Science fiction authors and readers dream of travelling at the speed of light, but Einstein tells us we can’t. You might think that’s an arbitrary rule, but [FloatHeadPhysics] shows a different way to think about it. Based on a book he’s been reading, “Relativity Visualized,” he provides a graphic argument for relativity that you can see in the video below.
The argument starts off by explaining how a three-dimensional object might appear in a two-dimensional world. In this world, everything is climbing in the hidden height dimension at the exact same speed.
Our 2D friends, of course, can only see the shadow of the 3D object so if it is staying in one place on the table surface, the object never seems to move. However, just as we can measure time with a clock, the flat beings could devise a way to measure height. They would see that the object was moving “through height” at the fixed speed.
Now suppose the object turns a bit and is moving at, say, a 45 degree angle relative to the table top. Now the shadow moves and the “clock speed” measuring the height starts moving more slowly. If the object moves totally parallel to the surface, the shadow moves at the fixed speed and the clock speed shadow doesn’t move at all.
This neatly explains time dilation and length contraction. It also shows that the speed of light isn’t necessarily a rule. It is simply that everything in the observable universe is moving at the speed of light and how moving through space affects it.
Doesn’t make sense? Watch the video and it will. Pretty heady stuff. We love how passionate [FloatHeadPhysics] gets about the topic. If you prefer a funnier approach, turn to the BBC. Or, if you like the hands-on approach, build a cloud chamber and measure some muons.
Since is movement relative to a fixed point and the fixed point is a matter of definition, can’t we define the fixed point to a photon? Would that make me moving at the speed of light ?
Massless particles move at the speed of light relative to everything else in all inertial reference frames, a photon as the reference frame is entirely nonsensical in modern physics.
Exactly. No matter how fast you are going or in which direction, the speed of a photon relative to you is the same.
How do you stop when your traveling at the speed of light?
Considering that all time occupies a single point at that speed, “stop” doesn’t really have much meaning for a photon. From its frame of reference at least.
I haven’t looked into it much, but I would assume that while traveling at the speed of light, you are still affected by natural forces of gravity, friction etc. So even just by colliding with a single piece of space dust, you would transfer some (a very minute amount, but still some) of your kinetic energy to the dust, slowing you down a bit, just enough to bring you out of “speed of light stasis” so you can act on yourself (or a spaceship if that’s what you’re in).
I’m perplexed by the color of light. Since photons are moving at the speed of light, their “clock” as observed by us is not moving. So, what is waving in order to produce color? Our observation of a photon’s EM field is frozen in time. The relationship between frequency and wavelength depends on the passage of time, doesn’t it? Also, the explanation above for everything traveling at the speed of light is cute but left out the impact of velocity on mass.
(undergrad relativity physics only, this analogy probably needs refining)
Cut a sine wave out of paper, then set it so its long axis is orthogonal to some vertical reference (“y” on “intensity” axis). Slide the fixed nine wave across the vertical axis moving in the direction of the wave’s long axis.
The sine wave is still “frozen in time” (you have already cut the paper), but the bulk of it is moving by.
One seeming error you stated is that our observations are frozen in time. If I went to Andromeda at the speed of light (classical, known physics only) it would take zero time to get there – as measured by my personal wristwatch. Andromedeans and Earthlings would watch me travel for however many years Andromeda is light-years away from us. ‘Interstellar’ really nailed this concept.
The answer to “what is waving” is quantum-mechanical, and again outside my expertise. My limited understanding is that a photon is a variation in the electromagnetic field, propagating like waves on a lake, until it “couples to” (“hits”, if you prefer) something. The energy of a photon is in the form of a wave of amplitude changes of length between successive crests of, say, 430nm. So to capture that energy (“feel it”) something needs to “be jigglable” by a wave with , wavelength of 430nm.
Our eyes have bits which can be jiggled, and the rest is anatomy/biology/psychology.
You can even dispense with the feeling as if a photon should be a physical thing you can grab and that fits through holes by instead sticking with the thinking of it as information about a field. Because then, the original light may have come from wiggling an electron in a ruby laser for instance. The ruby laser could even just be a fancy way to wiggle a bunch of electrons in similar ways at the same time.
We wiggle free electrons different ways to make microwaves sometimes. If we had a way to wiggle one just right, we could make visible light the same color as the ruby did. Maybe we’d be wiggling it similar to how they do in the crystal, idk. But the information on what we did would propagate as and at the speed of light. The electron’s field extends to infinity, even though it still falls off with distance as usual. And for the most part you can ignore almost every charge because you can assume it’s not doing anything related to what you’re doing.
