Is time travel possible? “Maybe someone will come back from the future and tell us the answers.” — Stephen Hawking from the Preface, Black Holes and Time Warps: Einstein’s Outrageous Legacy, by Kip S. Thorne.
“One reason that time travel is so fascinating is that we have such a great desire to do it.” — J. Richard Gott, in his book, Time Travel in Einstein’s Universe: The Physical Possibilities of Travel Through Time.
Also from J. Richard Gott, “Einstein proved we can travel forward by moving near light speed. Backward requires a wormhole, cosmic string and a lot of luck.”
Scientists believe they may one day be able to travel through time by looking more closely at the dust swirling with a comet as it hurdles through our galaxy. — Goddard Space Flight Center
Accordingly, whether its Einstein, Hawkings, Gott, Thorne or a host of other top scientific minds, the word is that nothing in Newtonian physics, Einstein’s Theory of Relativity, or the laws of quantum mechanics is sufficient to prove time travel is impossible.
Currently, we can travel through the three dimensions of space pretty much at will moving forward or back, left or right, up or down. But when it comes to the 4th dimension of time were stuck.
The speculations that follow are purposefully random and non-linear. This is designed to promote the argument between linear and non-linear views of time and space where things occur either all at once or time marches on in one direction towards the future.
The possibility of time travel lies somewhere between phenomenon at cosmological scales and those at the quantum, subatomic level, while still conforming to the classical mechanics of motion, electromagnetism and relativity. Or, maybe it doesn’t. Traveling faster than the speed of light? Warping the time-space continuum? Parallel space-time continuums? Quarks, quasars, gamma ray bursts, positrons, black holes and wormholes? Is the universe expanding, contracting, infinite, warped? Inertia? Dark matter?
Some physicists allegedly have demonstrated that time travel is already taking place at the subatomic level, based on such theories at Time Reversal Invariance, String Theory, time dilation experiments and other theories.
It was in 1905 that Einstein introduced the Theory of Special Relativity, dramatically changing our understanding of time, space, and motion. Interestingly, H.G. Wells published his novel, The Time Machine, only 10 years before.
Special Relativity is based on two ideas. The first idea is that the laws of physics are the same for everyone as long as they are moving at a constant velocity. Einstein showed back in 1905 with his special theory of relativity that time slows down for objects moving close to the speed of light, that is, from the viewpoint of a stationary observer.
The second idea is that the speed of light is constant for everyone, whether its measured on earth or in a spaceship traveling at high speeds. In 1915 Einstein published his Theory of General Relativity, which permitted calculations based on changing speed.
The Theory of Special Relativity has undergone rigorous testing since Einstein first introduced it, so much so, that its no longer viewed as a theory.
Physics experiments, particularly in particle accelerators, continue to explore such areas as time dilation and time reversal invariance. Einstein concluded it would be impossible for a spaceship to reach the speed of light. However, scientists have used particle accelerators to make an electron attain 0.999 999 999 95% of light speed. Experiments continue to explore changing mass size of particles as they approach the speed of light. As mass size increases, the energy required to move mass also increases.
Physicists at the CPLEAR experiment have measured directly for the first time that, for the particles called kaons, time is different when it moves forwards or backwards. An international team is working on the experiment known as CPLEAR, at CERN, the European Laboratory for Particle Physics, in Geneva.
If fundamental particles can no longer be broken down into smaller particles, have we reached the end or the beginning, to be more exact? Does wave theory allow for more theoretical possibilities? Whats the difference between particles and waves and what bearing does such a difference have on time travel?
Some theories particularly of the unified field theory variety predict that the speed of light can change in time. Other theories predict particles can travel faster than the speed of light.
A positron (the antiparticle associated with the electron) can be considered to be an electron going backward in time. In an electron-positron pair where the positron is annihilated in a collision with another, different electron, a zigzag, N-shaped path takes shape: forward in time as an electron, then backward in time as a positron, then forward in time again as an electron.
