Re: On Higher Dimensional Travel
- From: Rumpelstiltskin <PleaseDoNotReplyByEmail@xxxxxxxxxxx>
- Date: Wed, 12 Sep 2007 06:27:52 -0700
On Tue, 11 Sep 2007 22:56:14 -0700, Sir Frederick
<mmcneill@xxxxxxxxxxxx> wrote:
http://www.newscientist.com/blog/space/
Tuesday, September 11, 2007
Could we send 'instant' messages across the cosmos?
If we ever find an intelligent civilization elsewhere in the universe,
communication with it will likely be excruciatingly slow.
Suppose the alien planet was 100 light years away ? practically in our cosmic
backyard. When you factor in the light travel time, one would have to wait 200
years between each question and reply, making for very slow conversation.
In science-fiction universes like Star Trek, on the other hand, instant
communication across the galaxy is no problem at all. To do this, one would need
the ability to send signals faster than the speed of light, which apparently
runs up against Einstein's cosmic speed limit. Still, might there be a way to
accomplish this in the real universe?
There just might be, according to a study to be published in the journal
Physical Review D. Shortcuts through extra dimensions are the key, say Fabrice
Petit of the Belgian Ceramic Research Centre and Michael Sarrazin of the
Facultés Universitaires Notre-Dame de la Paix, both in Belgium.
Petit and Sarrazin describe a scenario inspired by string theory in which what
we think of as our universe is actually just one "sheet" in a higher dimensional
space-time. According to this picture, our universe actually includes a second
sheet that we do not normally notice because we are confined to our own sheet.
Such "braneworld" scenarios, where "brane" is short for membrane, are receiving
considerable attention from theoretical physicists these days because of their
potential to explain puzzling aspects of particle physics and cosmology.
For example, gravitons, the theoretical particles that carry the gravitational
force, might be able to leak into the space between branes ? which could explain
why gravity is so weak compared to other forces like electromagnetism.
Petit and Sarrazin describe a less well-studied scenario where the two branes
are all there is. In this case, particles cannot exist between the branes, but
they can hop back and forth between the sheets through the magic of quantum
mechanics, which allows particles to disappear and reappear in a new spot,
"tunnelling" across normally insurmountable barriers.
Under the right circumstances, a strong magnetic field can cause a particle to
"oscillate" between the two branes. If the other brane is warped in a certain
way, distances there may be shorter than in our own brane. This means if a
fast-moving particle were made to travel in the other brane for a while before
returning to ours, it could actually get to a distant part of our universe much
faster than a light signal confined to our brane.
For those of you hoping that we might make spaceships travel faster than light
this way, I have bad news. Petit and Sarrazin say their setup only works for
fermions ? particles that include protons and neutrons, but not all types of
atoms. Since our bodies contain a lot of atoms that are not fermions, humans
could never take such shortcuts.
But by making electrons or other fermionic particles take shortcuts through the
other brane, it might be possible to communicate faster than light speed, just
like in Star Trek.
The effect is similar to how light travels at a different speed in water
compared to in a vacuum, says Daniel Chung of the University of Wisconsin in
Madison, US, who has explored similar scenarios. "With that analogy, we are
living inside water, but if the light can leave the water and come back inside,
it can in principle reach the destination faster than if the light travelled
just in water," he says.
Previous work, like Chung's, has also considered the possibility of shortcuts
through extra dimensions (see At last, a way to test time travel, for example).
But most of this has focused on exotic particles like sterile neutrinos, which
could travel in the space between branes.
Niayesh Afshordi of the Perimeter Institute for Theoretical Physics in Waterloo,
Ontario, says Petit and Sarrazin's scenario has an advantage in that ordinary
particles like electrons can experience the shortcut effect, rather than just
exotic particles.
This all sounds very speculative. But Petit and Sarrazin say their idea can be
tested. "If the theory is founded, the particles should oscillate periodically
between the two sheets," Petit says. That means some of the neutrons could
vanish while travelling from their source to a detector, something that could be
measured.
Breaking the light speed barrier is normally thought to be impossible because it
allows particles to time travel, leading to "causality problems" ? the paradoxes
that arise when effects can precede their causes.
But Chung argues that they do not automatically violate causality. The particles
that take shortcuts get to their destination faster than light confined to our
brane does, he says. But when their path through the extra dimension is taken
into account, they still obey an overall speed limit, allowing causality to be
preserved.
Suppose that we could actually put this into practice and start communicating
with an alien civilisation. Assuming we couldn't send a lot of data all at once,
how should we start things off? What information would make the most sense to
start with? Physics equations? Music? Images of life on Earth?
I certainly don't want to discourage anybody from looking at this,
but in my opinion it's a lost cause due to the nature of reality. We
do already have some phenomena that appear to "travel faster
than light". One example is the instantaneously simultaneous
collapse of two entangled "waves" into matching particles
though the waves had traveled far from each other before the
collapse. Another is the phenomenon of effects appearing
before their causes could have reached them at the speed of
light. What is common to all such things is that they cannot
be reversed "after" they have happened because information to
reverse them cannot travel the distance between them in time
to cancel the cause of which they were the effects. Faster-
than-light travel would violate causality, as in the famous
whimsical thought-experiment of a man going back in time and
killing his father before his father could have any children.
I'm holding on to causality, and it will take a lot to make me
think it can be violated. A counter-point, though, is that the
"why" of the origin of the universe is such a perplexing and
even "irrational" problem that something outside the day-to-day
interactions of the universe encompassed by what we
currently know of physics must play a part.
The "branes" are a very interesting conjecture, but they
don't make any inroad on the "why" of existence, because
they just transfer the "why" the universe exists into a "why"
the branes exist. Anything that tries to explain existence
"starting" with nothing runs into the same roadblock - our
logic cannot make an inroad into the problem, in principle
not just in terms of what is known or guessed.
--
Posted via a free Usenet account from http://www.teranews.com
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