Planets of Other Stars III

Getting There Quickly

Index

When Einstein linked space, time and gravity the way to Warp space-time was implicit in his equations. Very quickly the first "wormhole" solution was found to his equations, and the Einstein-Rosen Bridge was born.

But researchers in the 1950s and 60s quickly showed that the wormhole solutions were unstable, collapsing quicker than even light. At roughly the same time new solutions were found and the "Black Hole" was born. Some "Black Hole" solutions seemed to form stable wormholes within their mysterious "event horizons" - a ring of infinitely dense mass would rip a flaw into space-time, linking Universes or far-flung parts of one universe.

By the late 1970s such Kerr-Newman Black Hole wormholes were shown to be unstable. Accelerated mightily by the ring singularity surrounding the wormhole any mass falling in would send out space-time distortions, gravity waves, that would close the wormhole before it could be accessed. Once again another bridge across space-time was closed.

However several general relativists, led by Kip Thorne and inspired by Carl Sagan, sought out new wormhole solutions in the 1980s that could be traversed by masses, even masses as frail as humans. By threading the throats of their wormholes with "exotic matter" they found that links across space - and maybe time - could be maintained. A diverse bestiary of wormhole solutions were discovered - cubes, pyramids, discs and so forth. Some claimed that these could be used to build time machines, while others claimed that Nature abhors time travel and actively destroyed any path that might thread back on itself through time.

The question most people ask now that wormholes are respectable objects of research is how and when... which presently can't be answered. The energies required are daunting, but we don't yet know everything there is to know about gravity and space-time to truly say for sure. But before I boldly go there let's explore another issue... nullifying the effects of acceleration, which is related to the above in surprising ways.

What is Inertia?

Matter resists motion. Or rather, it resists any changes in its motion, any accelerations. To change an object's motion takes force and the expenditure of energy over the distance that the change in motion occurs. What is the source of this resistance? Newton and Galileo accepted inertia as an unexplained fact, but the development of electromagnetic and quantum theory has perhaps led to a deeper insight. What if inertia is caused by space itself resisting the change in the fields of the mass involved? Every particle of normal matter has fields other than gravity - electromagnetic and nuclear forces. Space itself is filled with virtual fields thanks to the Heisenberg Uncertainty relations - there is no such thing as "empty space" in a quantum field. So as a particle is accelerated its fields interact with the virtual fields of space to create a reaction force, inertia. This theory of inertia has been developed extensively by several physicists, notably Bernard Haisch. Could inertia then be controlled? As yet no one knows how, but let's look at the forces that hold the Universe together.

Forces and Fields

table 1 - forces of Nature

?

A major puzzle in physics is the relationship of the various forces and fields in Nature. Currently four forces are known, with a possible "mass-creating" field associated with them (see table 1.) In the 1920s Klein unified electromagnetism and gravity by hypothesising a fourth spatial dimension through which particles vibrated - this created the known properties of the electromagnetic field. This fourth dimension was incredibly small - far smaller than an atom - but by moving in that dimension particles created the electromagnetic field. Because the other forces were unknown in the 1920s physics soon superseded Klein's theory. But in the 1970s and 1980s interest was revived in the ability of tiny other dimensions to unify the forces of nature. Until this time fundamental particles had been described in quantum mechanics as POINT particles, since physically extended particle models could not reproduce known physics. However such a model collapses into? mathematical absurdity as the scale is reduced to the PLANCK LENGTH - the scale at which space-time itself is unstable due to quantum fluctuations.

A possible solution was found in SUPERSTRING THEORY which proposes that fundamental particles aren't points, but are in fact tiny one-dimensional "strings". The "Super" part of "Superstring" refers to the mathematical structure used to describe the forces which the strings generate as they vibrate in the curled-up higher spatial dimensions. To reproduce known particles and forces the number of dimensions is constrained to ten - 3 large (maybe infinite), 1 time (maybe infinite), and 7 curled up. Because the higher dimensions are curled up in a specific way, forming a Calabi-Yau manifold - the vibrations of the strings that compose ultimate particles are constrained to specific "harmonies" of vibration. In a sense particles are the "notes" that can be played in space-time. But in recent years the size of the curled up dimensions have been questioned.

At first physicists assumed the tiny dimensions were curled up at the Planck Scale - about 10^-35 metres - and so superstring energies were at the fantasic energy level of 10^19 GeV - ten million trillion times the mass of a proton (proton mass ~ 1 GeV, a convenient measure of energy, since mass and energy are equivalent.) This energy scale is far beyond the 1,000 or so GeV that particle accelerators can energise particles to, and this led many to think superstrings would be forever beyond direct testing experimentally. However some began studying mathematically what would happen if the dimensions were of different sizes. To their surprise the dimensions for the weak, electromagnetic and colour forces could be MUCH larger - at 10^-19 metres, which reduces the energy scale of their Unification from an incredible 10^16 GeV, to within about 10,000 GeV. This is just beyond current accelerator energies - we could be on the verge of unifying three of the Universe's forces. But what about gravity?

At first it seemed that gravity could be generated by dimensions as large as a millimetre, and still not be noticed by current experimental systems!