The search for gravitons the particles of gravity holds promise in understanding the effects of gravity on time. Can time affect gravity? Is there a particle of time?
There seems to be a number of forces and/or factors that can warp time and space, from electromagnetism to black holes, from the shape of the universe to subatomic collisions at high energies, from crystalline forms of radiation to cosmic rays, from gravity to mass to velocity.
Some theorists claim travel into the past is not possible while others claim there are places where time doesn’t exist. Philosophizing about such theories is mind boggling enough yet alone fooling around with the mathematical equations that will ultimately prove or disprove one theory over another.
If time travel were possible, then where are the time travelers from the future? The latter question is similar to Fermis Paradox, which explores the notion that extraterrestrial life exists, but if so, then where are these so-called aliens?
Other influences on the possibility of time travel include chaos theory, quantum theory, string theory, M-Theory, theory of relativity, electromagnetic theory, gravity, space-time and even parallel universes.
How many worlds are there in the Many-Worlds theory?
Is what we imagine possible?
What does The Arrow of Time mean? Does time only travel one way into the future?
According to one interpretation of quantum theory (and there are many), each parallel world in a Parallel Universes theory is just as real as our own, with an alternative history for every possible outcome of every decision ever made.
The granny paradox or grandfather paradox, whichever gender frame of reference you choose, asks the question, what would happen if you went back into time and killed your grandmother, who gave birth to your mother, who gave birth to you? The rule seems to be you cant travel back or forward in the same universe you can’t undo what’s already been done. In turn, this means you cant undo what is going to be done, which means the future already exists.
By a process called “quantum tunneling,” one electron can disappear in one universe and appear in another. Can the same thing happen for things larger than an electron? What about the electrons in our own bodies? Does such tunneling occur externally or internally, such as in altered states of mind? If ghosts exist, then in what dimension do they exist? Is the body a time machine?
Wormholes seem to offer many possibilities for time travel. A wormhole is a thin tube of space-time connecting distant regions of the universe. Wormholes might also link to parallel or baby universes, providing the possibility of time travel. Wormholes are related to black holes, an effect allegedly created by sources of intense gravity where the fabric of space itself is bent, folded or distorted in various ways creating a short path between otherwise remote areas of space.
The wormhole was a fictional device used by Carl Sagan in his novel, Contact (1985). Kip S. Thorne and others at the California Institute of Technology set out to find whether wormholes were consistent with known physics. They speculated that a wormhole would resemble a black hole an object in space with tremendous gravity. Black holes are considered one-way journeys to nowhere. A wormhole has an exit and an entrance. Other scientists suggest a wormhole is a connection between two black holes.
And then theres anti-gravity.
Some scientists speculate a way to travel a 1000 years into the future is to travel to a star 500 light-years away and return, going both ways at 99.995% the speed of light. When returning, the earth will be 1,000 years older but the traveler will have aged only 10 years. Likewise, if an astronaut was sent to the planet Mercury and lived there for 30 years before returning, the astronaut would be about 22 seconds younger than if the astronaut had stayed on earth.
Clocks on Mercury tick more slowly than those on Earth because Mercury circles the sun at a faster speed. Gravity allegedly affects clocks much like velocity does and Mercury falls into a different gravitational field in relation to the sun than the earth does.
Cosmic strings, thin strands of energy millions of light-years long, offer other possibilities in terms of time travel.
Somewhere between quantum and chaos
Are schizophrenics receiving information from other worlds or perhaps time travelers? Could the voices prophets hear in their heads be the voices of time travelers?
What would happen if suddenly all our clocks stopped? Time wouldn’t stop, since time is a natural phenomenon. But clocks are man-made and subject to the forces of nature, like gravity, electromagnetism, space-time curvatures and other natural and cosmological forces. If clocks did stop, the world as we know it would be plunged into chaos.
Who knows, maybe time travel is a simple as a walk in the park. All it takes is a savvy 5th grader with a toy particle accelerator capable of producing wormholes.