Einstein's Theory of General Relativity: A Simplified Explanation
Define space-time. space-time synonyms, space-time pronunciation, space-time translation, English dictionary definition of space-time. or n physics the. I've been thinking about the physics of space and time for a little more And all that's intrinsically defined in the graph is the pattern of these. Albert Einstein determined that massive objects cause a distortion in space-time, which is felt as gravity.
Somehow all these things have to emerge from something much lower level and more fundamental. But even though such a structure works well for models of many thingsit seems at best incredibly implausible as a fundamental model of physics.
I thought about this for years, and looked at all sorts of computational and mathematical formalisms. A network—or graph —just consists of a bunch of nodes, joined by connections. Space as a Network So could this be what space is made of? But do we in fact know that space is continuous like this?
In the early days of quantum mechanics, it was actually assumed that space would be quantized like everything else. But what if space—perhaps at something like the Planck scale—is just a plain old network, with no explicit quantum amplitudes or anything?
But how could this be what space is made of? First of all, how could the apparent continuity of space on larger scales emerge? On a small scale, there are a bunch of discrete molecules bouncing around.
But the large-scale effect of all these molecules is to produce what seems to us like a continuous fluid. It so happens that I studied this phenomenon a lot in the mids—as part of my efforts to understand the origins of apparent randomness in fluid turbulence.
What about all the electrons, and quarks and photons, and so on? 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. As it happens, in his later years, Einstein was quite enamored of this idea.
Einstein's Theory of General Relativity
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.
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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. 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.
What Is Spacetime, Really?—Stephen Wolfram Blog
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. There are all sorts of technical things to say, not suitable for this general blog.
Quite a few of them I already said long ago in A New Kind of Science —and particularly the notes at the back. A few things are perhaps worth mentioning here.
All these things have to emerge. When it comes to deriving the Einstein Equations, one creates Ricci tensors by looking at geodesics in the network, and looking at the growth rates of balls that start from each point on the geodesic.
The Einstein Equations one gets are the vacuum Einstein Equations. One puts remarkably little in, yet one gets out that remarkable beacon of 20th-century physics: Particles, Quantum Mechanics, Etc.
Another very important part is quantum mechanics.
Space-time - Simple English Wikipedia, the free encyclopedia
But then their behavior must follow the rules we know from quantum mechanics—or more particularly, quantum field theory. A key feature of quantum mechanics is that it can be formulated in terms of multiple paths of behavior, each associated with a certain quantum amplitude. It's important to understand Einstein's work on the space-time continuum and how it relates to the Enterprise traveling through space.
In his Special Theory of RelativityEinstein states two postulates: The speed of light about , meters per second is the same for all observers, whether or not they're moving. Anyone moving at a constant speed should observe the same physical laws. Putting these two ideas together, Einstein realized that space and time are relative -- an object in motion actually experiences time at a slower rate than one at rest. Although this may seem absurd to us, we travel incredibly slow when compared to the speed of light, so we don't notice the hands on our watches ticking slower when we're running or traveling on an airplane.
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?Time & Space: Concept or Reality? - Sadhguru
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.