Interesting Facts About Time, The Fourth Dimension, And Time Travel -
A four-dimensional space or 4D space is a mathematical extension of the concept of a paper consolidating the role of time as the fourth dimension of spacetime, the basis for Einstein's theories of Minkowski's geometry of space- time is not Euclidean, and consequently has no connection with the present investigation. "The problem of spooky action at a distance" is we look to the problem from our space time which is only real space time. The relation between elementary. “Minkowski space is not 3D + T, it is 4D,” the scientists write in their most recent paper. The concept of time as the fourth dimension of space - as a fundamental physical .. This a purely a function of mind in relation to reality.
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.
Physicists continue work to abolish time as fourth dimension of space
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.
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.Time Dilation - Einstein's Theory Of Relativity Explained!
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. Cosmic strings may sound far-fetched, and pure science fiction, but there are good scientific reasons to believed they could have formed in the very early universe, shortly after the Big Bang.
Because they are under such great tension, one might have expected them to accelerate to almost the speed of light. What both the Goedel universe, and the fast moving cosmic string space-time have in common, is that they start out so distorted and curved, that travel into the past, was always possible. God might have created such a warped universe, but we have no reason to think that He did. All the evidence is, that the universe started out in the Big Bang, without the kind of warping needed, to allow travel into the past.
Since we can't change the way the universe began, the question of whether time travel is possible, is one of whether we can subsequently make space-time so warped, that one can go back to the past. I think this is an important subject for research, but one has to be careful not to be labeled a crank.
If one made a research grant application to work on time travel, it would be dismissed immediately. No government agency could afford to be seen to be spending public money, on anything as way out as time travel. Instead, one has to use technical terms, like closed time like curves, which are code for time travel. Although this lecture is partly about time travel, I felt I had to give it the scientifically more respectable title, Space and Time warps. Yet, it is a very serious question.
Since General Relativity can permit time travel, does it allow it in our universe? And if not, why not. Closely related to time travel, is the ability to travel rapidly from one position in space, to another. As I said earlier, Einstein showed that it would take an infinite amount of rocket power, to accelerate a space ship to beyond the speed of light.
So the only way to get from one side of the galaxy to the other, in a reasonable time, would seem to be if we could warp space-time so much, that we created a little tube or wormhole.
This could connect the two sides of the galaxy, and act as a short cut, to get from one to the other and back while your friends were still alive.
Such wormholes have been seriously suggested, as being within the capabilities of a future civilization. But if you can travel from one side of the galaxy, to the other, in a week or two, you could go back through another wormhole, and arrive back before you set out.
You could even manage to travel back in time with a single wormhole, if its two ends were moving relative to each other. One can show that to create a wormhole, one needs to warp space-time in the opposite way, to that in which normal matter warps it. Ordinary matter curves space-time back on itself, like the surface of the Earth.
However, to create a wormhole, one needs matter that warps space-time in the opposite way, like the surface of a saddle. The same is true of any other way of warping space-time to allow travel to the past, if the universe didn't begin so warped, that it allowed time travel.
What one would need, would be matter with negative mass, and negative energy density, to make space-time warp in the way required. Energy is rather like money. If you have a positive bank balance, you can distribute it in various ways. But according to the classical laws that were believed until quite recently, you weren't allowed to have an energy overdraft. So these classical laws would have ruled out us being able to warp the universe, in the way required to allow time travel.
However, the classical laws were overthrown by Quantum Theory, which is the other great revolution in our picture of the universe, apart from General Relativity.
Quantum Theory is more relaxed, and allows you to have an overdraft on one or two accounts. If only the banks were as accommodating.
Space and Time Warps - Stephen Hawking
In other words, Quantum Theory allows the energy density to be negative in some places, provided it is positive in others. The reason Quantum Theory can allow the energy density to be negative, is that it is based on the Uncertainty Principle.
