a few lines of code.

  17. What if the creators of the simulation want us to calculate that Pi is never ending and non recurring???!!
    What if they planned it all like we're a particular generation in machine learning and they're experimenting stuff on us..!?

  18. Yes there is a Creator Who created everything and all the laws of universe, He is Allah there is nothing like Him

  19. Humans: Gets close to finding the last digit of Pi.
    Programmers: Pauses simulation. Gives simulation new software update. Plays simulation.
    Human: Wow there is still no last digit or repetition. Thanks irrational numbers for proving we're real.

  20. Wait, your Earth does only has one sun?
    Man, watching YouTube made in another universe sure is interesting.

  21. What if irrational numbers are only calculated dynamically? We wouldn't notice lag from large calculations since our minds would be lagging as well.

  22. 12:00
    Me :- HIGHEST BAR EVER DROPPED IN THE HISTORY OF MANKIND …… idk why but i get pretty excited about these stuff😅😅

  23. I disagree with the irrational number argument, due to the fact that you're not measuring any property of the physical world in order to determine its value, and you don't have to know every digit to realise that that number of digits is infinite. You are using an abstract idea to determine its value.

    The simulation itself doesn't exist, it cannot exist, only the physical world in which the simulation is created exists. Any truly conscious being experiencing this simulation would themselves either be derived from the physical world and be immersed in this simulated environment, or they are the very machines which run the simulation. In other words they are the very entities that are experiencing the very simulation that they themselves are running.

  24. The speed of light is not constant, the velocity of light is influenced by what medium it is passing through. the C in E=MC^2 is a constant defined as the velocity of light through a vacuum. So for clarity Lene Vestergaard Hau of Harvard University has stopped light passing through a bose-einstein-condensate. Source: https://www.seas.harvard.edu/haulab/

  25. Great video!. But.. the right question you asked is why is the speed of light what it is and not some other number.. but then you went off on one and went asking about all laws of physics instead of focussing on that one question. Perhaps some ADD pills ?

  26. some scientist (astronomers) found objects (heavenly) travelling faster than the speed of light
    i don't know if this news is hoax..

  27. There are only 2 facts – 1 – you are alive (AKA "I think, therefore I am") – 2 – you are going to die. Death defines the universe as real.

  28. I'd like to travel near the speed of light for just a few moments so I could slow back down and watch vsauce's head in a jar doing a holovideo in the year 4000.

  29. well if there's an infinite number of uninerses and each can have different laws of physics then you could come up with an infinite amount of ideas for a universe and there would be an infinite amount of that universe, even with our own there are an infinite amount that are exactly like us every second

  30. So what if we built a vehicle that has mass, that goes only 100m/s less than light speed? Isn’t that theoretically possible?

  31. I always wondered. Why cant you go faster than the speed of light ? Space is nothing, what is your speed measured from ? As opposed to earth ? Since space is nothing speed would be relatively meaningless to anything other than the other objects in space …

  32. I kinda wish the line had been
    “And maybe there’s a universe where the earth, only has one sun. For those of you watching in that universe…”

  33. If a different version of this video existed that version of Michael would know there were 2 suns and would say “the version of earth with 1 sun”

  34. 4:07 what if the ship is moving backwards? (or the headlight is pointing backwards for that matter). It's a question I always had about relativity, and I never found an answer

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