Part 9 (1/2)

Alcubierre speculates that a journey in his proposed starshi+p would resemble a journey taken on the Millenniuuess is they would probably see so very similar to that In front of the shi+p, the stars would beco-just black-because the light of the stars couldn't h to catch up with them,” he says

The key to the Alcubierre drive is the energy necessary to propel the spacecraft forward at faster-than-light velocities Nory in order to propel a starshi+p, which always travels slower than the speed of light To y so as to be able to travel faster than the speed of light one would need to change the fuel A straightforward calculation shows that you would need ”negative y,” perhaps the most exotic entities in the universe, if they exist Traditionally, physicists have disative mass as science fiction Butsee that they are indispensable for faster-than-light travel, and they ative matter in nature, but so far without success (Antis The first exists and has positive energy, but a reversed charge Negative ative hter than nothing In fact, it would float If negative matter existed in the early universe, it would have drifted into outer space Unlikedown onto planets, drawn by a planet's gravity, negative matter would shun planets It would be repelled, not attracted, by large bodies such as stars and planets Hence, although negative ht exist, we expect to find it only in deep space, certainly not on Earth

One proposal to find negativethe phenoht travels around a star or galaxy its path is bent by its gravity, according to general relativity In 1912 (even before Einstein fully developed general relativity) he predicted that a galaxy ht froe as it passed around the galaxy, like a lens, forht finally reached the Earth These phenos” In 1979 the first of these Einstein lenses was observed in outer space Since then, Einstein lenses have become an indispensable tool for astronoht that it would be impossible to locate ”dark matter” in outer space [Dark matter is a ht It surrounds the galaxies and is perhaps ten times as plentiful as ordinary visible matter in the universe] But NASA scientists have been able to construct ht passes through, in the saht) Therefore it should be possible to use Einstein lenses to search for negative ht in a peculiar hich should be visible with the Hubble space Telescope So far, Einstein lenses have not detected the iative matter or wor If one day the Hubble space Telescope detects the presence of negative matter or a wormhole via Einstein lenses, it could set off a shock wave in physics

Negative energy is different froative matter in that it actually exists, but only in minute quantities In 1933 Hendrik Casi the laws of the quantued parallel ic Normally parallel plates are stationary, since they lack any net charge But the vacuum between the two parallel plates is not empty, but full of ”virtual particles,” which dart in and out of existence

For brief periods of ti, only to be annihilated and disappear back into the vacuuht to be devoid of anything, now turns out to be churning with quantum activity Normally tiny bursts of matter and antiy But because of the uncertainty principle, these tiny violations are incredibly short-lived, and on average energy is still conserved

Casimir found that the cloud of virtual particles will create a net pressure in the vacuum The space between the two parallel plates is confined, and hence the pressure is low But the pressure outside the plates is unconfined and larger, and hence there will be a net pressure pushi+ng the plates together

Nory occurs when these two plates are at rest and sitting far apart froether, you can extract energy out of they has been taken out of the plates, the energy of the plates is less than zero

This negative energy was actually measured in the laboratory in 1948, and the results confiry and the Casier science fiction but established fact The problem, however, is that the Casimir effect is quite s equipeneral, the Casiy is proportional to the inverse fourth power of the distance of separation between the plates This er the energy) The Casimir effect was measured precisely in 1996 by Steven Lamoreaux at the Los Alamos National Laboratory, and the attractive force is 1/30,000 the weight of an ant

Since Alcubierre first proposed his theory, physicists have discovered a nue properties The people inside the starshi+p are causally disconnected from the outside world This means that you cannot siht You cannot co ”highway” through space and tiular timetable In this sense, the starshi+p would not be an ordinary shi+p that can change directions and speeds at will The starshi+p would actually be like a passenger car riding on a preexisting ”wave” of co corridor of warped space-tienerators of exotic hway, that manipulate space for you in a synchronized way”

Actually, even more bizarre types of solutions to Einstein's equations can be found Einstein's equations state that if you are given a certain a of space-tienerate (in the same way that if you throw a rock into a pond, you can calculate the ripples that it will create) But you can also run the equations backward You can start with a bizarre space-tiht Zone (In these universes, for example, you can open up a door and find yourself on the moon You can run around a tree and find yourself backward in tiht side of your body) Then you calculate the distribution of y associated with that particular space-tiiven a bizarre collection of waves on the surface of a pond, you can work backward and calculate the distribution of rocks necessary to produce these waves) This was, in fact, the way in which Alcubierre derived his equations He began with a space-tiht, and then he worked backward and calculated the energy necessary to produce it

WORMHOLES AND BLACK HOLES

Besides stretching space, the second possible way to break the light barrier is by ripping space, via woreways that connect two universes In fiction, the first mention of a worson, rote Through the Looking Glass under the pen na Glass of Alice is the worical world of Wonderland By placing her hand through the Looking Glass, Alice can be transported instantly from one universe to the next Mathematicians call these ”multiply connected spaces”

