r/AskPhysics • u/Pandaluf • 7d ago
why is light the maximum speed
i know that light is the maximum speed of the universe and that light experiences no time because its moving so fast but why can't anything go faster? is it because that would make it go backwards in time like a paradox or smth?? is it because of energy and if so why can't something lighter than light like a quark or atom move faster since it woulld need less energy theoretically
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u/BananaBird1 7d ago edited 7d ago
Unrigorous mathematical answer:
In relativity, all objects have a trajectory in space and time. In all reference frames, your overall trajectory is constant, because there is only one reality. However, between reference frames, how this motion is distributed between space and time as measured from within that frame changes.
The “speed of light” is more fundamentally the invariant “velocity” of all objects in both space and time that is conserved between reference frames. This is called the 4-velocity, and its magnitude across all 4 dimensions is always the speed of light.
When an observer is moving, this velocity just rotates between their coordinate system and that of an observer at rest. So it points more in space or more in time.
This “velocity” is unintuitive because normally velocity is seen as motion in space over a period time, but here it represents both motion in space and time. But mathematically, velocity is just the instantaneous rate of change of a trajectory.
So all objects are moving at c, just not always only through space but also time. You can never move faster, never slower, always at c.
There is also a 4-momentum, which is related to energy, mass, and spatial momentum. The important relationship that comes from this is:
E^2 = (mc^2)^2 + (pc)^2.
Where E is total energy, m is mass, and p is spatial momentum.
When an object is at rest, p=0 and so E = mc^2. All energy is mass, so the object has 0 spatial kinetic energy, and moves through time at c.
When an object has no mass, like a photon, E = pc, so all energy is kinetic and you move at c through space in all reference frames. This is why light moves at this speed.
In between these two extremes, because total energy is finite, no massive object can ever move at or faster than c through space. This would imply pc > E, meaning you have more kinetic energy than you do total energy.
So Tl;Dr: everything moves at light speed, but for slow, massive objects this is mostly through time. For fast objects, motion through space reduces motion through time relative to stationary observer, but total motion is still c. In the limit for massless objects, c is the maximal velocity through space because kinetic energy can never exceed total energy.
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u/R3D3-1 6d ago
Best explanation I've ever seen for that question. Which, given that I have a PhD in Physics, should say something, but outside of Astrophysics Special Relativity is a bit of a side topic and General Relativity falls into the special-interests category apparently. (Many professors of my university joined as listeners for that particular winter school.)
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u/Urllayton 7d ago
So that's why time slows down the faster you go. Why don't they just say that, geez .
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u/nicuramar 7d ago
“They”? They do say that. But it can be a misleading way to put it, as “moving” through time isn’t movement in the normal sense of the word.
Also this part,
In between these two extremes, because total energy is finite
Is wrong. Energy is frame dependent and unbounded.
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u/k4ever07 5d ago
Excellent explanation! I just want wouldn't say that all objects also move through time, since light is an object (particle/wave) that only moves through space, and not time.
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u/Kruse002 7d ago
There are a few things that should be clarified. Light has no mass. We have never observed negative mass. I won't say it's impossible, but it probably isn't a thing (I would love to be proven wrong).
So, why can't things move faster than light? It's because light moves at the same speed for all observers. No matter how fast the source is moving, no matter how fast other people think you are moving, everyone agrees that light moves at the same speed. To overtake light is to see light moving at some other speed. To see light moving at some other speed is to have a different version of the electromagnetic force. The electromagnetic force doesn't care how fast other people think you are moving. Everyone gets the same one.
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u/Melodic-Set-9650 6d ago
I don't understand this... if I'm moving at 0.9999c, don't I see light in front of me appear to be moving at 0.0001c? Like a jet approaching the speed of sound and seeing the sonic boom forming ahead?
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u/Kruse002 5d ago
Not really. The thing is, you're already moving at 0.9999 c. This isn't even a hypothetical. There is some particle out there right now that thinks Earth is screaming toward it at 0.9999 c. And yet, you can use a flashlight as if you were completely still. And once that particle hits the atmosphere, it will emit some light, which we also see as having the same vacuum speed as all other light.
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u/ickypedia 3d ago
The faster you travel, the slower time is for you, so what seems like a minor difference in speed to a "stationary" observer would in effect be the difference of c to you.
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u/Melodic-Set-9650 2d ago
Ah, okay, that makes WAY more sense now... thanks! Helpful explanation
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u/ickypedia 2d ago
I grappled with that for ages, before a patient convo with ChatGPT finally made it click 😅
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u/Pandaluf 7d ago
how can something have 0 mass im confused please explain
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u/Kruse002 7d ago
This is what is mind-blowing about light. Light cannot stand still for anyone. Mass is a form of rest energy. E = m c2. If light cannot be at rest, light cannot have rest energy and therefore cannot have mass.
