TIME TRAVEL 227
radiation inside the wormhole can become incredibly strong-strong
enough to kill you. But the "many worlds" interpretation solves this
problem. If the radiation goes into the time machine and is sent into
the past, it then enters a new universe; it cannot reenter the time machine again, and again, and again. This simply means that there are an
infinite number of universes, one for each cycle, and each cycle contains just one photon of radiation, not an infinite amount of radiation.
In 1997, the debate was clarified a bit when three physicists finally
proved that Hawking's program to ban time travel was inherently
flawed. Bernard Ray, Marek Radzikowski, and Robert Wald showed
that time travel was consistent with all the known laws of physics, except in one place. When traveling in time, all the potential problems
were concentrated at the event horizon (located near the entrance to
the wormhole). But the horizon is precisely where we expect Einstein's theory to break down and quantum effects to take over. The
problem is that whenever we try to calculate radiation effects as we enter a time machine, we have to use a theory that combines Einstein's
theory of general relativity with the quantum theory of radiation. But
whenever we naively try to marry these two theories, the resulting theory makes no sense: it yields a series of infinite answers that are meaningless.
This is where a theory of everything takes over. All problems of
traveling through a wormhole that have bedeviled physicists (e.g., the
stability of the wormhole, the radiation that might kill you, the closing
of the wormhole as you entered it) are concentrated at the event horizon, precisely where Einstein's theory made no sense.
Thus the key to understanding time travel is to understand the
physics of the event horizon, and only a theory of everything can explain this. This is the reason that most physicists today would agree
that one way to definitively settle the time travel question is to come up
with a complete theory of gravity and space-time.
A theory of everything would unite the four forces of the universe
and enable us to calculate what would happen when we entered a time
machine. Only a theory of everything could successfully calculate all
radiation inside the wormhole can become incredibly strong-strong
enough to kill you. But the "many worlds" interpretation solves this
problem. If the radiation goes into the time machine and is sent into
the past, it then enters a new universe; it cannot reenter the time machine again, and again, and again. This simply means that there are an
infinite number of universes, one for each cycle, and each cycle contains just one photon of radiation, not an infinite amount of radiation.
In 1997, the debate was clarified a bit when three physicists finally
proved that Hawking's program to ban time travel was inherently
flawed. Bernard Ray, Marek Radzikowski, and Robert Wald showed
that time travel was consistent with all the known laws of physics, except in one place. When traveling in time, all the potential problems
were concentrated at the event horizon (located near the entrance to
the wormhole). But the horizon is precisely where we expect Einstein's theory to break down and quantum effects to take over. The
problem is that whenever we try to calculate radiation effects as we enter a time machine, we have to use a theory that combines Einstein's
theory of general relativity with the quantum theory of radiation. But
whenever we naively try to marry these two theories, the resulting theory makes no sense: it yields a series of infinite answers that are meaningless.
This is where a theory of everything takes over. All problems of
traveling through a wormhole that have bedeviled physicists (e.g., the
stability of the wormhole, the radiation that might kill you, the closing
of the wormhole as you entered it) are concentrated at the event horizon, precisely where Einstein's theory made no sense.
Thus the key to understanding time travel is to understand the
physics of the event horizon, and only a theory of everything can explain this. This is the reason that most physicists today would agree
that one way to definitively settle the time travel question is to come up
with a complete theory of gravity and space-time.
A theory of everything would unite the four forces of the universe
and enable us to calculate what would happen when we entered a time
machine. Only a theory of everything could successfully calculate all