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The speed of light

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Submitted ⁨⁨2⁩ ⁨days⁩ ago⁩ by ⁨fossilesque@mander.xyz⁩ to ⁨science_memes@mander.xyz⁩

https://mander.xyz/pictrs/image/f8f5e5b9-9fc2-4812-8062-2fb4fc708f11.jpeg

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  • cannedtuna@lemmy.world ⁨2⁩ ⁨days⁩ ago

    Image

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    • whotookkarl@lemmy.dbzer0.com ⁨2⁩ ⁨days⁩ ago

      When sailing boats pushed for speed they ended up hitting an unexpected speed barrier. As you increase velocity the break wave created by the bow of the ship elongates until the length of the ship is at 1 wavelength, then the hull drag prevents further acceleration. For a 50 meter ship it’s about 17 knots. You can get much faster lifting the boat from the water as you gain speed with an underwater wing, the current max speed was set 47 years ago at ~276 knots. But that’s only because they can remove the hull from the high drag environment and is extremely dangerous to attempt to break. The speed of light is nothing like that because spacetime itself can stretch and squish, I just wanted to talk about boats for a bit.

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      • icelimit@lemmy.ml ⁨2⁩ ⁨days⁩ ago

        So you’re saying, we need to lift the spaceship out from space/time.

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      • cannedtuna@lemmy.world ⁨2⁩ ⁨days⁩ ago

        Still very interesting

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      • Sylvartas@lemmy.dbzer0.com ⁨2⁩ ⁨days⁩ ago

        I’m not even mad because now I get why and how these competition multihull boats basically fly above water while keeping like 1% of the boat in water

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      • kuberoot@discuss.tchncs.de ⁨1⁩ ⁨day⁩ ago

        I love this because this feels like something the 10th doctor would say to confused daleks while stalling

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      • NocturnalMorning@lemmy.world ⁨1⁩ ⁨day⁩ ago

        I don’t like being deceived John! Tell me more about boats!

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    • FuglyDuck@lemmy.world ⁨2⁩ ⁨days⁩ ago

      You have two observers, moving directly opposite each other.

      Each has a flashlight pointing back at the other.

      The speed of the light from those torched is the same for both observers.

      (Instead the light would be red-shifted.)

      Add a third observer, stationary to one and moving towards the other. As the third observer passes that observer, the speed of light from their flashlight never changes. (Instead it would go from being blue shifted to red shifted.)

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      • scbasteve@lemmy.world ⁨2⁩ ⁨days⁩ ago

        This adds substantially more questions than it answers.

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    • tuxiqae@lemmy.dbzer0.com ⁨2⁩ ⁨days⁩ ago

      The fact that this gif has a brief pause between the “ex” and the “explain” really irks me

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      • cannedtuna@lemmy.world ⁨2⁩ ⁨days⁩ ago

        It’s there to convey the line’s intonation.

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      • MJKee9@lemmy.world ⁨2⁩ ⁨days⁩ ago

        Ex…Term…Ah…Nate!!!

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    • umbrella@lemmy.ml ⁨1⁩ ⁨day⁩ ago

      spacetime ia relative

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    • rumba@lemmy.zip ⁨1⁩ ⁨day⁩ ago

      The simplest explanation I know: Nothing can travel faster than the speed of light. If you ever end up with something that makes the speed of light change, it’s actually time that changes.

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  • 5too@lemmy.world ⁨2⁩ ⁨days⁩ ago

    A bit late to the party, but I’ll try anyway!

    So, first, speed is distance over time. Miles per second, kilometers per hour, whatever.

    Consider a person rocketing by a planet in a little spaceship at a good fraction of the speed of light. To amuse themselves, they’re bouncing a ball between two paddles on opposite walls of their craft. The ball describes a path like:

    O--------O

    –O----O

    -----O

    Of course, to a person on a planet they’re blasting past, the path looks different - the ship moves a long way between each bounce, so they see:

    O----------------------------------O

    -------O------------------O

    ----------------O

    The thing is, both of these are correct from each point of view - from each reference frame. For the shipboard person, the ball moves the width of the ship, and for the planetside person, it covers the distance the ship traveled in the bounce (plus some for the width).

