jdavel
- 617
- 1
StarThrower, I finally see the source of your confusion.
You correctly say that the postulates of SR imply two equations,
Equation 1:
\Delta t^\prime = \frac{\Delta t}{\sqrt{1-v^2/c^2}}
and Equation 2:
\Delta t = \frac{\Delta t^\prime}{\sqrt{1-v^2/c^2}}
If these weren't both true then there would be something fundamentally different between moving to the left and moving to the right. The postulates say there is no such difference.
But then you mistakenly say that these equations together imply a third equation,
Equation 3:
\frac{1}{\sqrt{1-v^2/c^2}} = \sqrt{1-v^2/c^2}
This simply (and obviously) isn't true.
The reason you can't get to Eq 3 from Eqs 1 & 2 is that the variables delta-t and delta-t' don't represent the same thing in Eq 1 that they do in Eq 2. So the ratio, delta-t/delta-t' in Eq 1 isn't the same as the ratio delta-t/delta-t' in Eq 2. In fact, they are exactly the reciprocals of each other! So your Eq 3 should read:
\frac{1}{\sqrt{1-v^2/c^2}} = \frac{1}{\sqrt{1-v^2/c^2}}
which is true, but not very interesting, and certainly no threat to the validity of SR!
You correctly say that the postulates of SR imply two equations,
Equation 1:
\Delta t^\prime = \frac{\Delta t}{\sqrt{1-v^2/c^2}}
and Equation 2:
\Delta t = \frac{\Delta t^\prime}{\sqrt{1-v^2/c^2}}
If these weren't both true then there would be something fundamentally different between moving to the left and moving to the right. The postulates say there is no such difference.
But then you mistakenly say that these equations together imply a third equation,
Equation 3:
\frac{1}{\sqrt{1-v^2/c^2}} = \sqrt{1-v^2/c^2}
This simply (and obviously) isn't true.
The reason you can't get to Eq 3 from Eqs 1 & 2 is that the variables delta-t and delta-t' don't represent the same thing in Eq 1 that they do in Eq 2. So the ratio, delta-t/delta-t' in Eq 1 isn't the same as the ratio delta-t/delta-t' in Eq 2. In fact, they are exactly the reciprocals of each other! So your Eq 3 should read:
\frac{1}{\sqrt{1-v^2/c^2}} = \frac{1}{\sqrt{1-v^2/c^2}}
which is true, but not very interesting, and certainly no threat to the validity of SR!
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