Is time travel possible? People who say that that it is not should think again. After all, weāre all time travelers, scooting along through the space-time continuum at a rate of one second per second. It’s also fun to imagine traveling at near-light speeds to investigate the future, something that is already an established scientific fact. However, it’s generally accepted that time travel is a one-way trip, only going forward, and while there may be some truth to the assumption, it’s certainly not guaranteed.
Of course, traveling back in time also appears to throw up a number of time travel paradoxes that might seem difficult to resolve. These include the Bootstrap Paradox, the Predestination Paradox, and the Grandfather Paradox.
Nevertheless, Einstein’s equations do not rule out the possibility of backward time travel. Consequently, scientists and science fiction writers alike have devoted serious time and effort investigating this absorbing subject.
Time Travel Methods
There are many theoretical methods of time travel that might make traveling to the future or past a possibility. Let’s delve further into some of the fascinating methods of time travel that scientists have devised.
TravelĀ Very Fast
Einstein showed time is flexible and can be affected by speed, with his Theory of Relativity showing that as you approach the speed of light (186,282 miles per second) time slows down. Astronauts on board the International Space Station traveling at 17,000 miles per hour, for instance,Ā age 0.014 seconds less than earthbound humans every year. Relativistic time travel even rears its head for the constellation of GPS satellites. If it wasnāt for automatic corrections built into the system, geolocation would be inaccurate by as much as 6 miles (10 km) a day.
Build an FTL Machine
Going very fast will help you travel marginally into the future, but building a machine that travels faster-than-light (FTL) will take your time-traveling odyssey to a whole new level. Of course, there’s the slight problem that the fastest ever human-made object, NASA’s Helios 2 space probe launched in 1976 attained a speed of 160,000 mph in space. This, obviously, is a far cry from the 671 million mph that light travels.
Still, if traveling at 99% of the speed of light was possible you would experience 1 year on board your FTL craft for roughly every 7 back on Earth. At 99.999% of the speed of light, that figure would subsequently rise to 1 year for every 223 years back on Earth. Some have speculated that exceeding the speed of light might actually cause time to reverse. Of course, there’s the problem that when you attain 99.999 the speed of light as your mass becomes infinite making it impossible to accelerate any further.
Look Back in Time
FTL travel could also present us with the intriguing theoretical possibility of traveling four light-hours away from Earth, turning around, and watching the light from Earth 4 hours ago arrive. We would essentially be watching 4 hours of history from Earth being replayed as its light arrived. Even now, thereās nothing to preclude us looking back through time to observe events from long ago. Every time you gaze out at the stars youāre looking at history; youāre looking at things that occurred thousands or hundreds of thousands of years ago.
With a good telescope, you can watch things that happened millions of years ago. If you just want to look into the past 4.24 years you can look at the closest star (after the Sun) to the planet Earth. Itās part of a triple star system, and its name is Proxima Centauri. The next separate star system has a sun named Barnardās Star which is 9 Ā½ light years away. So by focusing our attention on either of these two systems you can look 4 Ā¼ years into the past or 9 Ā½ years into the past, respectively.
Warp Drive
Warp Drive, as described by theoretical physicist Miguel Alcubierre, involves moving a bubble of space-time through a relativistic framework. Unfortunately for time travel enthusiasts you are now moving in a non-relativistic way, and you may have two separate time frames, but theyāre both running at the same rate. If it takes an hour to get to Pluto, an hour of time passes back on Earth. In other words, you may have traveled vast distances through space, but your time has still remained the same.
Wormholes
A wormhole is a hypothetical passage in space-time connecting two separate points, thus giving the traveler the chance to traverse potentially astronomical distances instantaneously. Furthermore, general relativity predicts that if traversable wormholes do spontaneously exist, they could permit time travel through relativistic time dilation.
However, there is no way to predict where the other end of them would be. Worse yet, theories seem to indicate it would be a one-use sort of thing, collapsing behind you as you pass through it. If it went anywhere, that would be the end of the journey ā there would be no hope of return, and no way for someone to follow. We donāt currently possess or understand a method for generating a wormhole, but current estimates suggest that we would need the output of an entire sun to create one. With only one Sun in our solar system, which happens to be in use at the moment, I suggest this is not very practical, completely aside from the fact that we donāt know how to harness it.
Black Holes
Einstein discovered that gravity from massive object cause time to slow down. Therefore, while black holes will simply crush anything that enters them, by staying outside of its event horizon you could travel years into the future relative to an observer beyond its gravitational field, while for you just a few days would have elapsed.
Neutron Stars
Neutron stars spin very quickly. The fastest one found in our galaxy rotates at 716 times per second, which is approaching 25% of the speed of light. If a spinning neutron star were to collapse to a black hole the centrifugal effect might very well cause it to form a ring of protons that do not collapse to a singularity.
This āspinning doughnutā might not stretch you out into an infinitely long piece of spaghetti, but rather cause a rupture in the space-time continuum at the nexus of that doughnut. The other end might spontaneously form at another weak point elsewhere in the galaxy. There are a number of readily apparent possibilities – you are ripped to shreds; you get stuck forever; you end up outside our galaxy; you exit in the future; or you exit in the past. Another possibility is that you exit in a parallel universe. If it so happens to be one where our laws of physics donāt apply, then you would simply cease to exist as your atoms will no longer obey the laws of your own universe.
Superstrings
If superstrings exist, one with the diameter of a proton and 1.6 km long would weigh as much as the entire planet Earth. If you can arrange to have two of these side by side and start orbiting the two strings in a figure-eight pattern, through some very esoteric and complex mathematical operations this would allow you to travel forward or backward in time, to transmit matter from point to point, or travel to any point that you could calculate.
The funny thing is that the strings would have minimal gravity despite their mass as long as they were straight. If they were formed into loops, however, they would possess the full gravity of our planet. No matter how intimidating the mathematics, thereās still no evidence that superstrings exist, though. They still remain a theoretical construct to explain some phenomena that we donāt completely understand yet.
Different Dimensions
We can add a whole new dimension to the discussion; seven of them in fact! Quantum theory currently requires 10 dimensions, or 11 if you include time, in order to describe itself. But where are they? You can see lengths, you can see widths, you can see heights; they are perfectly obvious. The fourth dimension is duration or time. So where are the seven other dimensions? Picture these dimensions as flower petals that havenāt unfurled. Theyāre tightly held at the corners of all the other dimensions. If there was another direction you could travel other than up, down, left, right, forward, or back, it would be quantified by one of these dimensions.
Robert A. Heinlein, both a scientist and a science fiction writer, wrote a book titled Number of the Beast. In his novel, one of the protagonists created a device where he could swap one dimension for another. People in the book would continue to perceive three dimensions, but if you traveled along this new dimension that might have taken the place of ālengthā you could travel into the future, or into the past. Other dimensional swaps would allow you to transit to parallel universes, while another would allow you to transit to a different physical location in the blink of an eye.
Maybe he was on to something. Maybe it is as simple as swapping one dimension for another. Weāre basically three-dimensional creatures. We can handle length, width, and depth. Maybe by rotating out one dimension and rotating in another we can accomplish anything. The secret is to let quantum physicists figure out how to make it actually work. It might only require knowledge and a very tiny expenditure of energy. You could step into a āboothā in your home, twist a knob, and step out of the booth, halfway around the world, in a fancy restaurant, or in a lunar base on the far side of the Moon, ready for a nightās observation. Think it unlikely? At this point, it makes sense to refer to one more of Arthur C. Clarkeās laws.
Clarkeās Third Law: Any sufficiently advanced technology is indistinguishable from magic.