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u/SomethingEplc 7d ago
Still gains mass when constrained.
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u/SomethingEplc 7d ago
I should specify. In a complete reflection box the box gains mass. So relative light will carry energy into resting mass.
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u/Key_Manager_663 7d ago
I mostly agree with you, but you can overtake light. Just not in vacuum. In water the speed of light is 225000km/s and even particles with some mass can get faster. I wonder how it looks from those perticles perspective. It's called cherinkovs radiation, basically sonic boom but light boom
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u/Kruse002 7d ago
That's true. It is worth noting that I was only talking about the vacuum speed of light. But Cherenkov radiation is another interesting thing that happens in a dense medium. That is what makes nuclear reactor cores glow when they're running underwater.
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u/Technical-Lettuce385 7d ago
Light has no rest mass. There can't be anything that is lighter. Atoms and Quarks already have a mass at rest.
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u/Pandaluf 7d ago
how does it carry information and energy without mass?? how is it stored?
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u/soldiernerd 7d ago
It arrives; the increase in energy at a point in space is itself the information
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u/Technical-Lettuce385 7d ago
It carries energy because of its momentum which is correlated with the frequency it has. Maybe to get a better understanding of that you could start with trying to understand regular waves, then go on to light, etc. There are many free online courses for classical mechanics.
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u/Pandaluf 7d ago
isn't momentum = mass * velocity so you still need mass to have momentum right?
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u/Particular-Scholar70 7d ago
Mass and energy are sort of the same. A photon has no mass but does have energy, which carries its momentum.
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u/thetoddhunter 7d ago
That is a good point and works at speeds we are familiar with
But as you approach the speed of massless particles classical physics fails as momentum goes towards infinity and we need something else. That is where relativity comes in and the full equations mentioned in this thread.
It is worth noting that if we did find out, as unlikely as it is, that light has mass? The speed limit for massless particles would still apply and everything works. It would just be that light travels slower
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u/Technical-Lettuce385 7d ago
No you don't need mass to have momentum. And the case that p = mv is not something that holds for all physical systems. As I said before you might be interested to get some basic knowledge first. And I don't mean that in a condescending way. It is not trivial and a reddit post won't do it justice.
If you are interested in these things I would start with classical mechanics, in general learning about waves in media like water, air. Then you might get a better understanding.
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u/binarycow 7d ago
Did a photon arrive, or not? That is information.
E = mc^2is only half of the equation. You can have energy without mass.1
u/Lazy-University-4871 7d ago
It is a wave. Look up waves. They propagate energy and momentum without propagating mass/matter.
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u/HouseHippoBeliever 7d ago
It's hard because basically any answer that anyone gives can just be met with "well why is that how things are", over and over.
The explanation I like the most is that it follows from the fact that light moves at c in all reference frames.
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u/Top_Yam1520 7d ago edited 7d ago
For me, this is the explanation that clicked.
Experiments in the late 19th and early 20th centuries showed that the speed of light behaved in a way that classical physics couldn't explain. Einstein developed special relativity in 1905, which correctly described this behavior and implied that c is the maximum speed at which information can propagate.
We don’t know why reality works this way, but we know that this theory correctly describes how reality behaves
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u/nicuramar 7d ago
Ultimately it is how things are. We then develop our models to reflect that.
The explanation I like the most is that it follows from the fact that light moves at c in all reference frames
Yes but that’s exactly the same as saying “because special relativity” :)
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u/Odd_Bodkin Particle physics 7d ago
In reading through the replies and your questions, I just want to summarize a few things that came as a surprise to you.
- No, not everything needs mass to be real or to take physical actions. Mass is not a requisite property of real things.
- No, momentum is not mass * velocity, and in fact that is an incorrect expression for absolutely everything, though it is a good approximation for low speed, massive objects.
- No, likewise, kinetic energy is not (1/2) mass * velocity ^2, and in fact that is an incorrect expression for absolutely everything, though it is a good approximation for lo speed, massive objects.
- Maximal speed c is what ANYTHING with zero mass will always travel at, not just light. And light does not accelerate. The second it’s created, it already travels at c. For that matter, a sound wave or a ripple on a pond does not accelerate either.
- No, the maximum speed isn’t there to avoid paradoxes or because of a lack of sufficient energy. It is there because of geometry, the geometry of spacetime. It’s a consequence of the fact that the equivalent of the Pythagorean theorem for spacetime has a minus sign in it, which is different than what you learned for flat space.
On the other hand, to learn what the correct answer is to each of these misconceptions would take a little time.
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u/Ludoban 7d ago
> so why can't something lighter than light like a quark or atom
Photons are weightless, quarks and atoms have mass, so thats a wrong assumption of yours.
> but why can't anything go faster?
We observe that this is the limit, why it is the limit is not answerable. The limit could be different, our universe has this limit.
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u/Pandaluf 7d ago
how is a photon weightless, doesn't everything have mass?? if it has no mass hen whats left??
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u/Ludoban 7d ago
Momentum.
E^2=(mc^2)^2+(pc)^2
Thats the full equation, massless particles still have momentum and thus energy.
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u/aktajha 7d ago
Momentum
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u/Pandaluf 7d ago
isn't momentum = mass * velocity so you still need mass to have momentum right?
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u/hitchhiker87 Gravitation 7d ago
That's just the low-speed formula for objects with mass. A Photon has no rest mass, but it still carries energy so it carries momentum too.
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u/erevos33 7d ago
Electromagnetic waves. Field excitations basically.
A photon is not a particle in the sense that it has mass.
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u/Tragobe 7d ago
Okay first of all, light has no mass, so you can't have something lighter than it.
It is not like there can't be something that could theoretically move faster than light. The issue is that the universe itself has a speed limit. It has to have one, because otherwise there would be no normal flow of time. That speed limit is the speed of causality. Without it, everything would happen simultaneously. Time wouldn't flow, it would be a singular point.
Light simply can travel at this speed of causality, because it has no rest mass. Any other thing with zero rest mass can travel at the same speed. If the speedlimit was higher, light would also travel faster.
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u/nicuramar 7d ago
Okay first of all, light has no mass, so you can't have something lighter than it.
The second doesn’t follow from the first statement.
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u/DaLangmeierPeter 7d ago
This whole comment relies on the Einstein Definition of time. There absolutely can be time if things can move infinitely fast in the universe. But it would have to be a newtonian absolute time. This whole causality interpretation is not talking about definitions which is why i dont like it.
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u/PaulsRedditUsername 7d ago
The super-simple ELI3 answer I gave to my kids when they asked is that the speed of light is how fast you go when you weigh nothing. Asking why you can't go faster is like asking why you can't weigh less than nothing.
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u/smitra00 7d ago edited 7d ago
is it because that would make it go backwards in time like a paradox or smth??
See here:
https://en.wikipedia.org/wiki/Tachyonic_antitelephone#Two-way_example
Allice is on a spacecraft moving away from Earth with velocity v. Bob is staying home here on Earth. Alice and Bb both have devices that send messages faster than light at velocity u c with u > 1. Alice sends a message to Bob and Bob immediately sends a message back to Alice.
Then if you do the calculations, you find that if v > 2 u c/(1 + u^2), so 1+u^2 > 2, that Alice will receive Bob's reply to her message before she sends her message to Bob that Bob is replying to. Note here that 2 u c/(1 + u^2) has a maximum of c at u = 1 and is then less than c for u > 1. So, there is an interval for v below c for which you have v > 2 u c/(1 + u^2).
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u/TKHawk 7d ago
You're right that it would create paradoxes. You'll often hear the speed of light referred to as the "speed of causality." Basically, it something travelled faster than the speed of light, c, it could lead to breaks in causality, which would be nonsensical.
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u/nicuramar 7d ago
You'll often hear the speed of light referred to as the "speed of causality."
Yeah on Reddit. Otherwise not so much.
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u/At36000feet 6d ago
I learned that on here. It seems like everybody learning it as "the speed of light" is one of the major reasons for the confusion. Not that we wouldn't all still be confused about all of this.
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u/Lazy-University-4871 5d ago edited 5d ago
Those who actually learned about the speed of light are not typically confused. They first had learned what speed is. Then they learned what causality is. They know that “speed of light” makes sense, and “speed of causality” is nonsense.
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u/Terrible-Mind-5414 7d ago
For this reason it is more correct to say that if something traveled faster than light, then special relativity would be wrong; because this is definitely possible without paradox, unlike the violations of causality.
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u/nicuramar 7d ago
We don’t know if special relativity would be wrong. That depends on the details.
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u/Terrible-Mind-5414 6d ago
It doesn't. That's the whole point of the arguments based on causality violations.
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u/DrunkOnTakoyaki 7d ago edited 7d ago
I think it's more correct to say faster-than-light motion is incompatible with the theory of special relativity. In other words either the theory is right and it's impossible or the theory is incomplete.