But as the packet of information about your wiggling electron got near some matter, the charged particles in the matter can experience a disturbance in the force. Well, the force that is between them and the original electron, anyway. If the wiggle is slow, even a small force (from being distant) can still accelerate some bits around eventually. On the other hand there’s not much kick, so it may not do much until quite a bit of this has happened. If it’s fast, it has to get close before there’s enough force to disturb them as much, but once it does they’ll be properly disturbed. Well, a faster wiggle is a higher energy photon, a bluer color, etc. So if the matter is close enough compared to the speed of the wiggle, then an interaction can occur. Maybe that’s some light going through some glass. All the charges in the glass are not doing anything super crazy, so the main thing that happens apart from some dispersion is that the light “slows down”. That’s because the original wiggle plus all the responding wiggles from the charges in the glass equals a slightly delayed version of the original wiggle. It’s probably a weird thing to say, but you could say the original wave doesn’t exist, but that almost all its information propagates in the glass such that one that’s approximately the same thing comes out on the other side, with some specifics going into the theory of optics. For instance a wiggle in one direction could move faster than in the other direction, if there’s a crystal that’s structured that way like calcite instead of glass. That’s because the responding wiggle of the “clear” substance is not identical in both axes. If the substance is opaque, then the photon’s interaction with the charges in the matter dumps its energy into them. If you have some of both you have some of both. Maybe sometimes the wiggle’s direction changes but the energy isn’t dumped. Other times it produces a counter-reaction also without dumping the energy, so the counter reaction goes backwards like a bouncing ball. Or the packet knocks an electron loose in a solar panel or a glow in the dark thing. It can do all sorts of stuff.
Oh, and holes. So the holes work as if when your wiggle is slow enough, then the size of the hole might be small enough compared to the radius of significant interaction that the walls of the hole can interact with the wiggle, and then the interaction produces the effects we’re used to.
At least this is my current mental image, having not studied this stuff in some time.
I feel that one major missed idea is that time is not a constant.
Speed of light has an understanding of distance and time. But time is relative to gravity as it is warping space. More gravity (high mass) and slower flow of time. No gravity is fastest flow of time.
Which means when light is traveling it is subject to the changes of how time is flowing. If 2 our seconds happens in 1 second for time or 1 second is 2 seconds of time it will change how far it is going in any measure of time.
The universe expands and shrinks based on potential energy. As the universe is forming there are more and more possibilities opening up.
The balloon of our universe expands. Till the total potential of the universe has balanced with the choices that are now limiting the options available.
In short. The potential possibilities are like voltage. The greater the options. The higher the voltage. As voltage starts moving in a direction based on choice it lowers the total potential but there is an increase in amperage and increase in magnetic fields.
Once all potential (choices) is exhausted. There is no more voltage. And no additional amperage.
Once it all returns to start point due to magnetics causing a motion of forces. It will all gather again and cause a new big bang.
Real👍
No, distance is what is relative due to gravity.
Time is relative due to velocity.
You can, but remember that, then, all the universe (including you) will “look” as a single, 2D plane, without dimension in the direction of movement. That’s why, from the perspective of the photon, it can arrive at any point of the universe in no time.
Ops… this was an answer for 3eggert.
@Rastersoft said: “Ops… this was an answer for 3eggert.”
You are mired in WordPress Jetpack, therefore in order to communicate effectively you MUST explicitly state WHO you are replying to EACH AND EVERY TIME you make a reply – otherwise the end result just melts into irreversible CHAOS! Welcome to the Hack-a-Day Comment System, more fun than a barrel of Monkeys.
Mind blown! The next question where does everything travel to at the speed of light?
And where does the infinite energy come from to sustain speed of light? The universe would have to shrink, not expand.
Also you can only have speed if something stays behind, that would also mean infinite friction happening at that point.
You don’t need infinite energy to sustain that speed. You need energy to CHANGE the speed from the time dimension to the spacial ones, and vice-versa, and you need infinite energy to move ALL the celerity from the time dimension to the spatial ones.
The future.
What appears to be speeding up in space is actually just rotation of your 4D velocity into a more ‘spacey’ direction. You don’t notice the time dilation at ordinary speeds bc the necessary change in the 4D velocity direction is so small.
When we talk about the “speed” of something, doesn’t that measure the amount of “units of motion” per “units of time?” If so, how, exactly, do we measure the “speed through time?” Aren’t you then forced to acknowledge that there is a second, objective “clock” outside of time which is allowing you to measure the “velocity” of some object/particle through “time?” EG., the distance that the object in question moves through “time” (the 4th dimension of space) per unit of Time (the “true” clock which is used to measure all motion in 4th dimensional space/time.)
