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from ExplorationsScienceWithMichioKaku Website
Some scientists tend to scoff at the idea of interstellar travel because of the enormous distances that separate the stars. According to Special Relativity (1905), no usable information can travel faster than light locally, and hence it would take centuries to millennia for an extra-terrestrial civilization to travel between the stars.
Even the familiar stars we see at night
are about 50 to 100 light years from us, and our galaxy is 100,000
light years across. The nearest galaxy is 2 million light years from
us. The critics say that the universe is simply too big for
interstellar travel to be practical.
In addition, perhaps 99% of all sightings of UFO’s can be dismissed as being caused by familiar phenomena, such as the planet Venus, swamp gas (which can glow in the dark under certain conditions), meteors, satellites, weather balloons, even radar echoes that bounce off mountains.
(What is disturbing, to a physicist
however, is the remaining 1% of these sightings, which are
multiple sightings made by multiple methods of observations. Some of
the most intriguing sightings have been made by seasoned pilots and
passengers aboard air line flights which have also been tracked by
radar and have been videotaped. Sightings like this are harder to
dismiss.)
Within the Milky Way galaxy alone, there are over 100 billion stars, and there are an uncountable number of galaxies in the universe. About half of the stars we see in the heavens are double stars, probably making them unsuitable for intelligent life, but the remaining half probably have solar systems somewhat similar to ours.
Although none of the over 100 extra-solar planets so far discovered in deep space resemble ours, it is inevitable, many scientists believe, that one day we will discover small, earth-like planets which have liquid water (the “universal solvent” which made possible the first DNA perhaps 3.5 billion years ago in the oceans).
The discovery of earth-like planets may
take place within 20 years, when NASA intends to launch the space
interferometry satellite into orbit which may be sensitive enough to
detect small planets orbiting other stars.
The SETI project (the search for extra-terrestrial intelligence) has yet to produce any reproducible evidence of intelligent life in the universe from such earth-like planets, but the matter still deserves serious scientific analysis.
The key is to reanalyze the objection to
faster-than-light travel.
The first realistic attempt to analyze extra-terrestrial civilizations from the point of view of the laws of physics and the laws of thermodynamics was by Russian astrophysicist Nicolai Kardashev.
He based his ranking of possible civilizations on the basis of total energy output which could be quantified and used as a guide to explore the dynamics of advanced civilizations:
A Type I civilization would be able to manipulate truly planetary energies.
They might, for example, control or
modify their weather. They would have the power to manipulate
planetary phenomena, such as hurricanes, which can release the
energy of hundreds of hydrogen bombs. Perhaps volcanoes or even
earthquakes may be altered by such a civilization.
Growing at the average rate of about 3%
per year, however, one may calculate that our own civilization may
attain Type I status in about 100-200 years, Type II status in a few
thousand years, and Type III status in about 100,000 to a million
years. These time scales are insignificant when compared with the
universe itself.
Propulsion systems may be ranked by two quantities:
Specific impulse equals thrust multiplied by the time over which the thrust acts.
At present, almost all our rockets are based on chemical reactions. We see that chemical rockets have the smallest specific impulse, since they only operate for a few minutes.
Their thrust may be measured in millions
of pounds, but they operate for such a small duration that their
specific impulse is quite small.
For example, an ion engine which ejects
cesium ions may have the thrust of a few ounces, but in deep space
they may reach great velocities over a period of time since they can
operate continuously. They make up in time what they lose in thrust.
Eventually, long-haul missions between planets may be conducted by
ion engines.
Ram-jet fusion engines have an even larger specific impulse, operating for years by consuming the free hydrogen found in deep space. However, it may take decades before fusion power is harnessed commercially on earth, and the proton-proton fusion process of a ram-jet fusion engine may take even more time to develop, perhaps a century or more.
Laser or photonic engines, because they might be propelled by laser beams inflating a gigantic sail, may have even larger specific impulses. One can envision huge laser batteries placed on the moon which generate large laser beams which then push a laser sail in outer space.
