Time travel


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Time travel

  1. 1. LET’S TALK ABOUT THE FUTURE! TIME TRAVEL - going backwards and forwards in time has always sparked people’s imaginations. by ”Nichita Stănescu” Highschool s eTwinning team Time travel is a concept that has lived in the human consciousness for thousands of years. But are such tales only possible in the realms of science fiction and fantasy? Almost all of us have seen one or two movies featuring time travel. The concept of going backwards and forwards in time has always sparked people’s imaginations. Historically, it has always been considered nothing more than only science fiction; however, this changed when Albert Einstein’s theory of relativity opened the door for the possibility of time travel. This gave us a new way to view space and time — one that was very different from the existing picture established by Isaac Newton. Newton’s classical mechanics was based on the premise that time passes uniformly anywhere and everywhere. Einstein’s special theory of relativity, however, tells us that the flow of time is not
  2. 2. constant everywhere in the universe. The faster you move, the slower time will be–until you reach the speed of light, where the flow of time will appear to stop. This essentially proves that time travel into the future is possible; all you need to do is ride a spaceship that moves at a speed close to the speed of light, orbit the Earth for quite some time, and then return. If your spaceship moves at 95% the speed of light and you orbited Earth for 1 year, when you return 10 years would have passed on Earth. This theory also tells us that if you move faster than the speed of light, you will be able to travel back in time. Of course, as most of us might already know, nothing can go faster than light, but Einstein’s other theory of general relativity has some predictions that may allow us to cheat the laws of physics and travel faster than light. Einstein’s general theory of relativity deals with gravity and the fabric of spacetime. In Einstein’s picture of the universe, space and time are combined into one spacetime, and the geometry of spacetime is affected by the matter that is in it. Einstein showed that the fabric of spacetime can be bent, stretched or twisted depending on the matter within it. We can take advantage of this to be able to travel faster than light; all
  3. 3. we need is a rotating black hole. The rotating black hole continuously twists the spacetime around it. Therefore, if we could orbit the black hole at a speed very close to the speed of light, an outside observer would see us moving at a speed faster than light depending on how fast the spacetime is being twisted. We are not breaking the laws of physics here, as we are not actually moving faster than light. It is when viewed from the outside that we will appear to be doing so, because of the addition of velocities. So, When Einstein first put together his theories, he concluded that space and time are one entity instead of two separate ones acting independently from the other. This is now called the space-time continuum. So, we also know that light travels at a speed that is almost perfectly constant across the vast expanse of mostly empty space. Since photons have no mass, they are able to travel at the universal speed limit, which measures out to be about 300,000 kilometers per second (or 186,000 miles per second). This is what we know as “the speed of light.” Literally, nothing (that we know of) can travel faster than this speed.
  4. 4. Hopefully you’ve heard of Einstein’s famous equation E = mc^2, which revealed one of the most profound, life-changing discoveries of all time. You may know of it as the mass/energy equivalence. Essentially, matter is equal to energy (they are different expressions of the same thing). When something speeds up, its energy will increase too since energy is equal to mass (and vice versa). The heavier the object is, the more energy that is required to make it accelerate. Therefore, you would eventually need more and more energy to make the object continue moving at light-speed. The most interesting portion of Einstein’s theory of special relativity probably has to be the implications of what happens to particles traveling near or at the speed of light. It says that time tends to go much slower for particles traveling at the speed of light than it would for an outside monitoring the photon’s progress from afar. Interestingly, this is one aspect of special relativity that can be tested here on Earth! Our satellites in LEO (lowEarth orbit) must take into account the effects of special relativity when calibrating their onboard clocks, which ticks with an accuracy of one nanosecond (about 1 billionth of a second).
