Einstein's Theory of Special Relativity
The idea of relativistic time is a direct result of Albert Einstein's Theory of Relativity Space-time as a whole can therefore be thought of as a collection of an infinite . (close to the speed of light) with respect to one another, such intuitive relationships from the outside to stop completely due to the infinite time dilation effect. That is why we do not feel, do not understand that the space-time continuum is . relation of space, time matter and motion, which is very close to that of Hegel. .. knows what space and time is in their everyday life: no infinity in nature at all!. Traveling through time — possible in theory — is beyond our current an object at the speed of light would have both infinite mass and a length of 0. or otherwise interferes in their relationship — think "Back to the Future".
Now the train starts to move in the direction of the balland you again measure the speed of the ball. You would rightly calculate it as higher — the initial speed ie, when the train was at rest plus the forward speed of the train.
On the train, meanwhile, the game-player will notice nothing different. Your two values for the speed of the ball will be different; both correct for your frames of reference.
Replace the ball with light and this calculation goes awry. If the person on the train were shining a light at the opposite wall and measured the speed of the particles of light photonsyou and the passenger would both find that the photons had the same speed at all times.The Geometry of Causality - Space Time
In all cases, the speed of the photons would stay at just underkilometres per second, as Maxwell's equations say they should. Einstein took this idea — the invariance of the speed of light — as one of his two postulates for the special theory of relativity. The other postulate was that the laws of physics are the same wherever you are, whether on an plane or standing on a country road. But to keep the speed of light constant at all times and for all observers, in special relativity, space and time become stretchy and variable.
Time is not absolute, for example. A moving clock ticks more slowly than a stationary one. Travel at the speed of light and, theoretically, the clock would stop altogether. How much the time dilates can be calculated by the two equations above. In our example above, this would be the person in the train.
This led to further musings on light's behavior — and its incongruence with classical mechanics — by Austrian physicist Ernst Mach and French mathematician Henri Poincare. Einstein began thinking of light's behavior when he was just 16 years old, in He did a thought experiment, the encyclopedia said, where he rode on one light wave and looked at another light wave moving parallel to him.
Classical physics should say that the light wave Einstein was looking at would have a relative speed of zero, but this contradicted Maxwell's equations that showed light always has the same speed: Another problem with relative speeds is they would show that the laws of electromagnetism change depending on your vantage point, which contradicted classical physics as well which said the laws of physics were the same for everyone.
This led to Einstein's eventual musings on the theory of special relativity, which he broke down into the everyday example of a person standing beside a moving train, comparing observations with a person inside the train. He imagined the train being at a point in the track equally between two trees. If a bolt of lightning hit both trees at the same time, due to the motion of the train, the person on the train would see the bolt hit one tree before the other tree.
But the person beside the track would see simultaneous strikes. Learn the basics of Einstein's theory of relativity in our infographic here.
Why you can't travel at the speed of light | Science | The Guardian
By Karl Tate, Infographics Artist One of the most famous equations in mathematics comes from special relativity. If mass is somehow totally converted into energy, it also shows how much energy would reside inside that mass: This equation is one of the demonstrations for why an atomic bomb is so powerful, once its mass is converted to an explosion.
This equation also shows that mass increases with speed, which effectively puts a speed limit on how fast things can move in the universe. Simply put, the speed of light c is the fastest velocity at which an object can travel in a vacuum. As an object moves, its mass also increases.
Near the speed of light, the mass is so high that it reaches infinity, and would require infinite energy to move it, thus capping how fast an object can move. The only reason light moves at the speed it does is because photons, the quantum particles that make up light, have a mass of zero.
- Einstein's Theory of Special Relativity
- Why you can't travel at the speed of light
- Does light experience time?
A special situation in the universe of the small, called "quantum entanglement," is confusing because it seems to involve quantum particles interacting with each other at speeds faster than the speed of light. They wouldn't know about the flat three-dimensional space, in which the surface of the Earth lives.
For them, space would be curved, and geometry would be non-Euclidean. It would be very difficult to design a living being that could exist in only two dimensions. Food that the creature couldn't digest would have to be spat out the same way it came in. If there were a passage right the way through, like we have, the poor animal would fall apart.
So three dimensions, seems to be the minimum for life. But just as one can think of two dimensional beings living on the surface of the Earth, so one could imagine that the three dimensional space in which we live, was the surface of a sphere, in another dimension that we don't see. If the sphere were very large, space would be nearly flat, and Euclidean geometry would be a very good approximation over small distances.
But we would notice that Euclidean geometry broke down, over large distances. As an illustration of this, imagine a team of painters, adding paint to the surface of a large ball. As the thickness of the paint layer increased, the surface area would go up.
If the ball were in a flat three-dimensional space, one could go on adding paint indefinitely, and the ball would get bigger and bigger. However, if the three-dimensional space, were really the surface of a sphere in another dimension, its volume would be large but finite. As one added more layers of paint, the ball would eventually fill half the space. After that, the painters would find that they were trapped in a region of ever decreasing size, and almost the whole of space, was occupied by the ball, and its layers of paint.