However the interiors of stars can be explored indirectly by their self-destruction in supernova explosions. These occur when a very massive star fuses its core into iron. Stars exist in a dynamic balance between compression by gravity and the energy of fusing particles in their cores. An iron core is a catastrophe since iron takes more energy to create than it releases in nuclear fusion. When enough iron is produced the core is forced by the weight of the outer layers of the star into catastrophic collapse. The outer core collapses onto the inner core which sends a shock-wave outwards through the rest of the star. Immense amounts of gravitational energy is converted into fused particles heavier than iron, and a multitude of neutrinos - by-products of weak-force nuclear reactions involved in creating elements and neutrons. The explosion in 1987 of a nearby supernova allowed physicists to refine their models of supernova explosions, and by this severely constrain the kinds of graviton<->particle interactions that could draw-off energy from neutrino production and creation of heavy elements. Thus, researchers conclude, the gravitational vibrations of strings occur on a scale much smaller than a millimetre, though no one yet knows how small.

So what does this mean for interstellar travel?

Unlimited Power?

Earlier I asked: Are there any power sources better than fusion energy?

Perhaps GUT energy - GUT stands for Grand Unification Theory, which describes the hypothetical unification of three of the natural forces.If we could push some seed-matter to GUT conditions we might be able to tap into the raw power of Creation itself, restarting the Big Bang in minature. In its very earliest phases the Universe is believed to have undergone a time of exponential expansion powered by matter-energy created by a GUT "phase transition". If the GUT energy scale is about 10^16 GeV, then it might forever remain beyond our abilities. But if the unification scale is much larger - say 10^-19 metres - then its achievement might be just around the corner.

With GUT energy, propellant - any old matter will do - could be pushed very close to lightspeed without the need for immense amounts of fuel for generating power for an accelerator system. Imagine if propellant could be accelerated to 0.995 c, then its relativistic "mass" is ten times its rest mass, so it is effectively ten times more propellant...

Imagine starships with GUT reactors - they launch with partially filled tanks in the Inner Solar System, then fly out to the Oort Cloud and latch onto a "small" comet. With the immense power of a GUT reactor they can then accelerate up to as close to lightspeed as desired. But is there anyway that we might accelerate to such speeds faster without suffering the effects of high acceleration?

Space Drives?

A "space drive" is an old science fiction idea which uses the analogy of free-fall to describe a propulsion system with high acceleration but without crushing "gee forces". Inertia hasn't been neutralised, just by-passed or "damped" [aka Star Trek...] When an object falls freely no "gee forces" are felt even at immense acceleration - with one caveat. When the gravitational source is large the rate at which gravity changes as you fall is minimal. But neutron stars and black holes have very "steep" gravitational fields that change rapidly. In such a situation the change in acceleration is felt as tidal forces, and these can be intense near very dense objects. Otherwise no forces are perceived while falling.

Hence a "space drive" could be described as "falling free" towards a "travelling" gravitational source. Or it could also involve using space itself as your propulsion system, so all the particles within the ship are accelerated evenly? How could this be achieved? Yoshiro Minami speculates that a very intense electromagnetic field could "pinch" space, and on release accelerate a space vehicle. However the magnetic fields involved are incredibly intense - 90 billion Tesla. A Tesla field creates a one newton force between magnetic fields separated by a metre - the Earth's field is much weaker, and not even neutron stars achieve the field intensity Minami's drive requires.

Minami suggests that other fields in space could be manipulated - perhaps the Higgs field, which creates the mass that each particle has. Hence by "pinching space" via the Higgs field very high accelerations without gee forces could be produced. With GUT Unification perhaps occurring at lower energies than expected then perhaps manipulating the Higgs field won't be as difficult also?

Faster than Light?

If space can be "pinched" then can it be "warped"? Potentially this is the ultimate way to the stars using physics far beyond what we know about in any detail. In 1994 Miguel Alcubierre published a study of a "warped" space-time structure that travels faster-than-light, and yet obeys Einstein's "laws". How is this possible?

Einstein's theories of Relativity, Special and General, are based on two basic premises - that all physical systems are equivalent, and that all observe the speed of light to be the same. How does this work out in practice? Simplistically, physical systems - like spaceships and human bodies - are chiefly based on the electromagnetic forces of their constituent particles. The speed of disturbances in the electromagnetic field, such as pulses of light, are not based on any other factor than a physical ratio between the magnetic and electric components of the field. From our own experiences these don't change whether we are moving or not, falling freely or standing on the Earth - or else life would be very different. Hence what relativity means is that at a local level the fundamental relationships between particles, their forces, don't change regardless of what they are doing collectively. Since the forces are the "framework" that make up the particles this makes sense. Travelling "faster-than-light" would require a NEW framework...

But what applies to particles does not apply to space-time. Wrap a sphere of "normal space-time" containing a ship in a bubble of distorted space-time, then faster-than-light can be achieved. The "warp bubble" requires some unusual effects - in the direction of travel space must be collapsing into the bubble, and it must be expanding behind the bubble. This is somewhat like what space-time was doing in the early stages of the Big Bang, which might mean that it is achieveable by GUT technology. Or maybe not?

Several researchers have estimated that to create a two hundred metre wide warp-bubble would take about 6.2 x 10^62 kilograms of negative energy times the c-factor it is travelling at - a figure that dwarfs the known Universe by about a factor of 10 billion! And it's negative energy, which no one knows how to create in any quantity for any great length of time. Alternatively the bubble could be shrunk - the energy needed is related to the area of the bubble - to microscopic size. It would then be a pinched "throat" to a mini-Universe containing a ship, but no one yet knows if this is possible, and physically reasonable sizes for the bubble [~10^-19 metres] would still take twice the mass of Jupiter in negative energy.

Chris van den Broeck, who developed the micro-sized warp field suggests there are still great difficulties with his system, but for sub-light the warp has real potential - I suspect it is another possible space-drive, since within the bubble no acceleration effects are experienced. A starship could accelerate to arbitarily close to light-speed within an arbitary time.

Planets of Other Stars I

Planets of Other Stars II: Getting There

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