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[Trent Strong]

As far as I can tell from the thread, they just can't. It's a rule of the universe. I honestly don't think there's much point trying to find a reason for it because there isn't one.

I guess you're right that they can't explain why. But I think there is a reason, we just don't know what it is yet (and maybe we never will). In fact, it seems impossible that there is no reason. Everything is part of a causal chain.

What are you looking for here? Information cannot exceed C. Ergo, it's the speed limit for anything that can exert causal influence. If you're just doing some "Why why why" stuff, you can stop now because physics will never satisfy you. It can tell you how things are, never why they are.

Physics sucks if it can never answer any "why" questions. But I find it hard to believe that an answer to why this speed limit exists is unknowable and can never be discovered.

 

[The Technomancer]

I guess you're right that they can't explain why. But I think there is a reason, we just don't know what it is yet (and maybe we never will). In fact, it seems impossible that there is no reason. Everything is part of a causal chain.

Yeah one of the big questions in physics today and the foreseeable future is why the universe is the way it is. Why is the speed of light what it is? If you look at a table of known particles sometime you'll notice that there are incredibly arbitrary numbers for how many varieties there are in a family. Why are those numbers what they are?
This is one of the things that got people excited about string theory before it became apparent that we really have no way to verify anything about string theory.

 

[The Shadow]

OP is incorrect. Though the relative speed of objects can't exceed the speed of light, the region of space between two objects can can expand faster than the speed of light.

Edit:

Also, that only applies to light in a vacuum. For a visible effect of electrons exceeding the speed of light through a medium, read up on Cherenkov radiation:

http://en.wikipedia.org/wiki/Cherenkov_radiation

 

[ThoseDeafMutes]

Physics sucks if it can never answer any "why" questions. But I find it hard to believe that an answer to why this speed limit exists is unknowable and can never be discovered.

You get why answers until you get down to basic building blocks, the postulates that the universe obeys without explanation. Essential properties that cannot be divided or explained further. That is what physical laws are, in their most basic. The rules for how things behave. This has to happen at some point - even if you can explain some things that are mysterious today, you will never have satisfying answers to the most fundamental of things that replace the current mysteries.

 

[panama chief]

im no science major.....but whats stronger/faster:

the speed of light?

or

the gravitational effect of a black hole?

leading to my question: does light travel faster as it enters the vacuum of a black hole or does it just disperse? i know light cannot escape....it is cause it isnt "fast" enough?

 

[ThoseDeafMutes]

im no science major.....but whats stronger/faster:

the speed of light?

or

the gravitational effect of a black hole?

leading to my question: does light travel faster as it enters the vacuum of a black hole or does it just disperse? i know light cannot escape....it is cause it isnt "fast" enough?

Both gravity and photons are bound by the light-speed-limit. All objects have a concept of "escape velocity", that is the speed at which it must be going at in order to escape the gravity of something else (to have distance between it and the body exerting force on it to be increasing). The event horizon of a black hole is the point at which the escape velocity becomes higher than the speed of light, and thus, light cannot escape.

 

[Norml]

Quantum Entanglement is faster.

 

[Trent Strong]

You get why answers until you get down to basic building blocks, the postulates that the universe obeys without explanation. Essential properties that cannot be divided or explained further. That is what physical laws are, in their most basic. The rules for how things behave. This has to happen at some point - even if you can explain some things that are mysterious today, you will never have satisfying answers to the most fundamental of things that replace the current mysteries.

Well, yeah. I don't expect physicists to be able to know and explain everything.

Yeah one of the big questions in physics today and the foreseeable future is why the universe is the way it is. Why is the speed of light what it is? If you look at a table of known particles sometime you'll notice that there are incredibly arbitrary numbers for how many varieties there are in a family. Why are those numbers what they are?
This is one of the things that got people excited about string theory before it became apparent that we really have no way to verify anything about string theory.

Looks like we won't know any of this in our lifetimes.

 

[panama chief]

Both gravity and photons are bound by the light-speed-limit. All objects have a concept of "escape velocity", that is the speed at which it must be going at in order to escape the gravity of something else (to have distance between it and the body exerting force on it to be increasing). The event horizon of a black hole is the point at which the escape velocity becomes higher than the speed of light, and thus, light cannot escape.

but does it travel faster as it goes in, given this super high amount of gravity?
or is that something unquantifiable?

 

[The Shadow]

im no science major.....but whats stronger/faster:

the speed of light?

or

the gravitational effect of a black hole?

leading to my question: does light travel faster as it enters the vacuum of a black hole or does it just disperse? i know light cannot escape....it is cause it isnt "fast" enough?