This says that certain quantities, like the position and speed of a particle, can't both have well defined values. The more accurately the position of a particle is defined, the greater is the uncertainty in its speed, and vice versa. The uncertainty principle also applies to fields, like the electro-magnetic field, or the gravitational field.
It implies that these fields can't be exactly zeroed, even in what we think of as empty space. For if they were exactly zero, their values would have both a well-defined position at zero, and a well-defined speed, which was also zero. This would be a violation of the uncertainty principle. Instead, the fields would have to have a certain minimum amount of fluctuations.
One can interpret these so called vacuum fluctuations, as pairs of particles and anti particles, that suddenly appear together, move apart, and then come back together again, and annihilate each other.
These particle anti particle pairs, are said to be virtual, because one can not measure them directly with a particle detector. However, one can observe their effects indirectly. One way of doing this, is by what is called the Casimir effect. One has two parallel metal plates, a short distance apart. The plates act like mirrors for the virtual particles and anti particles.
This means that the region between the plates, is a bit like an organ pipe, and will only admit light waves of certain resonant frequencies. The result is that there are slightly fewer vacuum fluctuations, or virtual particles, between the plates, than outside them, where vacuum fluctuations can have any wavelength. The reduction in the number of virtual particles between the plates means that they don't hit the plates so often, and thus don't exert as much pressure on the plates, as the virtual particles outside.
There is thus a slight force pushing the plates together. This force has been measured experimentally. So virtual particles actually exist, and produce real effects. Because there are fewer virtual particles, or vacuum fluctuations, between the plates, they have a lower energy density, than in the region outside.
But the energy density of empty space far away from the plates, must be zero. Otherwise it would warp space-time, and the universe wouldn't be nearly flat. So the energy density in the region between the plates, must be negative. We thus have experimental evidence from the bending of light, that space-time is curved, and confirmation from the Casimir effect, that we can warp it in the negative direction.
Each clock's ticking mechanism consists of a photon being reflected back and forth between two mirrors, so that a photon's path from one mirror to the other represents one tick of the clock. The clocks are arranged perpendicular to each other on a platform, with clock A oriented horizontally and clock B vertically.
When the platform is moved horizontally at a high speed, then according to the length contraction phenomenon in 4D spacetime, clock A should shrink so that its photon has a shorter path to travel, causing it to tick faster than clock B.
But Sorli and Fiscaletti argue that the length contraction of clock A and subsequent difference in the ticking rates of clocks A and B do not agree with special relativity, which postulates that the speed of light is constant in all inertial reference frames. They say that, keeping the photon speed the same for both clocks, both clocks should tick at the same rate with no length contraction for clock A.
They mathematically demonstrate how to resolve the problem in this way by replacing Minkowski 4D spacetime with a 3D space involving Galilean transformations for three spatial coordinates X, Y, and Z, and a mathematical equation Selleri's formalism for the transformation of the velocity of material change, which is completely independent of the spatial coordinates.
Sorli explained that this idea that both photon clocks tick at the same rate is not at odds with the experiments with flying clocks and other tests that have measured time dilation.
This difference, he says, is due to a difference between photon clocks and atom-based clocks. GPS confirms that clocks in orbit stations have different rates from the clocks on the surface of the planet, and this difference is valid for observers that are on the orbit station and on the surface of the planet. So interpreted, 'time dilatation' does not require 'length contraction,' which as we show in our paper leads to a contradiction by the light clocks differently positioned in a moving inertial system.
They note that other researchers have investigated abolishing the idea of spacetime in favor of separate space and time entities, but often suggest that this perspective is best formulated within the framework of an ether, a physical medium permeating all of space.
Scientists suggest spacetime has no time dimension
In contrast, Sorli and Fiscaletti think that the idea can be better modeled within the framework of a 3D quantum vacuum. Rather than viewing space as a medium that carries light, light's propagation is governed by the electromagnetic properties the permeability and permittivity of the quantum vacuum. This model gives exact calculations for the Mercury perihelion precession as calculations of the general theory of relativity.
Amrit Sorli and Davide Fiscaletti.