Nothing can go faster than twice the speed of light.

[Aggrophobic]

If movement is relative, then if you have one thing moving the speed of light one way, and another thing moving the speed of light the exact opposite way, than the truth is relativity means that nothing can go faster than TWICE the speed of light, since the gap between those two would be created at twice the speed of light.

Thats... not how it works.

[Deleted]

your logic is flawed. If I am running in one direction and Usian Bolt is running in the other direction from me then that doesn't mean I am running as fast as me + Usian Bolt combined you genius.

If you have a radar device and you run in one direction while someone else comes from the opposite direction, the radar will pick their speed as your spped + theirs. Technically, while neither of you have that speed, the speed of the other compared to your speed is seen as that. Essentially the logic in the OP only works if we would measure speed from another moving object.

[Noradin]

It depends on how you define "move away from each other", I guess. The distance between the objects can increase at the rate faster than the speed of light, due to space expansion.

I define it as the velocity of one in the reference frame of the other and vice versa.

[May90]

I define it as the velocity of one in the reference frame of the other and vice versa.

The velocity can be local or non-local (for the lack of better terms). For local velocity, you are right. For non-local, i.e. observable, an object can move away from you at the speed faster than light; in this case, you will never see that object, because the red shift is infinite.

For example, near the very edge of the observable universe the space expansion makes the space move away from you at the speed 0.99c. If an object there moves at 0.99c relative to some object, away from you, then the distance between you and it will be increasing at the rate 1.98c (normal velocity summation is applicable in this case). You won't see it for that reason, but its gravitational effects will be observable, once the signal reaches you.

[Adam Jensen]

Hasn't it been proven that some particles can travel faster?

Neutrinos, for about a week.

Then it was discovered that the experiment had a measuring error of some type.

So . . . unless Tachyons exist (and there's no evidence that they do) . . . then no.

[May90]

Neutrinos, for about a week.

Then it was discovered that the experiment had a measuring error of some type.

So . . . unless Tachyons exist (and there's no evidence that they do) . . . then no.

There are some weird theoretical models that prescribe creating a temporary Higgs field to make an object's mass negative, and then, in some of those models, it could lead to the object being able to travel at FTL speed.

Of course, it is unlikely that it is possible in reality, and even if it is, it is not clear how it can coexist with the causality principle. And if the causality principle is wrong, then we are in for bizarre discoveries in the future...

[Adam Jensen]

There are some weird theoretical models that prescribe creating a temporary Higgs field to make an object's mass negative, and then, in some of those models, it could lead to the object being able to travel at FTL speed.

Of course, it is unlikely that it is possible in reality, and even if it is, it is not clear how it can coexist with the causality principle. And if the causality principle is wrong, then we are in for bizarre discoveries in the future...

This sounds like it would have some sort of . . . effect . . . on an object's mass. Like . . . a Mass Effect . . .

But seriously though, isn't that how Mass Effect's spaceship technology was suppose to work?

[Deleted]

If you have a radar device and you run in one direction while someone else comes from the opposite direction, the radar will pick their speed as your spped + theirs. Technically, while neither of you have that speed, the speed of the other compared to your speed is seen as that. Essentially the logic in the OP only works if we would measure speed from another moving object.

what happens if there are more than 2 objects moving in all kind of different directions?

[Deleted]

ITT: people applying Galilean relativity to light.

Also, some people who took a relativity course. Go go physics major.

That's really really sad

If movement is relative, then if you have one thing moving the speed of light one way, and another thing moving the speed of light the exact opposite way, than the truth is relativity means that nothing can go faster than TWICE the speed of light, since the gap between those two would be created at twice the speed of light.

Just grab a Special Relativity book and look for "speed transformation laws"...anyways keep in mind that speed of light in the vacuum must have the same value in every inertial frame, and that's an EXPERIMENTAL FACT. Michaelson and Morley experiment, pions decay (pions can decay in 2 photon emitted in opposite direction due the conservation of the momentum) and many others experiments are the proof.

[Deleted]

If movement is relative, then if you have one thing moving the speed of light one way, and another thing moving the speed of light the exact opposite way, than the truth is relativity means that nothing can go faster than TWICE the speed of light, since the gap between those two would be created at twice the speed of light.

The rule is that information can't travel more then the speed of light. The information being photons in this case. The space between the two photons isn't moving information. That's why shadows (which is the absence of photons) can move faster than the speed of light as well as the empty space between two objects.

[Khazaad]

Weeeeeeell, you have a point... But in reality, theoretically, things can go away from each other much faster than that, since the space is expanding.

The diameter of the Universe is around 92 billion LY (note that 14+14~28 billion LY is only the diameter of the observable Universe we can see, but it stretches far more than that at present). Hubble's Constant is 67 km/s per Mpc, or ~ 6.8e-11 LY/s per LY. So for 92 billion LY, we get roughly 6.3 speeds of light, and plus two speed of light from your reasoning, we get the maximum speed at 8.3 speeds of light.

Of course, this has very little physical meaning, since we can't physically observe something like that. We will be able to in 46 billion years though, so there is consolation!

EDIT: Actually, not in 46 billion years, but much later, since the space between the "border" and us is still expanding... Dang!

