Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] geometry of spacetime (was: relativisitic mass ...)



Bob S wrote:

John M wrote:

The fact that that object *appears* to another observer to
asymptotically approach the speed of light is the *observer's*
problem!

Whatever this means, is it not in the same way the "object's" problem that
the left behind observer "appears" to asymptotically approach the speed of
light?

We understand that speed is a relative quantity and that the idea of an
"intrinsic" speed is without meaning or use. So what's the point?

I agree with most of what you and John D have had to say about my remarks, but I think there IS an important point to be made by noting that relativity places no MEANINGFUL limits on travelers. In fact, quite the contrary.

For instance, a person starting from rest and moving for 25 years with a constant and PERFECTLY comfortable acceleration of 1 light year per year squared (one "light per year"?), travels a little over 300 light years in a Newtonian universe. In a relativistic universe a stationary observer would determine that the same person travels not quite 25 light years.

Both of these distances are overwhelmingly meager compared to the size even of JUST our own galaxy, they barely get us to a few other stars, but the relativistic result looks most discouraging. It seems to bolster the idea that there is a fundamental "speed limit" imposed by relativity and I think many have internalized that idea to the point that statements like "things get harder to accelerate" acquire far more cachet than they deserve.

To counter this notion, I like to point out that the traveler him or herself can reach objects over 30 billion light years away, about twice the size of the entire observable universe by accelerating at that same rate for 25 years as measured by his or her own clocks.

See <http://www.csupomona.edu/~ajm/professional/talks/atgtc.pdf> for a not very elegant look at these issues.

--
John "Slo" Mallinckrodt

Professor of Physics, Cal Poly Pomona
<http://www.csupomona.edu/~ajm>

and

Lead Guitarist, Out-Laws of Physics
<http://www.csupomona.edu/~hsleff/OoPs.html>