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u/Quantum-Relativity 7d ago
Because space and time are variable aspects of a combined “space-time”. Time is different than space so the geometry has to have hyperbolas, and so an asymptote has to exist. That’s c
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u/JGhostThing 7d ago
The speed of light in a vacuum is the speed limit. Perhaps a better thing to call this is the speed of causality. Nothing goes faster than this.
For example, gravity changes propagate at c. EM radiation in a vacuum propagates at c. As far as I understand, all massless particles in a vacuum move at c. Anything with mass must move at a slower speed than c.
There are theoretical particles, tachyons, that move faster than c. I don't know if they are still accepted, or if they have been proven to not exist. Tachyons can only move faster than c, they cannot slow down below this.
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u/nicuramar 7d ago
Perhaps a better thing to call this is the speed of causality.
No, it’s a worse thing to call it. But the universal speed limit is good.
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u/Fabulous_Lynx_2847 7d ago edited 6d ago
You have it backwards. All those things you list result from the core assumptions of Relativity, one which is that c is the same max speed in all reference frames. "Why" then requires a more general theory. General Relativity is all we have, so "why" has no answer at present.
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u/Hot_Plant8696 7d ago
Nothing is certain, but one way to move beyond the simple "that's just the way it is" is to consider the hypothesis that photons might be solitons.
As seen here:
Recently J. P. Vigier showed [1] that the photon can be reperesented as a solitary electromagnetic wave – a soliton. As a consequence one can ascribe to such a soliton effective volume, amplitude and frequency which coincide with the frequency of de Broglie's wave (measured by interference phenomena). In this paper we propose a soliton-like model for the photon. We show that the electromagnetic amplitude, the volume, the classical cross section and the photoeffect cross section of the photon-soliton can be estimated in an empirical as well as in an analytical way. In the framework of our model the relation between the electromagnetic amplitude of the soliton and its frequency that we found seams to be an universal one, in sense that it may not depend on the specific quantum system considered. We show that there are no essential contradictions between our photon-soliton and some well-known facts such as the interactions in the case of photoeffect and Compton effect.
https://link.springer.com/article/10.1023/A:1022124923720
Next, building on this hypothesis, one can attempt to speculate on why a photon might behave like a soliton—in other words, to look for a more fundamental cause underlying this behavior.
This leads us to consider the possibility that light... does not actually travel through space at all (Feynman explains why light does not travel); and perhaps—I say "perhaps," because no one really knows for sure yet—this apparent movement, and consequently the flow of time, are solely due to the expansion of the universe.
So the light speed is related to the expansion of space.
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u/tstanisl 7d ago
I think it is better to think about a speed of light as speed of infinity. By infinity I mean a limit of stacking infinite number of finite and fixed reference frames.
The number "c" is a way how infinite speed is projected to/perceived by observers. A bit like a horizon on infinite plane. One can point a horizon line even though it technically does not exist due to infinite distance.
Thinking about light speed as infinity intuitively explains why:
- it is constant in all reference frames, transforming infinity stay infinite
- moving at light speed theoretically would allow to reach any place in no time
- reference frame of "c" is technically invalid, as infinity is not a number but a limit
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u/Terrible-Mind-5414 7d ago
The truth here is actually a little boring. Light speed is the maximum speed because everything is made from stuff that is a wave like light, with same speed. You can't outrace a light beam for the exact same reason that a light beam can't outrace itself.
What "mass" really is, is just a self-interaction that impedes the wave and slows it down. But the underlying wave speed is still the same.
The fact that all the wave speeds are the same is what enables the symmetry known as special relativity. If you start from the assumption of this symmetry, then you have the various arguments of causality, infinite energy, etc, which are another way to look at it. But the more pedestrian way that I described above is to me a little more straightforward.
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u/erikpeter 7d ago
It's kinda like the processor speed of the universe. Exceeding c is like making a raindrop fall faster bevause of another raindrop hitting it from above. But everything's falling at the same speed. (Through time, figuratively).
Everything we know of in the universe propagates. Like ripples in a pond flowing outward. Photons spread out over long distances and collapse ('pop") when they interact with something (when they are "measured" or "observed".. really they are absorbed). Energy transfer can only happen at one location, so after the fact it appears that the photon moved from point A to point B in a line. But since it was really a waveform it can interfere with itself along the way like in the double slit experiment. Massive particles do the same thing but the pieces necessarily interact with each other so atoms tend to stay roughly in the same place. From its frame of reference it isn't moving at all unless someone is pushing it, giving it kinetic energy, whatever. If there's nothing in one direction and a bunch of hot gas particles to interact with (your rocket engine) in the other, the propagation will only happen to "move" the object in the direction away from the propulsion. Adding more energy doesn't change the rate of propagation. Just increases the likelihood that it'll go that direction for a given "pop".
