At 09:39 AM 4/1/2010, Stephen A. Lawrence wrote:
It's the fact that there's no side to side contraction which leads to
all the arguments over whether the contraction is "real". The
fore-and-aft contraction is arguably just a "trick of the light".
This whole universe is a "trick of the light." Eh?
It seems I'm becoming a budding, or blooming as the case may be,
science writer, so if I can explain this it would probably mean that
I understand it, at least sort-of. Here is my approach. I avoid math,
except for the concept that if an object is travelling from point A
toward point B (both stationary) at velocity v, and we compare the
time this travel takes with what it takes if point B is now
travelling toward A at the same velocity, we will find the latter
time to be half the former. They meet at the point which was the
original "middle," the half-way point between A and the initial position of B.
To apply this to relativistic velocities depends on the finding that
the speed of light (in a vacuum) does not vary with the velocity of
the observer.
That leads very directly to the expectation that time is dilated, for
example, I won't explain that here. But it has to do with how we
measure time (or experience time, which is quite the same thing, our
experience being a kind of measuring).
Here, the issue is how we measure distance. I'm going to use a
standard, for distance, of how far a beam of light travels in a
certain time. This is a constant no matter what the frequency of the light is.
Imagine a beam of light emitted from a source in our ("stationary")
frame of reference. The light beam is aimed toward the object from
the front. It passes through a hole in the middle of the object, from
front to back. We can see it and can measure the time that this beam
takes to travel from front to back.
An observer on the object can also observe this beam and can make the
same measurement. The measurement made within the object's frame
seems perfectly ordinary, and a spherical object will have the same
dimension in all directions (on a diameter).
However, to us, while the beam is passing from the front to the back,
we can see that the time is shorter, the faster the object is moving,
because, during the passage, the back of the object is approaching
the position that the front was in when the beam entered. As the
object approaches c in velocity, the time of travel approaches half
of the full time for a stationary object, because at c, (nevermind
the infinite blue shift), the back is travelling as fast as the light
beam, so they meet in half the time.
But there is a limit suggested by this, that the maximum flattening
is by one-half.
Well, folks, I didn't know that, and, in fact, my impression from pop
science had been otherwise, that objects would get flatter and
flatter, approaching zero thickness as they approach c. Is it true,
the limit, or did I miss something?
Is the flattening "real"? What does "real" mean? It can be measured,
just as time dilation can be measured. Is time dilation "real"?
(There is an explanation for time dilation that is even simpler, and
the experimental evidence for it is also simpler and more clear.)