  5. 5. As an example, GPS satellites are capable of determining your exact position on Earth with an accuracy of 5 to 10 meters, but to achieve that level of precision, the clocks on board must be accurate to 20-30 nanoseconds. Because an observer on the ground (in your car in this instance) sees the satellite in space in motion relative to them, the clocks onboard will tick more slowly than the one in your car, causing them to be off by about 7 microseconds per day due to the time dilation effect of the relative motion of the two. Assuming YOU were able to travel very close to the speed of light, you would experience time much more differently than someone observing your movement from Earth. Hypothetically, what you would experience as a second may feel like a minute to the observer, this is called time dilation. Theoretically, this could make you experience time backwards, which would violate causality (the chronological order of influence of things in the universe) not to mention how we perceive things from the floating rock we are chained to currently. You’re probably wondering how this would work, but the details are kind of fuzzy to us too since most of the laws of physics point to this being very unlikely (if not impossible). If it
  6. 6. were possible, as you approached light speed, the outside universe would begin to slow down in relation to you (or whatever else that’s traveling at the speed of light) before it stops. For you; that is. The observer will experience time the way they typically do. Once you exceed light speed, the outside world would slow down to the point that space/time would be moving backwards in relation to you. Again, there is little evidence to suggest that faster than light travel is possible to begin with and that’s just for subatomic particles, which don’t have the mass that we (humans) do. If it were, there would be some incredibly awesome implications in the world of physics. One hypothesis postulates that it could be possible to communicate with the past using neutrinos, which famously invaded the news for a few months in 2011; after physicists thought they had evidence that suggested neutrinos were traveling just a bit faster than light speed. As it turns out, there were issues with the equipment and they didn’t actually observe neutrinos traveling faster than the universal speed limit. Even if we could, it’s quite unlikely the message would even be received since they don’t interact much
  7. 7. with normal matter. It is kind of humbling to note that the past is very much a part of the universe as much as the present. Another prediction of general relativity that we can use is the Einstein-rosen bridge, or as it is more popularly known, a wormhole. A wormhole is a cosmic shortcut from one point in spacetime to another. It can be visualized by making two separate points on a piece of paper meet by folding the paper. We should remember that Einstein combined space and time into one so we can use a wormhole to travel through both space and time. It is still not certain how we can make a wormhole, and once we are able to make one general relativity tells us that it will only last for a very brief amount of time. Keeping the wormhole open will be another problem. The possibility of travelling back in time has long been debated. Most are convinced that it is impossible because of the many paradoxes it can cause, particularly on the law of causality. The law of causality states that the cause should always happen before its effect. This law can be broken by backwards time travel, as is shown by the famous grandfather paradox. If you will go back in time and kill your grandfather, your father, and hence you, will not be born.
  8. 8. If you were not born, you will not be able to kill your grandfather, hence, you will be born, and you will be able to kill your grandfather, and so on… Another paradox concerns the passage of information from one time to another. Let’s say that we go back in time and teach the young Isaac Newton all the laws of physics that he himself discovered. Now, where did those laws come from? We can no longer say that it came from Newton because we taught him those ideas. We, on the other hand, cannot say that it came from us, as obviously it came from Newton. Lastly, the easiest paradox to understand is why don’t we see time travellers from the future? There are many more paradoxes that we can think of with backwards time travel but fortunately, modern physics has a solution to these paradoxes. To resolve the paradox of going back in time, some physicists say that if you were to go back in time, you would arrive in the past of another universe. So, when you go back in time, you will arrive in another timeline, a timeline that you can be able to affect in every way without causing paradoxes. This theory of parallel universes arises from the probabilistic nature of quantum mechanics. In quantum mechanics, you cannot tell the specific
  9. 9. position of a particle, rather you can only compute for the possibility that it will be in a specific place. Every one of those possibility happens, not in our universe but in another universe. In fact, this theory tells us that there are an infinite number of parallel universes, one of which may have me inventing an iron man suit, or another in which you are Batman. According to some, time travel is slowly becoming a reality. If we are somehow able to travel through time, we could become masters of the universe (or very nearly so). The philosophical and scientific basis for time travel is still being debated upon, but once we do invent a time machine (and I’d like to think it is at least possible that we will), it will be the most important discovery of humankind. Source: http://en.wikipedia.org/wiki/Albert_Einstein http://en.wikipedia.org/wiki/The_Einstein_Theory_of_Relativity http://einstein.biz/