Think of it as escape velocity. We need huge rockets to launch payloads into earth orbit. For a black hole, the escape velocity is much greater, so great that it exceeds the speed of light.

To answer your second question, no. Light in a vacuum is always going at the same speed. It doesn't accelerate but it does decelerate when it goes through a medium like water or a gas. The reason why black holes are black is because of the universal speed limit that is the speed of light. If things could go faster, even light, black holes wouldn't be black because it would be possible to approach that escape velocity.

 

[ThoseDeafMutes]

but does it travel faster as it goes in, given this super high amount of gravity?
or is that something unquantifiable?

No. Regardless of your own speed, light always seems to be moving away from you at the speed of light (whether you're going at 0.999C or 0.00001C relative to it). This is actually one of the fundamental postulates of Relativity. Light "escaping" black hole is not slowed down (unless it is diffracting, I guess?), but light trapped by it never escapes at all (and is not seen). Conversely, it cannot speed up any faster, light moving towards a black hole does not go faster than light while getting "sucked in".

 

[panama chief]

Science!!

Extra Science!!

thank you both for the quick replies. sent me to bed a bit more knowledgeable....something we need more of on this planet.

 

[Platy]

I honestly don't care much about FTL. Light-speed would be good enough.

Good Enogh ?????

Also ... if the idea of a ship going by insanely close to the speed of light ..... if you take an insanely fast rocket and launch inside the ship ... can it go faster than the speed of light ?

 

[DonasaurusRex]

well well, the bastard step child that is linear algebra has the last laugh . nice article.

 

[ThoseDeafMutes]

Also ... if the idea of a ship going by insanely close to the speed of light ..... if you take an insanely fast rocket and launch inside the ship ... can it go faster than the speed of light ?

No, and if you have a train going the speed of light and then you went up to the roof and ran forwards, you wouldn't be going FTL either.

 

[akira28]

Who would want to go lightspeed or FTL in relativistic 3d space anyway? Screw that shit, aside from being tough, its fuckin dangerous. I need some space-time manipulating field or no deal. Or dimensional something or other that equates to fast travel. Why waste time trying to attain speed of light? It's too hard and the payoff isn't there. Figure out a way around it that ain't so hard then.

 

[Raistlin]

To the above poster: there is no such thing as a perfectly rigid body. Compressive waves would travel down the stick, at no faster than the speed of light.

Actually I'm aware of the physics, I just found the pic amusing ... particularly given my avatar

 

[The Shadow]

Good Enogh ?????

Also ... if the idea of a ship going by insanely close to the speed of light ..... if you take an insanely fast rocket and launch inside the ship ... can it go faster than the speed of light ?

No, because of time slowing down the closer you approach c. From the interior of the ship, it would look like the rocket went insanely fast and exceeded the speed of light because the ship surrounding it is going near the speed of light. It would look the same as if the ship were stationary. However, observers on the exterior looking in the windows of the near FTL ship would see extremely slow people launching an extremely slow rocket that no where near approaches c, from their perspective.

 

[BudokaiMR2]

You guys are just silly.

Everyone knows now that we just need to figure out what exactly the fuck dark matter/dark energy is so we can then understand that remaining 80% of the world.

Then we just gotta figure out how to fold it and BAM! SPACE TRAVEL GREAT SUCCESS!

 

[Raistlin]

Quantum Entanglement is faster.

Good point to bring up in this discussion. While I am fairly familiar with special and general relativity, I'm admittedly quite ignorant of quantum mechanics beyond some of the more popular, high-level theories.

Can someone extrapolate on this phenomenon?

 

[ThoseDeafMutes]

Good point to bring up in this discussion. While I am fairly familiar with special and general relativity, I'm admittedly quite ignorant of quantum mechanics beyond some of the more popular, high-level theories.

Can someone extrapolate on this phenomenon?

Quantum entanglement cannot be used to transmit information faster than light, even though the phenomenon itself is instantaneous. Additionally, other FTL phenomena such as phase velocities greater than C in X-rays cannot be used to transmit any information. Virtual particles also travel faster than light in many cases. But they disappear before they can do anything.

Once again, "information" here is defined as "the ability to exert a causal influence". Entangled bits that have been manipulated cannot be told apart from what it would have otherwise been, because of the random nature of QM. So long as information cannot exceed C, relativity is not violated. Unfortunately, all "useful" FTL (instant comms, warp drive) must involve this by necessity.

 

[Slavik81]

im no science major.....but whats stronger/faster:

the speed of light?

or

the gravitational effect of a black hole?

leading to my question: does light travel faster as it enters the vacuum of a black hole or does it just disperse? i know light cannot escape....it is cause it isnt "fast" enough?

