Best Astronomy and Astrophysics Books to Read in
Books; Blogs Space‐Time, 'Science' and the Relationship between Physical Geography and Human Geography geography apart for so long has been their relationship to physics as an assumed model of 'science'. And, while some of the terms and scientific concepts in the book might "A Briefer History of Time," published first in in collaboration with . focus is on Tarter: her childhood relationships with her parents that helped. This book is about the nature of time, the beginning of the universe, and the tackling are ancient and honorable ones: Where did time and space come from? and behavioral science to optimize our relationship with time.
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.
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. 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.
Space, Time, and the Use of Language
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. Clearly, the author is no historian. This is a deeply flawed statement: If two events are causally connected if one lies within the light cone of the other the causal order is preserved in all frames of reference.
The author confuses this with relativity of simultaneity, which is the concept that distant simultaneity — whether two spatially separated events occur at the same time— is not absolute, but depends on the observer's reference frame.
Moreover, special relativity does NOT mean arbitrary subjectivity, as each frame of reference can be mathematically translated into another frame with the appropriate Lorentz transformation. And in any case, of course any agent carrying out any sort of activity "creates reality" - the action of the agent certainly influences it - and so what? It is not possible to be in a rest frame of a photon. Also, I would question how sensical it actually is to consider a case where the Lorentz conversion factor "gamma" goes to infinity — when you get infinity values you have to be very careful before making any assumptions and taking any conclusions.
You can say, in a metaphorical sense, that the photon "experiences no time", but even assuming that this is a meaningful statement we also need to take into account that, within the same considerations, that the photon travels zero distance; so the whole example is very dangerous and prone to misconception. Yes, you can always say that you can assume that you are traveling at speed asymptotically close to "c", but the whole example in any case seems preposterous and very forced.
By the way, such examples of "simultaneity" can be seen in the cave paintings of the Lascaux Cave - does it mean that our artistically gifted human ancestors had some form of special relativity pre-cognition more than 20, years ago? What does this actually mean?
Art and Physics: Parallel Visions in Space, Time, and Light by Leonard Shlain
Does really a Cubist painting represent in a more informative way, or has more explanatory power, than language, when it comes to the tenets of relativity, such as Lorentz invariance?
In my opinion this statement, in its generality, is virtually meaningless. Has the author ever heard of Stalingrad? Does he not know who was the actual major contributor to the defeat of Germany?
Well, this is definitely a highly speculative hypothesis which has never been corroborated by even the flimsiest shred of evidence, and something against the current consensus - page This statement demands some serious clarification.
One day he was looking out of his office window and imagined someone falling off the roof of a nearby building. Einstein realized that, while falling, that person would feel weightless. Please do not try jumping off a building to test this, though. To someone on the ground, gravity would appear to make the person fall faster and faster.
Space and Time, