4 Time Travel Theories and the Physics Behind Them
Time travel has been the subject of many science-fiction books and films for the last few decades.
But is it possible? Are there any time travel theories that could actually work? We are all time travellers. That is to say, we all travel through time. We travel at the same time as each other; one hour per hour, and moving forward in a straight line, towards the future. But what if we could speed up or slow down time? What if we could visit the past? Take a sneak peek into the future? What if we could really time travel? Some think the concept of time travel is promising. Before we examine time travel theories, we should first visit Albert Einstein’s explanation of time.
The majority of people view time as a constant, linear construct. One that moves forward at a regular pace. After all, we organise our lives around a 24-hour clock, a 12-month calendar, and so on. However, Einstein showed that time can change, depending on your position in space. Space is the three dimensions we inhabit; length, width and height. We use these dimensions to pinpoint our location. Imagine you are walking to work.
The space you inhabit includes the length of the road, the width of a path and the height of buildings around you. But there is another dimension and that’s time. Time is the fourth dimension which shows our direction, which is always moving forward. Now, Einstein’s Theory of Special Relativity proposes that time does not pass at the same rate for everyone. It varies depending on your particular position through space. For example, whether you are an observer or travelling yourself. Time can speed up or slow down depending on how fast you are moving in relation to another object. Now we know that time does not remain the same for everyone, it is conceivable that there are plausible theories of time travel. In fact, all astronauts are time travelling as we speak. This is because you move faster in space through time than you do on earth. Which leads us onto the first theory of time travel: Experts have calculated the speed of light at 186,282 miles per second. This equates to 299,792 kilometres per second or an incredible 670,616,629 mph. In theory, there is nothing that travels faster than light. But if we turn to Einstein’s special theory again, we know that time is not a single construct for everyone. Time passes at different speeds depending on the observer, their motion and the speed. British Professor Brian Cox explains that the closer we get to the speed of light, the more time slows down. It’s all to do with how fast we go in relation to those who are standing still. Time slows down but only for the object that is moving. “If you go fast, your clock runs slow relative to people who are still. As you approach the speed of light, your clock runs so slow you could come back 10,000 years in the future.” Prof Brian Cox So how can we travel backwards or forwards in time? Using the ‘speed of light’ time travel theory, building a Faster-Than-Light (FTL) Machine is the way to go. It would have to be the fastest ever man-made spaceship as it would need to travel at over 670 million mph. As a reference, the fastest NASA has ever managed to produce is the Helios 2 space probe. This blasted off in 1976 and got up to 160,000 mph when in space. However, if we did manage to build a spacecraft capable of faster-than-light speeds, the consequences to time and our ages would be incredibly interesting. For instance, even if we didn’t manage to travel at the top speed of light, at 99%, every year spent on the FTL spacecraft would result in seven years back on earth. At 99.999%, this increases to one year on the spacecraft to 223 back on earth. In fact, some experts believe that we could reverse time if we actually manage to travel at the speed of light. Unfortunately, Einstein states that anything with a mass cannot physically reach the speed of light, let alone pass it. Still, if we can’t travel faster than the speed of light, are there other theories that don’t involve speed but suggest time travel is plausible? How often have we heard Captain Kirk or Picard instructing their engineers to set engines to warp drive on Star Trek? But as so many sci-fi programmes start off, so do scientists take over. Experts are now saying that warp drive could be possible, and it’s all to do with stretching the fabric of space-time. Imagine space is a large piece of material. On the material are the planets, stars, constellations, galaxies etc. One way to time travel would be to move space around the object travelling. This is the Alcubierre Drive. Our spaceship pushes up the fabric of space in front of the ship. This causes the fabric to contract at the front and expand at the back.
The ship rides this bubble of space-time which is constantly contracting and expanding. But it’s not violating the laws of physics as it is not travelling faster than light. As with all of our time travel theories, there are some problems, and these are pretty big ones at that. Early estimates of the energy required to power a spaceship just 200m wide came out at billions x the mass of the observable universe. Now scientists have refined this estimate to the equivalent mass of Jupiter, but it’s still woefully unachievable. We also don’t know how to stop the bubble once we arrive at our destination. Speaking about the fabric of the universe, perhaps the way the universe formed can assist our quest for time travel? Astrophysicist at Princeton University J. Richard Gott certainly thinks so. In 1991, he proposed the idea of Cosmic Strings.
These strings are present throughout the universe.
They resemble string-like phenomenon and are described as ‘cracks in the universe’. Gott explains them as: “Cosmic strings are either infinite or they’re in loops, with no ends. So they are either like spaghetti or Spaghetti Os.” J. Richard Gott Cosmic strings are everywhere in the universe.
They are similar to black holes in that they’re under tremendous pressure. This means they have a significant gravitational pull, and warp the space around them, just like black holes. But whereas black holes crush everything they pull inside, cosmic strings could enable an object to attach onto it and fly through space at amazing speeds. “The approach of two such strings parallel to each other, will bend space-time so vigorously and in such a particular configuration that might make time travel possible – in theory,” Gott interviewed for Live Science. Even so, this is just one of many theories of time travel. Because as yet, no cosmic strings have ever been discovered. All of these theories show that time travel is either outlandishly impossible, not proven or will require unheard amounts of energy. So should we still be pursuing time travel? Or, with the recent climate change problems on earth, perhaps our resources would be better spent here on this planet? I’ll leave the last word to Joseph Agnew – an undergraduate engineer and research assistant from the University of Alabama (PRC). He’s currently working on the theory of time travel via warp drive: “In terms of justifications for allocation of resources, it is not hard to see that the ability to explore beyond our Solar System, even beyond our Galaxy, would be an enormous leap for mankind. And the growth in technology resulting from pushing the bounds of research would certainly be beneficial.” Joseph Agnew R.
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