Light doesn't travel faster as it falls into a black hole, but it does gain energy. Low frequency light becomes high frequency light as it falls. It's a 'blueshift'.

 

[thirty]

The whole future and past thing make no sense. We only have a concept of time because we have a limited time on earth. You're never moving forward in time only closer to death lol. Trees are alive but have no concept of time because they just sit there mindless. Wtf. The whole concept of time is stupid. All it is is a measurement.

 

[Slavik81]

The whole future and past thing make no sense. We only have a concept of time because we have a limited time on earth. You're never moving forward in time only closer to death lol. Trees are alive but have no concept of time because they just sit there mindless. Wtf. The whole concept of time is stupid. All it is is a measurement.

thirty
DEFINITELY NOT
a Physics Major
(Today, 02:28 AM)

Spoiler

I'm sorry, I couldn't resist.

 

[ThoseDeafMutes]

The whole future and past thing make no sense. We only have a concept of time because we have a limited time on earth. You're never moving forward in time only closer to death lol. Trees are alive but have no concept of time because they just sit there mindless. Wtf. The whole concept of time is stupid. All it is is a measurement.

thirty
DEFINITELY NOT
a Physics Major
(Today, 04:28 PM)
Reply | Quote

EDIT:

thirty
DEFINITELY NOT
a Physics Major
(Today, 02:28 AM)

Spoiler

I'm sorry, I couldn't resist.

OH GOD DAMMIT.

 

[IrishNinja]

wall o' text, sure, but it is indeed easy to understand. thanks OP.

 

[Raistlin]

Quantum entanglement cannot be used to transmit information faster than light, even though the phenomenon itself is instantaneous.

I guess this is where I, as a plebe, am a bit confused.

If the information transfer is 'instantaneous', as you contend, ...

 

[ThoseDeafMutes]

I guess this is where I, as a plebe, am a bit confused.

If the information transfer is 'instantaneous', as you contend, ...

QE doesn't transmit information, that's the point. In order to realize that particle A has done something to particle B, you must have knowledge of both A and B, which can only be transmitted via classical channels. So while A did instantly have an effect on B, you can't know it did until you have already transmitted info at light speed between A and B. The reason you can't know is because quantum systems are indeterminate.

 

[AlimNassor]

Exactly.

Fifteen hundred years ago everybody knew the Earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and fifteen minutes ago, you knew that humans couldn't move faster than light. Imagine what you'll know tomorrow.

No we didn't. Even during early Roman times people knew the Earth was round. People don't give early man enough credit.

 

[thirty]

Huh? He kills the whole concept of time in his whole example of the train. Even if you can't feel it moving and you get somewhere you didn't move "toward the future" you just moved a distance and measured it with time. Again if we had infinite life, you wouldn't even measure that distance. Or if you did it would only be to know how long it takes to get somewhere.

 

[Albino_Samurai]

gravity.

 

[toohectic]

I always thought this youtube series of 4 videos did a good job of explaining special relativity. Here's part 2 of 4, which covers the major points.

http://www.youtube.com/watch?v=WgsKlSnUO0k

 

[ShinNL]

I'm gonna join the group that says the OP's quoted explanation sucks. Read it all (+OP comments, before and after), never was the light link explained (why it is max speed). I got far better logic from the simple 1 line explanations by other posters after this story. I don't even get the part about "if you move faster, your time goes slower"...!??

 

[JonnyBrad]

I like:



Simple and straight to the point.

Yep that's the best way imo

 

[Regulus Tera]

This is a fucking amazing explanation. Much more intuitive than the traditional one. I urge you all to plow through it--you will then be able to tell your friends you understand general relativity.

Edit: Damn it, you lazy bums. Okay. Basically, time is another direction, and we're always moving at the same speed through time when we're perfectly still... but when we start moving in space, we're still moving at the same speed--just in a different "direction." So traveling faster than light makes no sense.

The thing I don't get is why light travels at that speed.

 

[ThoseDeafMutes]

I don't even get the part about "if you move faster, your time goes slower"...!??

There are two postulates in special relativity (a postulate is something that is postulated as being true, like foundational principles. They themselves aren't justified by the theory itself, although they are always based on something empirical, an experiment or something).

The first is the principle of relativity, which says that all frames of reference (in layman's terms, perspectives) have the same laws of physics, which never change. Thus, all frames are equally valid to measure from.

The second is the principle of the invariant speed of light - this says that the speed of light, C, is the same no-matter how fast you are going. If you are going at 99.999% of the speed of light yourself, light still moves away from you just as fast as it did when you were "resting" on Earth.

