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# Special Relativity

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Ok, so I have been looking at special relativity in past few weeks, and I have noticed some weird things. Don''t worry, nothing to do with homework. so, we have Lorentz transforms: x'' = lambda(v)*(x - v*t) t'' = lambda(v)*(t - v*x/(c*c)) so, I consider the time dilation aspect, and I find this on the net. It all seems to make sense in terms of what it says: x'' = ct'' x''^2 + v^2*t^2 = c^2*t^2 (Pythagorean theorem) c^2*t''^2 = c^2*t^2 - v^2*t^2 t'' = t*lambda(v) which seems well and good except: t'' = lambda(v) * (1 - v/c)*t which means, 1-v/c =1 => v=0 which can''t be! So whats the problem? Am I misunderstanding something? Other than that, if two objects are moving relative to each other at a velocity, then without using any "external" knowledge we know only 2 things: 1. The magnitude of their relative velocity. 2. A sign indicating weither they are heading towards or away from each other. We do not know the DIFFERENCE between their velocities. The traditional relative velocity calculation involving subtraction of two velocities is not available in the vacuum. Because, both the velocities have to be computed relative to the ONLY other object. And, this is one thing that special relativity does not seem to take into account. IMHO, if this were taken into account, there is no possible way to say which object faces time dilation. Please correct me if I am wrong (which I probably am, considering I am not a genius). SporadicFire.

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How did you get this:

x'' = ct''

From this I get x = c * t, which is nonsense.

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From what I gather, it is one of Einstein''s assumptions
actually... the speed
of light is the same in all frames of reference. This
implies both:

x=ct
and x=ct''

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But I think x is the position of an object, not the light, and v is the velocity of the same object. And the light''s velocity is c. So I think x=c*t is wrong.
But ask the physicist (13rd post) in the gravity topic.

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Actually, I am quite certain of this. x is the position of
the light wave with respect to the first frame of reference,
and x'' is the position of the light wave with respect to
the second frame of reference. The definition is the
same for both the lorentz transform and the stuff that
I found on the web. Hopefully the physicists will soon be
attracted to this topic.

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check your work more carefully, make sure you''re not making a <i><b>stupid</i></b> assumption

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The whole point of this post is to find out what the stupid assumption is. Because, being a newb at this, I really
do not know.

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x is the position of an event in a linear frame of reference which has velocity v. It is NOT the position of light. x'' is the position of the same event in a different linear frame of reference which has velocity v''.

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I guess this means I have misunderstood alot. So how does it really work? How is length contraction/time dilation really computed?

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