The concept of wormholes in physics dates back to 1916, one year after Einstein published his epic general theory of relativity Physicist Karl Schwarzschild, then serving in the Kaiser's army, was able to solve Einstein's equations exactly for the case of a single pointlike star Far froravitational field was very similar to that of an ordinary star, and in fact Einstein used Schwarzschild's solution to calculate the deflection of light around a star Schwarzschild's solution had an immediate and profound impact on astronomy, and even today it is one of the best-known solutions of Einstein's equations For generations, physicists used the gravitational field around this pointlike star as an approximation to the field around a real star, which has a finite diameter

But if you took this pointlike solution seriously, then lurking at the center of it was a monstrous pointlike object that has shocked and amazed physicists for almost a century-a black hole Schwarzschild's solution for the gravity of a pointlike star was like a Trojan Horse On the outside it looked like a gift from heaven, but on the inside there lurked all sorts of dehosts But if you accepted one, you had to accept the other Schwarzschild's solution showed that as you approached this pointlike star, bizarre things happened Surrounding the star was an invisible sphere (called the ”event horizon”) that was a point of no return Everything checked in, but nothing could check out, like a Roach Motel Once you passed through the event horizon, you never came back (Once inside the event horizon, you would have to travel faster than light to escape back outside the event horizon, and that would be impossible) As you approached the event horizon, your atoravity felt by your feet would be ravity felt by your head, so you would be ”spaghettified” and then ripped apart Similarly, the atoravity

To an outside observer watching you approach the event horizon, it would appear that you were slowing down in time In fact, as you hit the event horizon, it would appear that time had stopped!

Furtherht that has been trapped and circulating around this black hole for billions of years It would see the entire history of the black hole, going back to its very origin

And finally, if you could fall straight through to the black hole, there would be another universe on the other side This is called the Einstein-Rosen Bridge, first introduced by Einstein in 1935; it is now called a wormhole

Einstein and other physicists believed a star could never evolve naturally into such a monstrous object In fact, in 1939 Einstein published a paper showing that a circulating as and dust will never condense into such a black hole So although there was a wor in the center of a black hole, he was confident that such a strange object could never forton once said that there should ”be a law of nature to prevent a star fro in this absurd way” In other words, the black hole was indeed a legitimate solution of Einstein's equations, but there was no known mechanised with the advent of a paper by J Robert Oppenheimer and his student Hartland Snyder, written that sa that black holes can indeed be for star had used up its nuclear fuel and then collapsed under gravity, so that it iravity could co known to science could prevent gravity fro the star to a point-particle, the black hole (This iiven Oppenheiasaki bo a sphere of plutoniuh came in 1963, when New Zealand mathematician Roy Kerr examined perhaps the most realistic example of a black hole Objects spin faster as they shrink, inin their arms close to their body As a result black holes should be spinning at fantastic rates

Kerr found that a spinning black hole would not collapse into a pointlike star, as Schwarzschild assu Anyone unfortunate enough to hit the ring would perish; but so would not die, but would actually fall through But instead of winding up on the other side of the ring, he or she would pass through the Einstein-Rosen Bridge and wind up in another universe In other words, the spinning black hole is the ri Glass

If he or she were toa second time, he or she would enter yet another universe In fact, repeated entry into the spinning ring would put a person in different parallel universes,the ”up” button on an elevator In principle, there could be an infinite number of universes, each stacked on top of each other ”Pass through thisand-presto!-you're in a coative!” Kerr wrote

There is an important catch, however Black holes are exa through the event horizon is a one-way trip Once you pass through the event horizon and the Kerr ring, you cannot go backward through the ring and out through the event horizon

But in 1988 Kip Thorne and colleagues at Cal Tech found an exah which you could pass freely back and forth In fact, for one solution, the travel through a wor on an airplane

Norravity would crush the throat of the wor to reach the other side That is one reason that faster-than-light travel through a worative energy or negative mass could conceivably keep the throat open sufficiently long to allow astronauts a clear passage In other words, negative y is essential for both the Alcubierre drive and the wor number of exact solutions have been found to Einstein's equations that allow for wor wormholes

First, to create the violent distortions of space and tih a worative e star or a black hole Matthew Visser, a physicist at Washi+ngton University, estiy you would need to open up a 1-meter wormhole is comparable to the ative He says, ”You need abouta positive Jupiter y is already pretty freaky, well beyond our capabilities into the foreseeable future”

Kip Thorne of the California Institute of Technology speculates that ”it will turn out that the laws of physics do allow sufficient exotic matter in wormholes of human size to hold the wory for inably far beyond the capabilities of our human civilization”

Second, we do not kno stable these worenerated by these worht kill anyone who enters Or perhaps the wor as soon as one entered the into the black hole would be blue shi+fted; that is, they would attain greater and greater energy as they came close to the event horizon In fact, at the event horizon itself, light is technically infinitely blue shi+fted, so the radiation froy could kill anyone in a rocket