So they would know that they were living in a curved space, and not a flat one. This example shows that one can not deduce the geometry of the world from first principles, as the ancient Greeks thought. Instead, one has to measure the space we live in, and find out its geometry by experiment.
However, although a way to describe curved spaces, was developed by the German, George Friedrich Riemann, init remained just a piece of mathematics for sixty years. It could describe curved spaces that existed in the abstract, but there seemed no reason why the physical space we lived in, should be curved. This came only inwhen Einstein put forward the General Theory of Relativity. General Relativity was a major intellectual revolution that has transformed the way we think about the universe.
It is a theory not only of curved space, but of curved or warped time as well. Einstein had realized inthat space and time, are intimately connected with each other. One can describe the location of an event by four numbers. Three numbers describe the position of the event.
They could be miles north and east of Oxford circus, and height above sea level. On a larger scale, they could be galactic latitude and longitude, and distance from the center of the galaxy. The fourth number, is the time of the event. Thus one can think of space and time together, as a four-dimensional entity, called space-time. Each point of space-time is labeled by four numbers, that specify its position in space, and in time.
Combining space and time into space-time in this way would be rather trivial, if one could disentangle them in a unique way. That is to say, if there was a unique way of defining the time and position of each event.
However, in a remarkable paper written inwhen he was a clerk in the Swiss patent office, Einstein showed that the time and position at which one thought an event occurred, depended on how one was moving. This meant that time and space, were inextricably bound up with each other. The times that different observers would assign to events would agree if the observers were not moving relative to each other. But they would disagree more, the faster their relative speed.
So one can ask, how fast does one need to go, in order that the time for one observer, should go backwards relative to the time of another observer.
Relativistic Time – Exactly What Is Time?
The answer is given in the following Limerick. There was a young lady of Wight, Who traveled much faster than light, She departed one day, In a relative way, And arrived on the previous night. So all we need for time travel, is a space ship that will go faster than light. Unfortunately, in the same paper, Einstein showed that the rocket power needed to accelerate a space ship, got greater and greater, the nearer it got to the speed of light. So it would take an infinite amount of power, to accelerate past the speed of light.
Einstein's paper of seemed to rule out time travel into the past. It also indicated that space travel to other stars, was going to be a very slow and tedious business.
If one couldn't go faster than light, the round trip to the nearest star, would take at least eight years, and to the center of the galaxy, at least eighty thousand years.
If the space ship went very near the speed of light, it might seem to the people on board, that the trip to the galactic center had taken only a few years.
But that wouldn't be much consolation, if everyone you had known was dead and forgotten thousands of years ago, when you got back. That wouldn't be much good for space Westerns. So writers of science fiction, had to look for ways to get round this difficulty.
In his paper, Einstein showed that the effects of gravity could be described, by supposing that space-time was warped or distorted, by the matter and energy in it.
We can actually observe this warping of space-time, produced by the mass of the Sun, in the slight bending of light or radio waves, passing close to the Sun.
This causes the apparent position of the star or radio source, to shift slightly, when the Sun is between the Earth and the source. The shift is very small, about a thousandth of a degree, equivalent to a movement of an inch, at a distance of a mile.
Nevertheless, it can be measured with great accuracy, and it agrees with the predictions of General Relativity. We have experimental evidence, that space and time are warped.
The amount of warping in our neighbourhood, is very small, because all the gravitational fields in the solar system, are weak. However, we know that very strong fields can occur, for example in the Big Bang, or in black holes. So, can space and time be warped enough, to meet the demands from science fiction, for things like hyper space drives, wormholes, or time travel.
At first sight, all these seem possible. For example, inKurt Goedel found a solution of the field equations of General Relativity, which represents a universe in which all the matter was rotating.
In this universe, it would be possible to go off in a space ship, and come back before you set out. Goedel was at the Institute of Advanced Study, in Princeton, where Einstein also spent his last years.
He was more famous for proving you couldn't prove everything that is true, even in such an apparently simple subject as arithmetic. But what he proved about General Relativity allowing time travel really upset Einstein, who had thought it wouldn't be possible. We now know that Goedel's solution couldn't represent the universe in which we live, because it was not expanding. It also had a fairly large value for a quantity called the cosmological constant, which is generally believed to be zero.
However, other apparently more reasonable solutions that allow time travel, have since been found. A particularly interesting one contains two cosmic strings, moving past each other at a speed very near to, but slightly less than, the speed of light. Cosmic strings are a remarkable idea of theoretical physics, which science fiction writers don't really seem to have caught on to.
As their name suggests, they are like string, in that they have length, but a tiny cross section. Actually, they are more like rubber bands, because they are under enormous tension, something like a hundred billion billion billion tons. A cosmic string attached to the Sun would accelerate it naught to sixty, in a thirtieth of a second.