UNBC Life

Future Under the Magnifying Glass
Part 1: Time Machine

Mani Samani & Nahid Taheri
Contributors

[: George Jones, a senior lab
instructor in UNBC's physics
department, sat down with two Over
the Edge volunteers to answer our
questions about the future.

Question: Can we travel to the future?

Answer: In theory, yes. According

to the theory of relativity, one can
suppose an astronaut leaves Earth,
travels at 99.9% the speed of light,
and returns to Earth. If the astronaut
ages ten years during the trip, the
Earth and the people on it will have
aged 274 years, so the astronaut will
have traveled into the future! | might
be dead and my grandchildren might
be alive. That is clearly allowed with
the laws of physics and we have
measured it small amounts of time
travel. In fact, this is taken into account
whenever we use GPS. GPS satellites
orbit about 20,000 kilometers above
the earth. Due to their orbital speed
and height, clocks on these satellites
run at different rates than identical
clocks on the Earth. If
this were not
taken into

account,

large errors (11 kilometers per day!) in
positions predicted by GPS devices
would accumulate.

Question: How about travel to the
past?

Answer: We just pln
do not know.

Stephen

Hawking st —
wrote a

famous

paper in 1992

in which he

called the "Chronology
Protection Conjecture,” what he
said would make the world sate for
the historian. History would not be
screwed up as long as there is no time
machine. This is a standard paradox;
what if one goes back in time, and
one kills your grandmother before
your parents were born? How is that
possible? If we do not have time
machines we do not have paradoxes
like that. So Stephen Hawkings 1992
conjecture proves that we do not
have time machines. However, using
space-time wormholes, backwards
time travel may be possible. In
Einstein's theory of general of
relativity, space-time is warped.
Space-time wormholes first
generated substantial interest
in the physics community in
1988. Physicists soon realized
that if space-time wormholes
exist, then they could be used
to create time machines. We,
however, currently have zero
experimental evidence for

wordpress.com

k space-time wormholes. In 1992,

Stephen
Hawking showed that quantum theory
might prevent the formation of time
machines by creating a burst of very
high energy radiation just before any
time machine forms, thus destroying
the apparatus. In 1997, further work
suggested that a full quantum theory
of gravity is needed to resolve these
questions.

Question: Is there any investigation into
travelling to the future?

Answer: One has to travel very fast in
order to do this. We have not travelled
nearly fast enough to verify this. You
have to travel near to the speed of
light which is 300,000 km/s. What is
the fastest soeed a human being has
ever gone with respect fo the earth?
| think it is 1] km/s, which is not very
much compared to the speed of light,
and this was the speed achieved by
the humans when they went to the
moon. We really have not travelled
fast enough with humans. We just have
not done that, and there is not anyone
even close fo doing that; not in the
next fitty years, or even in the next five
hundred years. | do not think we can
get to the future like that. However we
have some very accurate clocks,
SN such as atomic clocks. In 1971,
Ae scientists put an atomic clock
“Fin two airplanes, and flew
them in ditferent directions
around the world. The clocks
were synchronized, and
when the planes landed,
there was a measurable
ditference in the readings!

Question: If we had the
ability to travel into the
future, what destination should
we travel to?

18

onco™

ail"

Answer: Destination is not important.
Just the fact that you can go and come
back; the speed related to us on the
earth is important.

Question: When you look at the sky
you look at the history, so is it possible
to look at the past

Answer: It is possible to look at the
history of stars, but not the history of
humans. For example when you look at
the sun we are looking at it as it was
eight minutes ago; when we look at
the next near star we see it as it was
four years ago; when we look at a
star from another galaxy we see it as
it was millions or billions of years ago.
We cannot see ourselves in the same
context. Going back to the question:
in theory, in some universes, yes. If the
universe is closed, and if the universe
expands not too slowly and not too
quickly, we can see all the way in the
universe, and can observe an image
of the Earth in the distant past. There
are no paradoxes associated with
this. We do not know if our universe

is closed, and our universe seems fo
be expanding too quickly for this to
happen. We cannot be completely sure
that the universe's rate of expansion
will not slow down in the future.

Ouestion: Could you please introduce
some more references for if anyone
would like to read more about this
topic?

Answer: There are two books which
are not just for physicists; everybody
can read them. They are Time
Machines by Paul JINahin and Time
Travel and Warp Drives by Allen
Everett and Thomas Roman. There

is also a less accessible book titled
Lorentzian Wormholes by Matt Visser.