Will we ever… travel faster than the speed of light?
Einstein said it is impossible, but as Jennifer Ouellette explains some
scientists are still trying to break the cosmic speed limit – even if it
means bending the laws of physics.
It is impossible to travel faster than light, and certainly not desirable, as one's hat keeps blowing off."
Woody Allen, Side Effects
Last
summer, a small neutrino experiment in Europe called OPERA (Oscillation
Project with Emulsion tRacking Apparatus) stunned the world with a
preliminary announcement that it had clocked neutrinos travelling just a
few fractions of a second faster than the speed of light. The news even briefly overshadowed the far more recognizable Large Hadron Collider’s ongoing hunt for the Higgs boson.
Despite
careful hedging by scientists, the popular imagination jumped right
from neutrinos to a viable spacecraft for fast interstellar travel.
After all, the prospect of faster-than-light (FTL) travel has been a
science fiction staple for decades, from wormholes and Star Trek’s original warp drive, to the FTL “jumps” used to evade the Cylons in SyFy’s Battlestar Galactica
reboot. It takes years, decades, centuries even to cross the vast
expanses of space with our current propulsion technology – a realistic
depiction of the tedium of space travel in entertainment would likely
elicit the viewer equivalent of “Are we there yet?”
So the OPERA
announcement was bound to generate excitement, even if the neutrinos in
question were only moving nanoseconds faster than light – hardly
sufficient to outrun the Cylons, but nevertheless faster than c, the
cosmic speed limit set by Albert Einstein back in 1905.
Unfortunately, the euphoria was premature: the OPERA results were incorrect,
thanks to a calibration error. The culprit: a faulty cable connection
in the GPS system used to time the neutrinos along their journey. That
killjoy Einstein wins again.
But if the OPERA saga did tell us
anything, it’s that the idea of travelling faster than light continues
to capture the imagination. As Hollywood screenwriter Zack Stentz (Thor,
a.k.a. “Vikings in Space
”) said recently at a Los Angeles panel on the science of superheroes,
“Every science fiction writer who wants to get out of the solar system
[within a human lifetime] gloms onto that. It’s the leap of faith that
lets you tell stories on this bigger canvas.”
“You cannae change the laws of physics”
“Leap
of faith” is a particularly relevant phrase to use here. The fact is
we’ll never be able to travel beyond the speed of light, at least based
on our current understanding of established physics.
As any object
with mass accelerates – like a proton in the LHC – it gains energy,
always needing just a little bit more energy to accelerate even further.
The LHC, the largest and highest-energy particle accelerator we have,
boosts protons as close to the speed of light as we can get, but they
never quite hit the mark. If a proton did achieve that speed, it would
need infinite energy to go any faster, and we don’t have an infinite
supply of energy.
Equations don’t tend to lie, especially ones
that have been tested and re-tested in countless experiments for over a
century. For all practical intents and purposes, the speed of light is
an insurmountable threshold.
But physicists would never make any
progress at all if they threw in the towel quite that easily, and nobody
thinks Einstein will have the final word in perpetuity. Many scientists
are happy to consider the possibility of violations of relativistic
principles, even if none have yet been experimentally confirmed.
One of the earliest proposed possibilities for FTL travel involved a hypothetical particle called a tachyon,
capable of tunnelling past the speed of light barrier. This turned out
to be more of a mathematical artifact rather than an actual physical
particle.
However, another reason for all the OPERA-tic excitement
was that back in 1985, physicists proposed that some high-energy
neutrinos might really be tachyons,
capable of interacting with an as-yet-known field, giving them just
enough of an energy boost to break through the barrier. Such
tachyon-like neutrinos would supersede photons as the fastest particles
in the universe.
OPERA’s calibration error dashed
those hopes, but there are still plenty of potential loopholes to be
explored, such as the Star Trek-inspired warp drive mechanism first
proposed by Mexican physicist Miguel Alcubierre in 1994.
In general relativity, spacetime is dynamic, not static, warping and
bending in response to the presence of mass or energy. Alcubierre
suggested that it might be possible to encase a spaceship within a “warp
bubble”, whereby space contracted in front of the craft and expanded
behind it, enabling it to travel faster than light. But within that
bubble, spacetime would remain essentially flat and the craft would
technically “obey” the cosmic speed limit.
Alas, once again we
face an energy problem: achieving that degree of curvature would require
enormous amounts of energy – and negative energy at that – equivalent
to the mass of Jupiter. To propel a spacecraft across the Milky Way
galaxy may require more energy than can be found in the mass of the
entire universe. A more energy-efficient ring-shaped design
for such a warp drive was described recently at a symposium on
interstellar space flight, offering a meager shred of hope to diehard
space acolytes that for future generations, warp drive will be a
reality.
However, given what we know about general relativity and
quantum field theory, “It almost certainly can’t be done,” says Ken
Olum, a cosmologist at Tufts. “Of course, if we are talking about
quantum gravity, it’s hard to know, because we don’t really know what
that is.”
Former Nasa scientist Kevin Grazier,
who was the technical consultant for Battlestar Galactica, says that a
version of the Alcubierre warp drive inspired the “jump drive” used in
that series. It was based on the assumption that, in this fictional
world, the Colonials had merged theories of electromagnetism and
gravity, such that if you could create a very intense electromagnetic
field, it would be functionally equivalent to an intense gravitational
field capable of warping spacetime. Turning that ingenious fiction into a
viable reality is another matter altogether.
Brane gain
If
we really want to get speculative, Olum suggests FTL travel would be
possible if exotic concepts, like those that emerge from superstring
theory, prove to be correct.
We inhabit four-dimensional
spacetime, but various permutations of superstring theory suggest our
universe is just one of many, co-existing within a bubble of
five-dimensional spacetime called the “bulk.” Within that bulk, our
universe lines up in parallel with all the others, just like the pages
in a book. Olum explains that, hypothetically, one could take a shortcut
through the bulk, thereby arriving at your destination sooner than if
you had travelled along your four-dimensional surface, or brane (short
for membrane) as it is known.
Even then, there is a catch. “In
brane theories, only gravitons can travel through the bulk,” says Olum.
So one would need to invent a machine that could scan an object and
transmit the information in the form of gravitons to a second machine on
the other end which would then reconstruct that object – shades of
teleportation, only with gravitons.
Considering we have yet to observe gravitons in our most powerful accelerators, and the current record for teleporting
small clouds of atoms is the relatively non-Cylon-troubling distance of
143 kilometres (88 miles), this scenario must also remain firmly in the
realm of science fiction, at least for now. Science advances, but it
does so slowly, at a pace nowhere near the speed of light.
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