### Spacetime - Wikipedia

Here is a good summary of space time relationship through the period with different If you meant the latter - then yes, Time can be considered as a fully. Dec 2, I've been thinking about the physics of space and time for a little more than Yes , one can find rules that give behavior which on a large scale. Mar 30, The theory of special relativity explains how space and time are linked for . So yes, when astronaut Scott Kelly spent nearly a year aboard the.

Reference frames are inherently nonlocal constructs, and according to this usage of the term, it does not make sense to speak of an observer as having a location. Any specific location within the lattice is not important. The latticework of clocks is used to determine the time and position of events taking place within the whole frame. The term observer refers to the entire ensemble of clocks associated with one inertial frame of reference.

A real observer, however, will see a delay between the emission of a signal and its detection due to the speed of light. To synchronize the clocks, in the data reduction following an experiment, the time when a signal is received will be corrected to reflect its actual time were it to have been recorded by an idealized lattice of clocks.

In many books on special relativity, especially older ones, the word "observer" is used in the more ordinary sense of the word. It is usually clear from context which meaning has been adopted. Physicists distinguish between what one measures or observes after one has factored out signal propagation delaysversus what one visually sees without such corrections.

History of special relativity and History of Lorentz transformations Figure Michelson and Morley expected that motion through the aether would cause a differential phase shift between light traversing the two arms of their apparatus. The most logical explanation of their negative result, aether dragging, was in conflict with the observation of stellar aberration.

By the mids, various experiments such as the observation of the Arago spot a bright point at the center of a circular object's shadow due to diffraction and differential measurements of the speed of light in air versus water were considered to have proven the wave nature of light as opposed to a corpuscular theory.

Scientists have actually proved this phenomenon by sending atomic clocks up with high-speed rocket ships. They returned to Earth slightly behind the clocks on the ground. What does this mean for the Captain Kirk and his team? The closer an object gets to the speed of light, that object actually experiences time at a significantly slower rate. If the Enterprise were traveling safely at close to the speed of light to the center of our galaxy from Earth, it would take 25, years of Earth time.

For the crew, however, the trip would probably only take 10 years. Although that timeframe might be possible for the individuals onboard, we're presented with yet another problem -- a Federation attempting to run an intergalactic civilization would run into some problems if it took 50, years for a starship to hit the center of our galaxy and come back. So the Enterprise has to avoid the speed of light in order to keep the passengers onboard in synch with Federation time.

At the same time, it also must reach speeds faster than that of light in order to move around the universe in an efficient manner. In the usual formulation of physics, space is a backdrop, on top of which all the particles, or strings, or whatever, exist.

But that gets pretty complicated.

### Einstein's Theory of Special Relativity

As it happens, in his later years, Einstein was quite enamored of this idea. He thought that perhaps particles, like electrons, could be associated with something like black holes that contain nothing but space. But within the formalism of General Relativity, Einstein could never get this to work, and the idea was largely dropped. That was a time before Special Relativity, when people still thought that space was filled with a fluid-like ether. Meanwhile, it had been understood that there were different types of discrete atoms, corresponding to the different chemical elements.

And so it was suggested notably by Kelvin that perhaps these different types of atoms might all be associated with different types of knots in the ether.

It was an interesting idea. Maybe all that has to exist in the universe is the network, and then the matter in the universe just corresponds to particular features of this network. Even though every cell follows the same simple rules, there are definite structures that exist in the system—and that behave quite like particles, with a whole particle physics of interactions.

Back in the s, there was space and there was time. Both were described by coordinates, and in some mathematical formalisms, both appeared in related ways. It makes a lot of sense in the formalism of Special Relativity, in which, for example, traveling at a different velocity is like rotating in 4-dimensional spacetime.

So how does that work in the context of a network model of space? And then one just has to say that the history of the universe corresponds to some particular spacetime network or family of networks. Which network it is must be determined by some kind of constraint: But this seems very non-constructive: And, for example, in thinking about programs, space and time work very differently.

In a cellular automaton, for example, the cells are laid out in space, but the behavior of the system occurs in a sequence of steps in time. How does this network evolve? But now things get a bit complicated. Because there might be lots of places in the network where the rule could apply.

So what determines in which order each piece is handled? In effect, each possible ordering is like a different thread of time. And one could imagine a theory in which all threads are followed—and the universe in effect has many histories.

And to understand this, we have to do something a bit similar to what Einstein did in formulating Special Relativity: Needless to say, any realistic observer has to exist within our universe. So if the universe is a network, the observer must be just some part of that network.

Now think about all those little network updatings that are happening.

If you trace this all the way through —as I did in my book, A New Kind of Science —you realize that the only thing observers can ever actually observe in the history of the universe is the causal network of what event causes what other event.

Causal invariance is an interesting property, with analogs in a variety of computational and mathematical systems—for example in the fact that transformations in algebra can be applied in any order and still give the same final result. Here, as I figured out in the mids, something exciting happens: In other words, even though at the lowest level space and time are completely different kinds of things, on a larger scale they get mixed together in exactly the way prescribed by Special Relativity.

But because of causal invariance, the overall behavior associated with these different detailed sequences is the same—so that the system follows the principles of Special Relativity. At the beginning it might have looked hopeless: But it works out. Here the news is very good too: The whole story is somewhat complicated.

## How Warp Speed Works

First, we have to think about how a network actually represents space. Now remember, the network is just a collection of nodes and connections. Just start from a node, then look at all nodes that are up to r connections away. If the network behaves like flat d-dimensional space, then the number of nodes will always be close to rd.

One has to look at shortest paths—or geodesics—in the network. One has to see how to do everything not just in space, but in networks evolving in time. And one has to understand how the large-scale limits of networks work. But the good news is that an incredible range of systems, even with extremely simple rules, work a bit like the digits of piand generate what seems for all practical purposes random.

I think this is pretty exciting. Which means that these simple networks reproduce the features of gravity that we know in current physics.