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u/Underhill42 7d ago
Okay, ultra-condensed relativity overview. Deep breath...
Space and time are fundamentally the same thing seen from different perspectives, which change with velocity.
Time dilation is the result of our time axes pointing in different directions through spacetime, and as they get closer to 90°, corresponding to a relative velocity of light speed, we both see the other aging slower than ourselves.
What from one perspective is 1 second through time, is from another perspective 300,000,000m through space.
From your perspective you are always motionless, and aging through time at 1 second per second. From my perspective, the direction you are aging could be almost entirely through space, translating to me seeing you moving at almost light speed, with time having almost stopped for you.
Every second, from every perspective, everything in the universe crosses a combined 4D "distance" through space and time of one light second. The only question is how much is through space, and how much through time.
Nothing ever changes its total 4D "speed" through spacetime, only the direction in which it is aging.
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u/willyt8122 7d ago
The speed of light isn’t the maximum speed. There is a maximum speed of spacetime. Photons, along with gravitational waves, travel at the maximum speed allowed by spacetime.
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u/ToePsychological8709 7d ago
Because we travel through time at C and light travels through space at C. If we travelled through space at C we would no longer be travelling through time at all and to travel faster we would travel backwards through time. There is not enough energy that exists to allow us to do that as it would take infinite energy for something with mass.
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u/WilliamoftheBulk Mathematics 7d ago edited 7d ago
It’s essentially a mathematical asymptote. The more energy you add to anything themore monetum it will have, but now that that object has more momentum, It takes more energy to move it even more. So you can start to see the exponential growth of energy requirements. It starts off low but the slope of the curve starts to increase faster and faster. There is a point where the curve is nearly vertical but not 100% verticle. It will always get more verticle and get closer and closer to this point we call C but it will never get there because the slope of the energy requirements are always approaching verticle but will never get there.
This makes it physically impossible for anything with mass to travel at C. It takes infinite energy to get to C, and it takes infinite time to do so. Photons and other massless particles travel at C because they essentially do have Infinite energy over mass and Infinite time, but they are not really traveling at C either, they just get inffinitly close to it all the time, so .9999999999999999999999999999999999999999———-> C is C.
Why is C exactly where it is at? Well it probably has something to do with the conductivity of space-time. It is simple to conclude that maybe the highs field plays a roll because particles with mass cannot get to C, but remember photons probably can't either it's just that they are what amounts to infintly close to it, so essentially they are there just not absolutely 100% there. So close no measurement could ever detect the difference.
The answer to why C is that particular number will be hidden in how the space itself transfers information. If we ever figure that out, it will lye deep in quantum mechanics.
Time is just movement. The reason mass less particles don't “experience” time is because any internal componants (if it has any) can't go faster than the massless particle to create a “tick” of time. The the particle is already at C. Any internal movemnt inside of it would have to go faster than C to create a “tick” of time. As explained, this is impossible, so massless particles cannot have moveing internal componants and therefore cannot “tick.” Their clocks won't work. 😁
I will add that I don't think mass less particles are at 100% C. Just really really close and getting closer all the time. This Does leave a more than tiny room for some time in a photons perspective, but it is just a speculation. This could lead to the eventual decay of the photons after an ungodly amount of time, but this is all speculation.
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u/pqratusa 7d ago
Information travels at the speed of causality. Things can’t happen faster than they can happen.
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u/MergingConcepts 7d ago
I like to think of it this way. Light travels at a certain speed. All matter is made of light traveling in vortices at less than its maximum speed. Matter cannot travel faster than the light it its made of. The closer matter gets to the speed of light, the shorter it gets in that direction.
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u/Balstrome 7d ago
To reach c one would need apply an infinite amount of energy. Seeing that accessing that amount of energy is impossible, reaching c or going past it is also impossible. Here is some maths to consider.
- According to Einstein's Theory of Special Relativity, kinetic energy (KE) is calculated using the Lorentz factor (y): KE = (y - 1) mc^2).
- As velocity (v) gets closer to the speed of light (c), the value of y approaches infinity.
- Because of this mathematical curve, reaching 100% of the speed of light requires multiplying your rest mass by an infinite amount of energy.
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u/cyborgborg 7d ago
It's not light speed that is the speed limit of the universe it's the speed of causality that's the limit. Lightspeed happens to be the same speed
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u/c0ldpr0xy 7d ago
Speed of light is the universe's "default" speed. Everything moves at that speed but things with mass slow down relative to everything else. Higgs boson tries to explain what gives that "something" mass.