This technology, which depends on
operating large bases on the moon, is probably many centuries away.
However, anti-matter is an exotic form
of matter which is extremely expensive to produce. The atom smasher
at CERN, outside Geneva, is barely able to make tiny samples of
anti-hydrogen gas (anti-electrons circling around anti-protons). It
may take many centuries to millennia to bring down the cost so that
it can be used for space flight.
Such a civilization might send tiny robot von Neumann probes to distant moons, where they will create large factories to reproduce millions of copies of themselves.
Such a von Neumann probe need only be the size of bread-box, using sophisticated nano technology to make atomic-sized circuitry and computers. Then these copies take off to land on other distant moons and start the process all over again. Such probes may then wait on distant moons, waiting for a primitive Type 0 civilization to mature into a Type I civilization, which would then be interesting to them.
(There is the small but distinct
possibility that one such probe landed on our own moon billions of
years ago by a passing space-faring civilization. This, in fact, is
the basis of the movie 2001, perhaps the most realistic portrayal of
contact with extra-terrestrial intelligence.)
Hence, Type 0,I, and II civilizations probably can send probes or colonies only to within a few hundred light years of their home planet. Even with von Neumann probes, the best that a Type II civilization can achieve is to create a large sphere of billions of self-replicating probes expanding just below the speed of light.
To break the light barrier, one must
utilize General Relativity and the quantum theory. This requires
energies which are available for very advanced Type II civilization
or, more likely, a Type III civilization.
But once the rocket arrives at its
destination and clocks are compared, it appears as if the rocket
went faster than light because it warped space and time globally,
either by taking a shortcut, or by stretching and contracting space.
Centrifugal force prevents the spinning ring from collapsing. Anyone passing through the ring would not be ripped apart, but would wind up on an entirely different part of the universe.
This resembles the Looking Glass of Alice, with the rim of the Looking Glass being the black hole, and the mirror being the wormhole. Another method might be to tease apart a wormhole from the “quantum foam” which physicists believe makes up the fabric of space and time at the Planck length (10 to the minus 33 centimeters - 10-33).
The second possibility is to use large amounts of energy to continuously stretch space and time (i.e. contracting the space in front of you, and expanding the space behind you).
Since only empty space is contracting or expanding, one may exceed the speed of light in this fashion. (Empty space can warp space faster than light. For example, the Big Bang expanded much faster than the speed of light.)
The problem with this approach, again, is that vast amounts of energy are required, making it feasible for only a Type III civilization.
Energy scales for all these proposals
are on the order of the Planck energy (10 to the 19 billion electron
volts, which is a quadrillion times larger than our most powerful
atom smasher).
For these extreme energy domains,
quantum effects will dominate over classical gravitational effects,
and one must go to a “unified field theory” of quantum gravity.
Because the theory is defined in 10 or
11 dimensional hyperspace, it introduces a new cosmological picture:
that our universe is a bubble or membrane floating in a much larger
multiverse or megaverse of
bubble-universes.
Within the next few years or perhaps within a decade, many physicists believe that string theory will mature to the point where it can answer these fundamental questions about space and time. The problem is well-defined.
Unfortunately, even though the leading scientists on the planet are working on the theory, no one on earth is smart enough to solve the superstring equations.
However, to go faster than light, one must go beyond Special Relativity to General Relativity and the quantum theory. Therefore, one cannot rule out interstellar travel if an advanced civilization can attain enough energy to destabilize space and time.
Perhaps only a Type III civilization can harness the Planck energy, the energy at which space and time become unstable.
Various proposals have been given to exceed the light barrier (including wormholes and stretched or warped space) but all of them require energies found only in Type III galactic civilizations.
On a mathematical level, ultimately, we
must wait for a fully quantum mechanical theory of gravity (such as
superstring theory) to answer these fundamental questions, such as
whether wormholes can be created and whether they are stable enough
to allow for interstellar travel.
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