Actually you're not quite right. And IIRC you're a scientist, so I'm a bit surprised by that.

Particle horizon, or the observable universe in other words has a radius of 46 billion LY.

However, the cosmic event horizon, which is the furthest away point we can ever recive information sent NOW is estimated at a radius of about 16 billion LY. Further then that the space is expanding faster then light speed, and all information sent gets redshifted into nothingness.

What that means is we'll never be able to observe more of the universe then we can at the present, not even in 46 billion years. As the time goes by the size of the observable universe will be constantly shrinking.

[Forogil]

What that means is we'll never be able to observe more of the universe then we can at the present, not even in 46 billion years. As the time goes by the size of the observable universe will be constantly shrinking.

I thought the observable universe would be shrinking (as galaxies will drop out of it) - but the size of the observable universe would be expanding (as in the farthest galaxy being a larger distance from us).

[Twix]

Lies. 3 lights = 3 times as fast as the speed of 1 light

[Evil Midnight Bomber]

That picture kind of proves how OP Flash is, and how he still cant win in every scenario is just stupid

I always thought it proves how bad Comic book writers are at science.

[Kokolums]

I thought the reason light speed is a limit is that at speeds faster than c, time breaks down and you start getting some really bizarre solutions to equations. Like if you launch a space ship at a speed faster than c, a second ship appears in the same place as the first one but before the launch even occurs (which doesn't make sense).

[Deleted]

I thought the reason light speed is a limit is that at speeds faster than c, time breaks down and you start getting some really bizarre solutions to equations. Like if you launch a space ship at a speed faster than c, a second ship appears in the same place as the first one but before the launch even occurs (which doesn't make sense).

Using Maxwell's equations and a bit of calculus you can find the wave equations related to the electric/magnetic fields. From there, you can derive the velocity of these waves, which is equal to c. One then has to realize that these waves in fact represent light; thus, light travels at c.
Calling it the speed of light is a bit misleading, since it's actually the speed of every wave/massless particle (such as gluons and gravitons). Gravitational waves also propagate at c, which means that if the Sun suddenly vanished, we would still orbit around it as long as it appeared in the sky (~8.3 minutes).

Einstein realized that c, or the velocity of waves in a vacuum, was constant irrelevant of the observer (stationary or moving at constant velocity). If you build your physical laws upon that premise, you get equations which yield "weird" results the closer you get to the speed of light, such as an exponential amount of energy needed to accelerate, time dilation, length contraction, relative simultaneity, and various related paradoxes.



This video greatly shows the visual implications (Terrell rotation+redshifting) around the fact that c is constant in every inertial frame -- in other words, how space and time get warped to keep c constant. Too bad the quality is kinda bad, but still.

[Deleted]

what happens if there are more than 2 objects moving in all kind of different directions?

The same thing that happens when you try to check the speed of something not going straight past a radar but rather at an angle. The speed appears to decrease as the radar (at least those here) measures the time it takes for the car to go from a point to pass in front of it and then calculates its speed.

If you go at an angle, it would appear that the speed decreases as it takes longer for the car to pass in front of the radar. So, in our example, saying you're in an object moving at the speed of light and you have another moving at a 45 degree angle to your path in the opposite direction (I used that since it basically makes it easy as a 45 degree is half of being perpendicular) if you attempt to measure the speed of the other thing right as you pass it, it would appear as 1.5 light speed technically.

This is why, overall, radars stand still right next to the street. Because if they moved with the radar or stood at an angle to the street without proper calibration, it would skew the results. Now, considering that I am unsure of exactly what happens when going over light speed (time slows down, sure, but it the slowing full? Does it reach total stop? Then how would light travel?) and right now I don't have time to check, I am not sure the logic regarding light speed is the same as that when comparing two moving cars due to the influence of time distortion.

[Aphrel]

If movement is relative, then if you have one thing moving the speed of light one way, and another thing moving the speed of light the exact opposite way, than the truth is relativity means that nothing can go faster than TWICE the speed of light, since the gap between those two would be created at twice the speed of light.

Ever heard of a guy named Einstein and his famous theory of realtivity? He kinda went indepth with this thing...

[Deleted]

Now, considering that I am unsure of exactly what happens when going over light speed (time slows down, sure, but it the slowing full? Does it reach total stop? Then how would light travel?) and right now I don't have time to check, I am not sure the logic regarding light speed is the same as that when comparing two moving cars due to the influence of time distortion.

We can't tell for sure because our laws stop working the moment you take v >= c for any particle with a non-zero rest mass. Hypothetically, using time dilation, an object moving faster and faster will appear to have a slower passing of time the closer it gets to c. Once it hits c (physically impossible), its clock should stop running. If it goes over c (impossible again), its clock should run with an imaginary time considering you get a negative in the root, for which we have no clue what it implies -- http://www.physlink.com/education/askexperts/ae283.cfm

[krunksmash]

If movement is relative, then if you have one thing moving the speed of light one way, and another thing moving the speed of light the exact opposite way, than the truth is relativity means that nothing can go faster than TWICE the speed of light, since the gap between those two would be created at twice the speed of light.

Wrong the gap is expanding at the speed of light. the difference is the gap is expanding in two directions from the start point. the two runners will always be moving apart at the speed of light NEVER any faster.