Now, the second one is confusing, but backed up by experimental evidence. People worked out that regardless of how fast they got a measuring object to go, it always measured the speed of light as the same, and likewise, light emitted from something moving was going at the same speed for people measuring it as when the light emitters were stationary.

Ok, so if light is always running away from you at the same speed, then how can this make sense? Here we run into two ways of "balancing the books", length contraction and time-dilation. Objects that are going at a high speed get shorter, and time passes slower. The combination of these two effects explains how this can be possible - your rulers (metaphorically, obviously physicists don't use rulers for tests of special relativity) get shorter, so rate at which the light is escaping you seems greater. Likewise, if your clock is ticking slower, then you won't measure the "one second" (to determine the speed of light in meters per second) like other people will. These two always combine to make it so that you always get the same speed when you measure the speed of light, regardless of how fast or slow you are going!

If these two effects didn't exist, then the invariant speed of light would be wrong. It couldn't happen. But we measure it to happen in labs, so something is going on. Decades later, we got lab confirmation that time dilation does actually exist, in several ways. The simplest is by using radioactive decay as a clock (since radioactive decay never changes), and putting radioisotopes in a particle accelerator. By measuring how much it has decayed in the accelerator vs how much the one at rest has decayed, they can determine how much time slowed down for the faster object.

 

[Slavik81]

The thing I don't get is why light travels at that speed.

That's a mystery, like the origin of a lot of other physical constants.

 

[ShinNL]

There are two postulates in special relativity (a postulate is something that is postulated as being true, like foundational principles. They themselves aren't justified by the theory itself, although they are always based on something empirical, an experiment or something).

The first is the principle of relativity, which says that all frames of reference (in layman's terms, perspectives) have the same laws of physics, which never change. Thus, all frames are equally valid to measure from.

The second is the principle of the invariant speed of light - this says that the speed of light, C, is the same no-matter how fast you are going. If you are going at 99.999% of the speed of light yourself, light still moves away from you just as fast as it did when you were "resting" on Earth.

Now, the second one is confusing, but backed up by experimental evidence. People worked out that regardless of how fast they got a measuring object to go, it always measured the speed of light as the same, and likewise, light emitted from something moving was going at the same speed for people measuring it as when the light emitters were stationary.

Ok, so if light is always running away from you at the same speed, then how can this make sense? Here we run into two ways of "balancing the books", length contraction and time-dilation. Objects that are going at a high speed get shorter, and time passes slower. The combination of these two effects explains how this can be possible - your rulers (metaphorically, obviously physicists don't use rulers for tests of special relativity) get shorter, so rate at which the light is escaping you seems greater. Likewise, if your clock is ticking slower, then you won't measure the "one second" (to determine the speed of light in meters per second) like other people will. These two always combine to make it so that you always get the same speed when you measure the speed of light, regardless of how fast or slow you are going!

This still doesn't make sense to me because you're just describing the observational effect, but if an imaginary clock is flying near the speed of light, it should still have the same time displayed as a stationary one (even if we can't observe it), no?

 

[Regulus Tera]

That's a mystery, like the origin of a lot of other physical constants.

The design of God.™

 

[Norml]

QE doesn't transmit information, that's the point. In order to realize that particle A has done something to particle B, you must have knowledge of both A and B, which can only be transmitted via classical channels. So while A did instantly have an effect on B, you can't know it did until you have already transmitted info at light speed between A and B. The reason you can't know is because quantum systems are indeterminate.

Crazy stuff:/ But I have faith guys like you will figure a way to do it.

 

[Slavik81]

This still doesn't make sense to me because you're just describing the observational effect, but if an imaginary clock is flying near the speed of light, it should still have the same time displayed as a stationary one (even if we can't observe it), no?

Nope. You'd see the clock hands spinning around very, very slowly as it passed you by. If there were a person in the ship with the clock, he'd see nothing wrong with the clock, but you'd see him moving incredibly slowly too.

 

[ShinNL]

Nope. You'd see the clock hands spinning around very, very slowly as it passed you by. If there were a person in the ship with the clock, he'd see nothing wrong with the clock, but you'd see him moving incredibly slowly too.

But observation =/= reality...? I'm not talking about when the light rays hit me, the clock's time should still be functioning good.

 

[ThoseDeafMutes]

This still doesn't make sense to me because you're just describing the observational effect, but if an imaginary clock is flying near the speed of light, it should still have the same time displayed as a stationary one (even if we can't observe it), no?