    Now, swap the ball for a photon, which always moves at the same speed. The distance the photon travels from the two points of view - the two reference frames - is different, so the time component of the photon’s speed must change as well for the speed to stay the same! Each side sees the photon moving at the same speed, despite the difference in distance - which means each must have a different measurement of the time involved!

    So, time is compressed on the spaceship relative to the planet - from the ship, the planetside observer is moving very fast, while to the planetside observer, the space pilot is moving in slow motion.

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    • MJKee9@lemmy.world ⁨2⁩ ⁨days⁩ ago

      And that is what is meant by time dilation, and why Matthew Mcconaughey was younger than his grandkids. His balls took longer to bounce…

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      • zalgotext@sh.itjust.works ⁨1⁩ ⁨day⁩ ago

        Alright alright alright

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    • SoleInvictus@lemmy.blahaj.zone ⁨2⁩ ⁨days⁩ ago

      Great explanation, well done!

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      • 5too@lemmy.world ⁨1⁩ ⁨day⁩ ago

        Thanks! Wish I could remember where I saw an animation describing it this way - it was some educational software from the nineties, I’m pretty sure.

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    • musicalphysics@discuss.online ⁨1⁩ ⁨day⁩ ago

      In relativity both the planet and the ship see the other as moving slow. Not one fast the other slow.

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    • NocturnalMorning@lemmy.world ⁨1⁩ ⁨day⁩ ago

      I want to know why it works that way. I’m pretty sure we don’t actually know why that is a law of nature, just that it is. Some of these things I learned in physics I was frustrated that we can’t explain the why. We just kind of know this is what experiments tell us, and the math.

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      • starelfsc2@sh.itjust.works ⁨1⁩ ⁨day⁩ ago

        If you mean the relativity part, to my understanding space and time are basically a shared dimension, so the faster something is moving in space the slower it’s moving in time. Why it’s shared, I have no clue.

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    • MeThisGuy@feddit.nl ⁨2⁩ ⁨days⁩ ago

      Doppler who?

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      • 5too@lemmy.world ⁨1⁩ ⁨day⁩ ago

        Hah, I debated saying something about that, but decided that was a separate conversation

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    • ulterno@programming.dev ⁨2⁩ ⁨days⁩ ago

      So, even if I run very fast, I still don’t reach in time for the target people.
      Welp, I just have to start early.

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  • panda_abyss@lemmy.ca ⁨2⁩ ⁨days⁩ ago

    Okay, but what if I go the speed of light minus 1m/s and shine a flashlight, can I catch the photons?

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    • smiletolerantly@awful.systems ⁨2⁩ ⁨days⁩ ago

      No

      That’s not a physics statement btw. I just think that you, personally, are too slow to be able to do that. Offense intended.

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      • a_non_monotonic_function@lemmy.world ⁨2⁩ ⁨days⁩ ago

        That may seem harsh to the casual reader, but it’s 100% true in this case.

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    • OwOarchist@pawb.social ⁨2⁩ ⁨days⁩ ago

      You can catch the photons just fine without needing to go absurdly fast. Just put your hand in front of the flashlight beam, and you’ll catch lots of them.

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      • homesweethomeMrL@lemmy.world ⁨2⁩ ⁨days⁩ ago

        Physicists hate this one weird trick

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      • Evil_Shrubbery@thelemmy.club ⁨2⁩ ⁨days⁩ ago

        without needing to go absurdly fast

        … I would actually argue that for a human catching anything at e-1m/s is deadly.

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    • nexguy@lemmy.world ⁨2⁩ ⁨days⁩ ago

      Light ALWAYS travels away from you at the speed of light no matter how fast you and your flashlight are going. Something has to give and that is time. It may look to outside observers, not traveling that fast along with you, that light is going 1 m/s faster than you… but you would also appear to be moving in super slow motion trying to reach out for the beam. The faster you go the slower time moves for you.

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      • not_IO@lemmy.blahaj.zone ⁨1⁩ ⁨day⁩ ago

        no i think the light would indeed just travel 1m/s away for them but it would be very blueshifted, they could never catch it as in catching up to it because they can’t reach the speed of light instead their mass gets more and more

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    • pomegranatefern@sh.itjust.works ⁨2⁩ ⁨days⁩ ago

      Nope. In your frame of reference, they will still be moving at the speed of light.