If this is wrong, can someone please explain to me how this actually works?
Consider a graph on paper. In this case movement in time is the Y axis, and ‘movement’ is the X axis.
Someone standing still goes up the Y axis 2 units. (This means they stood still for a certain amount of time).
Someone going quickly though, when they move the same 2 units, first moved 0.7 up, and 0.7 to the right (total length 1), and then 0.7 up and 0.7 back to the left (total length now 2). At this point they have arrived back where the first observer was, but have only gone ‘up’ 1.4. They only had 70% of the time pass for them.
Now we have a complication, because time is different for these two people, so the concept of speed becomes pretty blurry. Person A would say it took 2 units of time for person B to go shopping and come back, while Person B would say is too 1.4 units of time. Well, then, what is the fastest anyone can go?
A photon can move completely along X. It can go 1 unit to the right and 1 unit straight back. At this point the person standing still experience 2 units of y. That is the speed of light, 2 units of distance covered in 2 units of time. The light, by the way, hasn’t moved up the Y axis at all. It thinks no time has passed at all during it’s shopping trip.
This is how I think of it. Like a compass. If you’re heading north, you’re heading north – but not east. If you’re heading east, you’re not heading north. But if you’re travelling north-east – you’re making less progress north, and less progress east, but you are making progress in both ordinals.
So for spacetime – space is north and time is east. Most of us are going almost directly east – going through time at the speed of spacetime, but not making any good progress though space. Light is going directly north – travelling through space at the speed of spacetime, but not making any progress through time.
I think calling /c/ the speed of light does it a disservice. Think of it as the speed of spacetime, and it starts making a lot more sense.
I’ve never (that I remember) seen “time” defined in any way that doesn’t imply time in the definition.
Only light can travel a speed of light
and gravitational waves, I think
It’s actually the speed of causality.
Think of spacetime as two axes. One space, one time. Speed is going straight down the space axis, crossing vast distances but experiencing no time. We’re going almost directly down the time axis, experiencing the full passage of time, but crossing no significant distance.
And this is why speed (across space) dilates time – the more you’re crossing space, the more your vector is angling away from that time axis, and you experience less passage of time.
I am travelling at the speed of light – but I’m travelling through time, not space.
Say I’m currently traveling at the speed of light on a specific vector. If I run in the same direction, will I travel faster than the speed of light?
Nope. But not even the first part could happen anyway
How do you explain the concept that as an object approaches the speed of light, its observed mass becomes infinitely large?
Energy is mass. Give something more energy and its mass very slightly increases. Approaching the speed of light is a LOT of energy
JNX: NO. Light can travel at the speed of gravity, but only in a vacuum. Nothing, not even light, is faster than gravity.
We All are moving at the speed of light in the time dimension only.Space-time means time is a dimension. The conversion of time to distance is c = 186km/h (speed of light). I.E., 1 second per second.
Everything was fine and reasonable until he changed the pitch of the plane to justify length contraction. It is easy to visually understand, but I am not sure it makes actual sense. What is your take?
That felt a bit off to me, too, and started substitution it with a 1m^3 box in my head, which still felt a little weird because it seems to imply occupying a range of time in an instant. It works out better if you think of it in terms of slices of d/dt pointing in the direction of movement, YMMV depending on your comfort with calculus.
Already traveling at the speed of light. Hhmm. I think they mean we are to light as a drop of water is to an ocean
I dont think he got the 3d appearing to 2d right. Or I misunderstand wtf he’s saying
As long as we are not moving in space, we are travelling at the speed of light through time. As you go faster through space, your speed in the time dimension slows down. If you were to travel the speed of light through space, your speed through time would be zero. In all cases, your total speed through SpaceTime is c.
What does your first sentence mean?! Speed is distance/time. In fact no time passes in the rest frame of an on-shell photon and it never travels any distance in its own frame. The ratio of these two zeros remains c.
I think there is a lot of confusion in these comments w.r.t. speed vs. velocity.
This is confused. The leap to ‘space-time’ by analogy to a 2D plus ‘Newtonian’ time is strange at best, flawed probably. What is a constant speed in a ‘spacetime’. You switched from a ticking clock and 2 spatial dimensions adding in quadrature to somehow including the ticking clock in the sum. Certainly our spacetime can be a projection of a higher dimensioned space, that’s just maths. However this over simplified analogy does not seem a good way to explain the metric of spacetime.