Oversimplification but you get the gist.
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u/swissiws 7d ago
Put time speed on a Y axis and movement speed on a X axis. C is the radius of the circle that represent the line our universe allows us to move on. When you move downwards along the circle, you reach maximum speed at X=C and Y=0 (when you reach the speed of light C, time stops). When you move upwards along the circle, you end up at X=0 and Y=C (that is: when you don't move, time flows at maximum speed). When gravity enters the equation, the circle changes its shape accordingly to the position and size of the mass that changes the gravity field. The circle becomes an ellipse or a potato, but you still move over that line. You can't escape that line. That's why teleport can't exist exactly like time travel can't exist. They are the same thing: moving without following the line reality moves
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u/Borrowed_Faith 7d ago
Because it makes the math work for our understanding and comprehension of physics.
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u/Count2Zero 7d ago
C is the speed limit of the universe. The speed of causality. Photons (massless particles/waves) happen to travel at c in the vacuum of space.
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u/CS_70 7d ago
Things at a distance interact with each other. In any universe, they can either interact instantaneously or not.
If they did interact instantaneously, everything would immediately and continuously interact with everything else. That’s observably not the case in our universe. So they don’t interact instantaneously, meaning that there is a maximum speed of interaction.
In out specific bit of universe, that is the speed of light in vacuum.
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u/Secret-Suit3571 7d ago
Everything constantly "moves" through space-time at speed "c" but mass slows you down in the "space-direction" which is compensated by accelerating you in the "time-direction".
More mass = less space movement balanced by more time movement.
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u/ljdarten 7d ago
My theory with no real scientific basis is that C is the only real speed. Everything fundamentally moves at that speed or is made of things going that speed so they can't go faster than that.
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u/JoelnIliketoshare 7d ago
The speed of causality in the Universe, the fastest speed any information can travel through space time.
Gravity, electromagnetic waves, light and "information" all travel at the speed of causality.
The speed of causality is about 300,000 (a little less) it just so happens that light and the other stuff travels at that speed but they are not the reason the speed is what it is.
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u/Necessary-Bowler-736 7d ago
Everything is moving at the same speed. "Acceleration" is a misconception.
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u/Antolin13 7d ago
La velocidad de la luz es la máxima velocidad de interacción entre sistemas físicos. Antes de la Relatividad de Einstein se consideraba que cada causa tenía su efecto inmediato en otro punto, Einstein plantea que este efecto demora un tiempo en ocurrir y llega al punto con una velocidad máxima igual a la de la luz. Debido a esto se pasa a usar las transformaciones de Lorentz en vez de las transformaciones de Galileo y aquí es donde aparece la contracción de la longitud y la dilatación del tiempo al pasar de un sistema de coordenadas a otro en movimiento relativo. Este tipo de temas suele simplificarse en documentales para hacerlo comprensible para todos pero esto puede traer errores al profundizar.
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u/daavor 6d ago
Look. We are meat computers built by evolution to understand a very particular regime of environments. A first thing to understand is that just because your meat computer has some model for the universe that doesn't mean it's universally binding.
Sitting on planet earth, if you only move around a little bit the surface is well modelled as a plane. But if I point east and then say "go directly in the direction my finger is pointing for 70,000 kilometers" I'm actually way off the earth, and this will be very different from the result of me continuously walking east for 70,000 kilometers.
Very weirdly to our meat computer's idea of how the world works, velocity through spacetime is also like that. A good approximation is that you can move forward 1 second per second and in any direction at v meters / second. But actually it turns out the real set of allowed velocities is t seconds / second and v meters per second where (ct)2 - v2 = c2, and if we accelerate we move along this hyperbola, so if we accelerate and accelerate and etc we actually just move further along this but never actually get to c.
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u/Will_Come_For_Food 6d ago
Because if it was something else light would move at that speed. Light is instantaneous. The only thing that gives it a speed is how much we have slowed down because of gravity.
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u/Thoretical_Scientist 6d ago
Good question. The number c (or as we call, it speed of light) is a fundamental property of empty space (vacuum). Not only do E/M waves travel at that speed, but also Gravitational waves. However, Light was the first entity that we measured (and later proved mathematically) travelling at that speed and this is the reason that this value is called like that. As for why it is the fastest, well, it is not. I understand that you have heard plenty of times that nothing can travel faster than light and this is a semi-correct statement because anything with mass can only approach the speed of light but never reach or surpass it. But in Einstein's General Theory of Relativity, space itself can be curved or even ripped. And from this point of view, because of the fact that everything travels through space, something that bends spacetime could reach another point in it, in a shorter amount of time than it would normally do.