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    • webghost0101@sopuli.xyz ⁨2⁩ ⁨days⁩ ago

      I think the answer is that you are only traveling at almost light speed from reference frame of your start position.

      The light of the lamp travels at light speed from your own reference speed which to you in a vacuum is 0.

      Anyone correct if wrong please?

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      • BluJay320@lemmy.blahaj.zone ⁨2⁩ ⁨days⁩ ago

        Correct. Physics gets really, really weird at relativistic speeds. Something to keep in mind is that the speed of light isn’t actually the speed of light itself, but rather the speed of causality - the universe’s hard limit at which any interactions can occur. Even if you are traveling at .99c from a certain reference frame, space time itself warps in such a way that your measurements still determine that light travels away from you at 1c

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      • thisbenzingring@lemmy.today ⁨2⁩ ⁨days⁩ ago

        Any observations wouldn’t see anything but the whole light

        I believe this is explained by Einstein in his example of the train in the Theory of Relativity

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    • airbreather@lemmy.world ⁨2⁩ ⁨days⁩ ago

      You’re already traveling at the speed of light minus 1m/s relative to a reference frame that’s traveling away from you at that speed.

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      • panda_abyss@lemmy.ca ⁨2⁩ ⁨days⁩ ago

        Wow, and I’m in my pyjamas while doing it

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    • ZombieCyborgFromOuterSpace@piefed.ca ⁨2⁩ ⁨days⁩ ago

      No. Ever heard of the doppler effect?

      Light behaves like a wave. But instead of hearing sound in a higher/slower pitch relative to the source, you’d be seeing a different color.

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    • merc@sh.itjust.works ⁨2⁩ ⁨days⁩ ago

      If you’re going at the speed of light minus 1 m/s and you turn on a flashlight, the beam emitted by the flashlight will be travelling at the speed of light, according to your measurements. Time passes slower the faster you travel.

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  • whitedovebooks@lemmy.world ⁨2⁩ ⁨days⁩ ago

    If you were on a train that was travelling at 60 mph and you threw a ball (inside the train) and the ball was travelling at 10 mph (inside the train), then the ball would objectively be travelling at 70 mph. Any observer (outside the train) would be able to understand why it looks like 10 mph inside the train and 70 mph outside the train.

    Are you with me?

    Okay, so the same thing does not happen with light! If you turn on a flashlight (inside the train), the light would be travelling at 670,616,629 mph regardless of whether the train was stationary or moving. So an observer outside the train would see the light travelling at the same speed as an observer inside the train. Even if the train was some supersonic invention from the future, the light inside the train would still be travelling at 670,616,629 mph - not 670,616,629 mph plus the speed of the train. And both inside and outside the train, observers would see the light as travelling at that speed. That’s the big thing to get hold of!

    How can this possibly be the case?

    The answer is that time itself actually slows down when we are in motion. At low speeds, the effect is negligible, but the closer we get to the speed of light, the more the effect becomes observeable, until, when we are travelling at the speed of light, time stands still. If we were able to go faster than the speed of light, we would be travelling backwards through time.

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    • 87Six@lemmy.zip ⁨2⁩ ⁨days⁩ ago

      Thanks for fucking up my mind so I can’t get anything done at work for the rest of the day lol

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      • Zink@programming.dev ⁨1⁩ ⁨day⁩ ago

        Oh it gets even weirder than that.

        One observer can see two events happen simultaneously while another sees them happen at different times.

        And EVEN WORSE than that, thanks to length contraction at relativistic speeds, you could have one observer think that a train is contained entirely within a tunnel, but another observer sees the train sticking out both ends of the tunnel at the same time without ever fitting entirely within it.

        and/or: One observer objectively masures that object A is longer than object B, while another observer objectively measures that object B is longer than object A.

        The two observers are not just hanging out together, of course. They are moving ridiculously fast relative to one another.

        The speed of causality is a hell of a drug.

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    • UnrepententProcrastinator@lemmy.ca ⁨2⁩ ⁨days⁩ ago

      So it’s woven with space?

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      • Meruten@lemmy.dbzer0.com ⁨2⁩ ⁨days⁩ ago

        They are one and the same.

