A Time Travel Dialogue

1) How do I become a normalist? 2) If time travel was
possible how come we don't see time travelers from the
future?

The objection to time travel you raised is a strong empirical
argument that I used to use, but is outweighed by stronger
logical arguments based on the possibility of altering the 
past (an implication of normalism). Assuming the physics is
correct, there are many reasons why we have not encountered
time travelers. First, it is much easier to send small
particles back in time than objects as massive as ourselves.
Secondly, the needed acceleration might have to be provided
by a strong gravitational field such as a black hole. If Tb
is not reached, the time travelers will never escape the hole
into past time. Thirdly, the physics does not predict the
possibility of travel back to the future, so one could be
trapped in the past. Fourthly, it is easier to go to the
recent past than the remote past, so that we may be a
difficult destination when the technical problems are
overcome. These, and other technological factors, may
discourage people from ever making the attempt. .

How to become a normalist? Study the website, flip over all
decisions (no deliberating), assume nothing as to the future,
or the present, or the past, and act accordingly. The result
is called your nature.

I am a firm believer that just about anything is possible
with a particle. When talking about time travel most people
assume it involves sending humans through time on earth and
then back to the future. Sending an atom back 10ms in a black
hole is not very glamorous.

Human beings could go back. But the risk is commensurate with
the reward, so people may not want to try. But . . . the real
reason that there are no time travelers among us is that the 
future does not exist, in any sense, at any time. The paradox
is strong, and satisfying.

This is a brilliant argument. I can't believe I didn't think
of it. I should be studying more normalism. I would think
that if people can't return to the future they would want to
go back only a short distance to prevent an accident or make
money on the stock market. $100,000 is Microsoft options in
1983 would be worth $150 billion today.

To say the future does not exist is to say you can only go
back in time (a position that Hawking has apparently adopted,
for different reasons) , which, again, may be costly (because
of induced g-fields as Tb is approached). And as to
normalism and the market--it obviates the need. Also, without 
actually doing the calculations, the process of accelerating large 
masses (e.g., Americans) back into time could consume the
present universe, which is a (logically) nice concept.

It actually might be happening all the time, as objects
accelerate into black holes, and we don't notice it because
of the scale on which it is occuring, so that the universe
can be described as a density of spacetime strings vibrating
with only the present as a fixed or nodal point. Each string
would extend back to the beginning of time (big bang or
whatever), with harmonics concentrated in the recent past.
(This could/should turn out to be relatable to conventional
string theory--but is not the same). The real point is that,
like Planck's black body analysis, we may be able to say that
time is quantized backwards, and that is why the universe
hasn't collapsed.