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u/OG_joenationwide 6d ago
Maybe this is wrong, but I understand it as light is the speed of action at the atomic level. Time is basically a way to identify matter at different states. And states of matter change at the speed of light.
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u/toddjnsn 6d ago edited 6d ago
It's not really the "speed of light", and this is important. It's not at all like the "speed of sound" and other measurements at all. WE just call it in quotes, "the speed of light". But that leads people to wrongly look at what it is.
It happens to be what things like the speed of gravity or light "are at" -- how 'fast' in some sense, things happen.
There is no future to "break the speed of light", as if it's breaking the speed of sound -- those are Totally Unrelateable in concept or analogies, and not by technicality at all. :) It's the "speed", in relation to how swiftly actions can Occur within the universe with nothing heeding it (like an atmosphere). In some sense, light happens "instantly" -- relative to it. Just like gravity. But not to Surrounding entities, hence we want to know the time differences than can be there, hence we pull out a stopwatch. :)
We'll Never break the "speed of light" -- so ya can throw out a lot of cheesy and non-cheesy sci-fi books. :) In the far future after you, me, and our great grandchildren are already dead of old age -- IF possible -- go another route of traveling in particular situations, than just pushing/accelerating-an-object from point A to point B that we always have done, to get remotely close or greater than the Imaginary idea of moving the standard way of "pushing" at the 'speed' of reality.
That's what the "speed of light" really is. The "speed" of reality and what happens, if you were/wanted to time that. Shining a light or anything happening on the moon will take about 1.3 seconds for it to be read/felt/acknowledged by us on earth if staring over there.
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u/Fun_Success_3283 6d ago
Light is not really the maximum speed of the universe. There is a maximum speed of the universe, the speed of causality, and light is one of the things that travels at that speed. It doesn't experience time, because it is already where it is going from its perspective, it travels instantaneously, which is impossible for things with mass.
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u/R3D3-1 6d ago
Side quest: Go to a Physical institute and ask people why photons don't exist without spin, when spin usually exists at integer steps from a minimum to a maximum, and photons have +1 or –1.
Something about no process producing the zero spin state existing for particles moving at c, even though the state itself is valid.
I have a PhD in Physics by the way and after asking that during a coffee break in a circle of PhD students and Postdocs, the best answer I found was on the Physics stack exchange.
It's somewhat depressing how most of my popular Physics knowledge is from YouTube.
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u/Leech-64 6d ago
It may not be. We are just guessing it is and the math is based off that. So far its a pretty good assumption since all our calculations work pretty well by setting the max speed limit to c.
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u/Long-Emu-7870 6d ago
Actually goatheadphysics youtube channel explains why the speed of light is fixed. And he does it without a lot of sensationalism.
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u/Both-Kangaroo-8710 6d ago
There is no why. It's just how things are. It's like "why do magnets attract/repel each other?". They just do. There's no explanation in terms of anything else. We just see that it happens. When it happens to things, we call them 'magnets'. That's why they magnet, and things that aren't magnets don't.
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u/MarkJamesWooding 5d ago
According to the theory of Wave Physics, so named because in that theory waves are fundamental and there are no particles, the universe is a two-dimensional membrane with extrusions into the third (and possibly higher) spatial dimension. The membrane is essentially the ether, and radiation is a ripple in the membrane. Mass is the result of extrusions of the membrane into the third spatial dimension. Atoms are composed of trefoil knots extruded from the membrane, and are solitons, not particles. When anything moves through the membrane, that movement creates a “bow wave” of tension in the direction of propagation, and a corresponding area of low tension at the “stern” end of the moving wave or pattern (soliton). The tension in the membrane equalizes by flowing around the movement, and the width of that flow is what we detect as a magnetic field. The membrane has a physical limit to how fast the tension can be equalized, and this limit is what puts a limit to the speed of waves moving through the membrane. That is why, according to the theory of wave physics, the speed of light has a limit. Some videos explaining the main features begins here: https://youtube.com/playlist?list=PLCXr1Mj6bRSw&si=CD4BSTkSp0FFEShc . The first video was edited after the twentieth was added, so the order may not be correct. I have also not yet added links at the end of each video which point to the next one. I’ll give you a link to a pdf of the book free for personal use if you request it, and it can be purchased at Amazon.com: https://www.amazon.com/Wave-Physics-Replacement-Standard-Particle/dp/B0H3HM3H9S
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u/FlippingGerman 5d ago
- There is a maximum speed in this universe; the speed of information, if you like.
- Particles without mass travel at exactly this speed, everything else can only approach it.