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      • Luna@ani.social ⁨2⁩ ⁨days⁩ ago

        Yup moving through space faster means moving through time slower. Kinda like if you were traveling at a constant speed through a 2d grid, if you make your vertical speed faster, your horizontal speed would be slower, except replace the grid with spacetime where we’re pretty much always traveling through time at 1c

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    • YiddishMcSquidish@lemmy.today ⁨1⁩ ⁨day⁩ ago

      I remember learning that if a quasar is spinning fast enough, then the radio waves inside are theoretically traveling faster than light. Which means that some of the star’s mass is actually experiencing time in reverse, until they breach the corona.

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      • rumba@lemmy.zip ⁨1⁩ ⁨day⁩ ago

        That’s a super interesting idea, but I don’t think it’s actually true. I think it’s in appearance only

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    • smeenz@lemmy.nz ⁨1⁩ ⁨day⁩ ago

      The same thing does happen with light, in that your simple first example does need to consider relativity if you want to be exceptionally precise. It’s not correct to suggest these two scenarios are fundamentally different, where only one needs lorenz corrections. In truth, both scenarios do, its just that the correction is so insignificantly small for the first example that it can be left out without any significant change in the answer.

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  • LovableSidekick@lemmy.world ⁨1⁩ ⁨day⁩ ago

    The speed of light isn’t even really a speed.

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    • Spooge@lemmy.world ⁨1⁩ ⁨day⁩ ago

      But it’s also a speed

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      • KeenFlame@feddit.nu ⁨1⁩ ⁨day⁩ ago

        And also my furniture is a property of space itself

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      • minorkeys@sh.itjust.works ⁨1⁩ ⁨day⁩ ago

        It’s like it’s both space and time.

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  • yesman@lemmy.world ⁨2⁩ ⁨days⁩ ago

    I think it’s neat that Newton is taught first. As in: gravity is a function of mass. Because that works in so many scenarios.

    But then you learn that gravity bends light and that photons have no mass.

    So… Gravity isn’t a force, it’s more like going downhill… in the dimension of time.

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    • spacehulk@lemmy.zip ⁨2⁩ ⁨days⁩ ago

      If they have no mass, how do they push solar sails?

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      • ttayh@lemmy.zip ⁨2⁩ ⁨days⁩ ago

        They have momentum, but not mass (ignore the other explanation, like yes, E=sqrt(m0^2c^4 + (pc)^2), but so what? m0=0 for photons)

        As you can see, momentum, p, is p=E/c, and we know that the energy for light is proportional to its frequency, f, E=hf (h is Plank’s constant). So, p=hf/c. When light is absorbed by a material momentum (and energy) conservation apply and it imparts p onto the object. If light is reflected it imparts 2*p, showing this is left as an exercize to the reader

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      • BlackLaZoR@lemmy.world ⁨2⁩ ⁨days⁩ ago

        They have mass. Everything that has energy has mass. They don’t have inertial mass but it’s just part of the equation

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  • D_C@sh.itjust.works ⁨2⁩ ⁨days⁩ ago

    Ok, firstly I’m not very smart. Secondly I don’t understand the meme AND don’t understand the explanations in the comments.
    Can anyone actually dumb it down so a stupid person like me can understand it?

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    • 87Six@lemmy.zip ⁨2⁩ ⁨days⁩ ago

      Thing go slow - > speed act normal, speed add up between POV’s, speed make sense AF

      Thing light fast like - > speed act fucky wucky, speed don’t add up at all between POV’s, speed so fast make time fucky wucky too

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    • pomegranatefern@sh.itjust.works ⁨1⁩ ⁨day⁩ ago

      I suggest watching these videos from Float Head Physics. They’re just some of the clearest and most intuitive explanations of relativity I’ve seen, and any other explanation I give here would just be me attempting to paraphrase him.

      www.youtube.com/watch?v=Zkv8sW6y3sY www.youtube.com/watch?v=Vitf8YaVXhc

      He has a whole playlist on special relativity which is really insightful if you want an even deeper dive, as well as playlists on other things like general relativity and quantum mechanics, all of which are based on building intuition instead of starting with complicated math equations.

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      • D_C@sh.itjust.works ⁨1⁩ ⁨day⁩ ago

        Thank you for this.

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    • Zink@programming.dev ⁨1⁩ ⁨day⁩ ago

      For what it’s worth, there’s a damn good reason that Einstein’s name is associated with being super smart.