Hang on, I edited some new stuff in the old post:


If these two effects didn't exist, then the invariant speed of light would be wrong. It couldn't happen. But we measure it to happen in labs, so something is going on. Decades later, we got lab confirmation that time dilation does actually exist, in several ways. The simplest is by using radioactive decay as a clock (since radioactive decay never changes), and putting radioisotopes in a particle accelerator. By measuring how much it has decayed in the accelerator vs how much the one at rest has decayed, they can determine how much time slowed down for the faster object.

So to answer your question: NO, clocks going at lightspeed tick far slower than ones that are at rest. In addition to the particle accelerator one mentioned above, we have measured time dilation by comparing clocks on satellites in orbit around the earth (which go somewhere in the region of Mach 25+ at all times to maintain orbit) to ones at mission control. The clocks on the GPS satellites get resynchronized every day with Earth to prevent them from drifting too far apart.

 

[Regulus Tera]

Massless particles travel the speed of light. Photons, which make up light, are one of those particles, but there are others. These massless particles are the fastest "things" in the universe because they move through spacetime with a velocity that is as fast as the universe will allow; they go the speed limit of the universe. There is nothing that can travel faster in a universe in which relativity applies. The universe itself has set the limits.

This answers my previous question. Basically, light travels as fast as possible because it has no mass, so energy yadda yadda.

Math is God.

 

[Slavik81]

But observation =/= reality...? I'm not talking about when the light rays hit me, the clock's time should still be functioning good.

Let's back up a second.

Alice has a clock and is flying on a spaceship travelling near the speed of light, and Bob has his own clock and is just watching while standing still.

When Alice first left on her trip, Bob's and Alice's clocks both agreed on the time. When Bob looked in the windows of Alice's spaceship, he saw Alice and her clock moving really slowly. Alice's clock falls more and more behind Bob's clock.

Alice comes to the end of her trip and slowly comes to a stop. As she does so, Bob sees her slowly begin to move more normally and the clock slowly starting to move at the same rate as his.

Eventually, Alice and Bob are both at a complete stop. Now their clocks are running at the same speed and neither is falling behind. At that point, Alice's clock says less time has passed than Bob's. She thinks she made the trip faster than Bob thinks she made the trip.

This is true even if the trip was a loop. At the end, Bob and Alice would be standing right next to each other with different opinions of how much time had passed since they last met.

 

[Scrow]

Relevant

Study finds single photons cannot exceed the speed of light

The whole future and past thing make no sense. We only have a concept of time because we have a limited time on earth. You're never moving forward in time only closer to death lol. Trees are alive but have no concept of time because they just sit there mindless. Wtf. The whole concept of time is stupid. All it is is a measurement.

time is another dimension that you travel through. trees don't need to "know" anything, just like all the cells, atoms, sub-atomic particles etc. that make up you don't need to have a concept of what time is. they just travel through it. does a box sitting on a truck need to have a concept of space to be capable of moving?

I don't even get the part about "if you move faster, your time goes slower"...!??

move forward in the direction you're facing. now turn a little and continue walking. you're still walking generally in the initial direction you started with, but not as quickly. now imagine that instead of travelling through space you're travelling through time. change your movement through space and you change your movement through time.

The thing I don't get is why light travels at that speed.

it's restricted by time.

 

[The Shadow]

This still doesn't make sense to me because you're just describing the observational effect, but if an imaginary clock is flying near the speed of light, it should still have the same time displayed as a stationary one (even if we can't observe it), no?

The clock flying near the speed of light is quite literally traveling slower in time. Atomic clocks on jets measure time slower than stationary atomic clocks. This has been tested and proven to be true time and time again.

As a matter of fact, the GPS satellites have to take in the time dilation effect because of their distance from earth and the speed at which they travel.

 

[ShinNL]

So you guys are saying that time travel is a real thing? I thought that was never proven :O
(Alice is meeting an 'older' Bob)

 

[Scrow]

So you guys are saying that time travel is a real thing? I thought that was never proven :O

everything in the universe is travelling through time right now.

yes, time travel is real as evidenced by all existence.

 

[mike23]

So you guys are saying that time travel is a real thing? I thought that was never proven :O

You're traveling into the future right now.

Also, I read that a person on the space station will be ~4 seconds younger than they ought to be when they stay up there for a year. So they traveled 4 seconds into the future.

That's really the worst thing about traveling at near light speed. This website shows the time dilation effects at various speeds.

http://www.fourmilab.ch/cship/timedial.html

When you're going 0.999999999999999c, every day that passes on the ship 61286.634 years would pass by on earth. Kind of defeats the purpose of traveling fast.