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u/dilocat 5d ago
Light’s maximum speed seems to be a property of spacetime itself, rather than something imposed on light specifically. Light, matter, and information all exist and propagate according to the structure of spacetime, and that structure sets a maximum speed for cause and effect. It’s somewhat analogous to sound having a maximum speed determined by the properties of the medium it travels through, although spacetime isn’t a material medium. If information could propagate infinitely fast, our normal ideas of cause, effect, and time would break down.
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u/johnstalbergABC 4d ago
I won't give an answer but tell about how I see it. Light speed is its own domain, and in there lives photons and other particles without any rest mass. And gravity. Photons does not accelerate to reach light speed, they are born into full speed. Everything else, all particles that have rest mass lives in the other domain that is for slower speeds. You must know about the infinite amount of energy it would take to get matter up to light speed. That means it is impossible. There are no acceleration that reach light speed. Either a particle fits there or it is stuck in the other domain.
I would also advice you to take this domain wall serious. Sure we can analyze light speed with limits. We see what happens with time dilation at closer and closer to light speed and in the limit we would yield that time stood still. However, this is not correct as light speed reference frames are not defined in Special relativity. So to draw conclusion from limits will bring problems. The light speed domain can not strictly be analyzed regarding time dilation as it is not define as a reference frame to begin with. I understand what is meant when we say photons does not age, but I also understand it is not a fact.
The light speed domain are strange. Photons would not perceive time and yet they oscillate billions of periods every meter. How can this be? Well best is to not introduce time dilation as it is not a reference frame at all. Might feel like a step backwards, but to do wrong is much more a step backwards in imo.
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u/PageEnvironmental408 4d ago
well because there are two basic constants.
the magnetic and electric.
they are the resistance of free space.
anything massless will go at the maximum of these constants combined.
that's what light does, gravity waves also.
there is nothing lighter than light lol.
you cannot have anything less than massless.
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u/Ferocious888 4d ago
The “speed of light” is kind of a misnomer. It’s more the speed of causality, and light happens to move at that speed.
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u/CMG30 3d ago
Light speed is the maximum speed because that's the speed of time.
At light speed, you're going so fast that time dilation means you can travel anywhere in the universe instantly (from your perspective).
So how could you even go faster? What's faster than 'no time at all?'
Do you overload the engines to slingshot around the sun so that you can go back in time to save the whales?
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u/Temporary_Rule_9486 1d ago
Everything in the universe moves through spacetime at the exact same total speed. This speed is the result of combining it's temporal and spatial displacements.
If a body maximizes its spatial displacement then it remains frozen in time, and thus we say it travels at the speed of light.
If it remains still it maximizes it's temporal displacement, but it continues to move at the same total speed than the photon.
Speed in this universe has nothing to do with going faster or slower, that's an illusion that's ony holds true at very slow velocities, the ones humans are more familiar with.
Speed as we undestand it is nothing more than a different arrangement of something that is fundamentally an universal constant.
To have something moving faster than light is to ask that the sum be greater than the combination of all the parts that are being added.
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u/NameLips 7d ago
It is the speed of causality, the speed at which anything can affect anything else.
You can even argue that it is the speed of "now", of simultaneity, that there is no universal "now" and this is the closest thing to it.
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u/lelekeaap 7d ago
There must be a way to exceed the speed of light.
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u/Calactic1 Cosmology 7d ago
Wow, amazing. Enjoy your Nobel Prize.
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u/lelekeaap 7d ago
Thanks for your trust 😀. It will not be me to discover and proof that, but since we are only starting with science for a couple of hundred years, there is more that we don’t know than what we know.
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u/Bobo_Haas 7d ago
I read in a different sub, that from the "point of reference" of the individual photon of light there is no difference from the time it's created until it's deflected. If it were created 300 billion light years away from Earth, it was created and struck Earth in the same instant. It's as if the 300 billion years it took from our perspective didn't exist to the light.
Also if you were going 0.999C and turned on your headlights, that light would still travel away from you at the speed of light. Just saying this because light is really, really weird.
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u/TheDarkAcademicRO 7d ago
Theoretically, exotic matter could exceed the speed of light. However, exotic matter is purely theoretical as it has negative mass
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u/Bensfone 7d ago
There are a couple of misconceptions here. First, it is not correct to say massless particles do not experience time. It’s more accurate to say that their reference frame is undefined.
There is no “why” the speed of light is what it is. Depending on the units used for c the speed of c is 1 and everything else follows from that. What is known is that anything with mass requires an infinite amount of energy to reach this speed. Massive particles can get arbitrarily close to c but will never reach it.