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    • GreenKnight23@lemmy.world ⁨2⁩ ⁨days⁩ ago

      you and two friends, Al and Be, are outside at night time. Al has a flashlight and flashes it at you and Be. Be is 20 feet away from Al, and you’re 20 feet behind Be.

            20ft         20ft
Al..........Be...........you
       r1          r2

      The photons from the light Al has hits Be first, so he sees it first. it took .03 seconds(r1) to reach Be.

      After that, the photons hit you and you can see it. it took .03 seconds(r2) to reach you from Be.

      They were both .03 seconds because you are equally apart and the speed of light is constant.

      so, how long did it take the light to reach you from AI?

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      • calcopiritus@lemmy.world ⁨2⁩ ⁨days⁩ ago

        In this example all 3 observers are in the same reference frame. That is, each of them are moving at the same speed. This is not what the meme is about. In this example the night from Al would reach you 0.06s after he lit it. Which is expected in Newtonian physics.

        The problem of the speed of light being the same for all observers is when they move at different speeds.

        The scenario is: Alice is inside a train moving at almost the speed of light, and Bob is outside it, looking at the train. Let’s set that light moves at 1m/s (for simplicity) and the wagon Alice is in is 1 meter long.

        Alice is at one end of the wagon, and turns a flashlight on. Alice will see the other side of the wagon illuminated after 2 seconds (since the light has to reach the other end and bounce back). Since the wagon is 1 meter long and the speed of light is 1m/s.

        However, when she turns the flashlight on, Bob is also looking. Let’s say that the train moves at 0.99m/s. In that case, after 1 second the light would have traveled 1 meter, but the wagon (and Alice) has traveled 0.99m, therefore the light is only 0.01m away from Alice.

        To summarize: after 1 second, in Alice’s frame of reference, the light has just touched the other side of the wagon. Meanwhile, in Bob’s reference frame, the light has only moved 0.01m away from Alice.

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      • Voroxpete@sh.itjust.works ⁨2⁩ ⁨days⁩ ago

        I’m not following how this explanation is supposed to help with their question. Like, what are you trying to get at here?

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      • rapchee@lemmy.world ⁨2⁩ ⁨days⁩ ago

        expecting klaxon sound … is it 0.06 s? assuming it’s a straight line

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  • LordCrom@lemmy.world ⁨2⁩ ⁨days⁩ ago

    And remember, a photon of light does not experience time. Time only applies to mass. When a photon is emitted traveling at the speed of light, it is eventually absorbed by something, eglight from the sun hitting your eye. The photon of ligjt, from the photon POV is emitted and absorbed in the same instance.

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    • heartSagan5@lemmy.zip ⁨1⁩ ⁨day⁩ ago

      But some of the photon is absorbed by the material it passes through called spectroscopy. I guess then it’s good it’s also a wave, as per the Light Slot Experiment.

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    • MeThisGuy@feddit.nl ⁨2⁩ ⁨days⁩ ago

      and electrons in a DC wire don’t travel, but push?
      and in AC they go both ways?
      I dunno electro physics was never my strong suit…

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  • Small_Quasar@lemmy.world ⁨2⁩ ⁨days⁩ ago

    Whilst we’re at it can someone explain;

    A) a photon travels at the speed of light because it is massless, right? But doesn’t E=mc² teach us that mass and energy are somewhat interchangeable? How can a photon have energy but no mass?

    B) I’m willing to accept it as fact when smarter people tell me that FTL is impossible because, amongst other things, it will break causality. It makes perfect sense to me that the universe needs to have some unbreakable rules for things to remain consistent. But I’ve never been able to grasp exactly why it would break causality.

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  • Zerush@lemmy.ml ⁨2⁩ ⁨days⁩ ago

    For a photon itself, time don’t exist, for a photon it is everywhere in the universe at the same time. Inly for an observer it need x time from A to B with a finite speed.

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  • stupidcasey@lemmy.world ⁨1⁩ ⁨day⁩ ago

    Not true, the universes speed varies and thus the speed of light varies with it.

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  • Kolanaki@pawb.social ⁨2⁩ ⁨days⁩ ago

    What if one observer is on one side of a medium that light passes through slower and anothet observer is on the other side? 🤔

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  • ace_garp@lemmy.world ⁨2⁩ ⁨days⁩ ago

    Real shit.

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