Light and Time

[JacobEvans]

Quick question.

My physics teacher told me that according to ToR, while we observe light from the sun as taking 8 or so minutes to arrive on Earth, from the light's perspective it would appear to have arrived instantly. Basically t=0s ???

Is this correct?

 

[Master_Ghost_Knight]

Yes. For it the time doesn't pass.

 

[ImprobableJoe]

Quick question.

My physics teacher told me that according to ToR, while we observe light from the sun as taking 8 or so minutes to arrive on Earth, from the light's perspective it would appear to have arrived instantly. Basically t=0s ???

Is this correct?

Light doesn't wear a watch... :lol:

 

[Neffi]

Well is that the right way to put it? Light, traveling at C doesn't experience time at all, so can it even 'understand' "instantly"?

 

[GoodKat]

Well is that the right way to put it? Light, traveling at C doesn't experience time at all, so can it even 'understand' "instantly"?

Light isn't conscious.

 

[COMMUNIST FLISK]

where c is the speed of light in a vaccuum
v is the velocity of said object/particle
t is the "real" time relative to the object
t0 is the observed or "real" time (observed by the person relative to the motion of said object)

 

[King of NH]

:?: I was hoping to find some sources to cite, but I can't seem to find them now, so if anybody can help out?

Okay, there is a type of particle that is formed when high energy strikes our upper atmosphere. This particle is extremely short lived, far too short lived to reach the ground even at the speed of light.

Now, if it cannot possibly travel from the upper atmosphere in its short life without defying the laws of physics, it should be hard to find, right?

But that's the problem. They are easy to find. They are striking you right now.

No, they do not defy the laws of physics but rather prove the laws of physics. The particle is short lived at rest, when the life span is measured in a lab. But as the particle moves closer to the speed of light, time slows for that particle. What is less than a millisecond for the particle is much longer for us, long enough for the particle to reach us before it dies.

So, yes. As objects move faster, time slows.

 

[Pulsar]

:?: I was hoping to find some sources to cite, but I can't seem to find them now, so if anybody can help out?

Muon decay.

 

[JacobEvans]

Thanks guys! I think this is starting get easier to comprehend!

 

[scikidus]

Using the time-dilation forumula posted above, an object moving at the speed of light would experience time dilation of

Well, 1/0 is undefined, but it really means that there's an infinite amount of time dilation, and therefore time passes infinitely quickly (using the term "infinite" loosely, of course).

 

[COMMUNIST FLISK]

Using the time-dilation forumula posted above, an object moving at the speed of light would experience time dilation of

Well, 1/0 is undefined, but it really means that there's an infinite amount of time dilation, and therefore time passes infinitely quickly (using the term "infinite" loosely, of course).

i take it as it takes unlimited time to get thier and thus appears to be motionless (to the view of the object travelling at the speed of light) ie to the object travelling at the speed of light, time stops.

there is also mass dilation (replace t and t0 with m and m0) and lenth contraction (replace t and t0 with L and L0, taking note that L = L0 TIMES the rest of the equation (not over it))

 

[JacobEvans]

i take it as it takes unlimited time to get thier and thus appears to be motionless (to the view of the object travelling at the speed of light) ie to the object travelling at the speed of light, time stops.

that would be true if it were 0/1 not 1/0

 

[scikidus]

that would be true if it were 0/1 not 1/0

This. Really, it takes 0 time to get anywhere, from the light's perspective. Also, the length contraction gives any object traveling at c a length of 0 and an infinite mass. infinite mass / 0 volume = black hole.

 

[aeroeng314]

infinite mass / 0 volume = black hole.

Not in this case. Especially since in the inertial frame of reference, the particle has the same inertial mass and length and doesn't form a black hole. In GR gravity is not just a function of mass and distance like in the Newtonian model, so you can't reason about it in that way. You have to solve the Einstein field equations for that particular case.

 

[COMMUNIST FLISK]

This. Really, it takes 0 time to get anywhere, from the light's perspective. Also, the length contraction gives any object traveling at c a length of 0 and an infinite mass. infinite mass / 0 volume = black hole.

ahhh my bad guys! was my equation right then? (did it from memory)

 

[scikidus]

Not in this case. Especially since in the inertial frame of reference, the particle has the same inertial mass and length and doesn't form a black hole. In GR gravity is not just a function of mass and distance like in the Newtonian model, so you can't reason about it in that way. You have to solve the Einstein field equations for that particular case.

OK then I have a question: does the person traveling really fast have any way to directly measure the relativistic mass? Doe she feel gravitation force from it?

 

[aeroeng314]

OK then I have a question: does the person traveling really fast have any way to directly measure the relativistic mass? Doe she feel gravitation force from it?

Of course not. Motion is not an absolute. If it were possible to make any such measurement, then there would be such a thing as an absolute reference frame. All of these relativistic effects can only be measured by an external observer. To the person "moving near the speed of light", what they really see is the rest of the universe moving, on average, near the speed of light. They would see the rest of the universe slow down, contract in the direction of motion, and increase in mass.

 

[Squawk]

Can I reccomend a book by the name of "The Elegant Universe" by Brian Green for anyone interested in a little reading on this. Strictly speaking it is a book on string theory, but talks at lengh on relativity and quantum mechanics.

The best explanation I heard on the time dilation thing was pretty much as follows.

We think of ourselves as traveling in two different ways, through the normal three dimensions of space and through on dimension of time. Rather than considering these two to be separate, consider instead the idea that we are traveling through 4 dimensional space-time.

Further, consider that we are always traveling through 4 dimensional space time at precisely the speed of light. If we are stationary in the three spatial dimensions then all that speed is through the 4th dimension of time. If we are traveling through the three spatial dimensions at the speed of light then we are stationary in the 4th dimension of time.

Any speed that we have through the spatial dimensions must be subtracted from our speed in the 4th dimension of space, and as such as you speed up in space you slow down in time. At the extremes, at stated, if you travel through time at the speed of light you are stationary in space, and if you travel though space at the speed of light you are stationary in time, but at all times you are traveling precisely at the speed of light through space-time.

This all follows from the observation that light always travels at the same speed from the point of view of any observer.

 

[Pulsar]

Not in this case. Especially since in the inertial frame of reference, the particle has the same inertial mass and length and doesn't form a black hole. In GR gravity is not just a function of mass and distance like in the Newtonian model, so you can't reason about it in that way. You have to solve the Einstein field equations for that particular case.

There's a similar thread about this: Quark ---> singularity.