Let us discuss these probley to rip the fabric of space and time The simplest way to do this is to compress an object until it becomes smaller than its ”event horizon” For the sun, thisit down to about 2 miles in diameter, whereupon it will collapse into a black hole (The Sun's gravity is too weak to compress it naturally down to 2 miles, so our sun will never beco, even you, can become a black hole if you were sufficiently co all the atoms of your body to smaller than subatomic distances-a feat that is beyond the capabilities of modern science) A more practical approach would be to assemble a battery of laser beams to fire an intense beae atom smasher to create two beams, which would then collide with each other at fantastic energies, sufficient to create a small tear in the fabric of space-time

PLANCK ENERGY AND PARTICLE ACCELERATORS

One can calculate the energy necessary to create an instability in space and tiy, or 1019 billion electron volts This is truly an unier than the energy attainable with today's e Hadron Collider (LHC), located outside Geneva, Switzerland The LHC is capable of swinging protons in a large ”doughnut” until they reach energies of trillions of electron volts, energies not seen since the big bang But even this y anywhere near the Planck energy

The next particle accelerator after the LHC will be the International Linear Collider (ILC) Instead of bending the path of subatomic particles into a circle, the ILC will shoot they will be injected as the particles e energies Then a beae burst of energy The ILC will be 30 to 40 kiloth of the Stanford Linear Accelerator, currently the largest linear accelerator If all goes well, the ILC is due to be coy produced by the ILC will be 5 to 10 trillion electron volts-less than the 14 trillion electron volts of the LHC, but this is deceptive (In the LHC, the collisions between the protons take place between the constituent quarksthe quarks are less than 14 trillion electron volts That is why the ILC will produce collision energies larger than those of the LHC) Also, because the electron has no known constituent, the dynamics of the collisions between electron and antielectron are simpler and cleaner

But realistically, the ILC, too, falls far short of being able to open up a hole in space-time For that, you would need an accelerator a quadrillion times more powerful For our Type 0 civilization, which uses dead plants for fuel (eg, oil and coal), this technology is far beyond anything we can muster But it may become possible for a Type III civilization

Realactic in its use of energy, consuy than a Type II civilization, whose consule star And a Type II civilization in turn consuy than a Type I civilization, whose consule planet In one hundred to two hundred years, our feeble Type 0 civilization will reach Type I status

Given that projection, we are a long, long way froy Many physicists believe that at extremely tiny distances, at the Planck distance of 10-33 centimeters, space is not e with tiny bubbles that constantly pop into existence, collide with other bubbles, and then vanish back into the vacuum These bubbles that dart in and out of the vacuum are ”virtual universes,” very similar to the virtual particles of electrons and antielectrons that pop into existence and then disappear

Normally, this quantum space-time ”foam” is completely invisible to us These bubbles form at such tiny distances that we cannot observe theh energy at a single point, until we reach the Planck energy, these bubbles can beco with tiny bubbles, each bubble a wormhole connected to a ”baby universe”

In the past these baby universes were considered an intellectual curiosity, a strange consequence of purethat our universe inally started off as one of these baby universes

Such thinking is sheer speculation, but the laws of physics allow for the possibility of opening a hole in space by concentrating enough energy at a single point, until we access the space-ti our universe to a baby universe

Achieving a hole in space would, of course, require ht be possible for a Type III civilization For exa called a ”Wakefield tabletop accelerator” Remarkably, this atom smasher is so senerate billions of electron volts of energy The Wakefield tabletop accelerator works by firing lasers onto charged particles, which then ride on the energy of that laser Experiments done at the Stanford Linear Accelerator Center, the Rutherford Appleton Laboratory in England, and the ecole Polytechnique in Paris show that enor laser beah was ineers at the Stanford Linear Accelerator Center, UCLA, and USC dee particle accelerator in just 1 meter They started with a bea tube in Stanford, reaching an energy of 42 billion electron volts Then these high-energy electrons were sent through an ”afterburner,” which consisted of a plas, where the electrons pick up an additional 42 billion electron volts, doubling their energy (The plasas As the electrons pass through the gas, they create a plasma wave that creates a wake This wake in turn flows to the back of the electron bea it an extra boost) In this stunning achievement, the physicists improved by a factor of three thousand the previous record for the ay persuch ”afterburners” to existing accelerators, one y, almost for free

Today the world record for a Wakefield tabletop accelerator is 200 billion electron volts per er distances (such asthe stability of the bea that we could maintain a power level of 200 billion electron volts perthe Planck energy would have to be 10 light-years long This is ithin the capability of a Type III civilization

Worive us the ht barrier But it is not known if these technologies are stable; if they are, it would still take a fabulous aative, to make theht already have this technology Itpower on this scale Because there is still controversy over the funda the fabric of space-time at the quantum level, I would classify this as a Class II impossibility

12: TIME TRAVEL

If time travel is possible, then where are the tourists from the future?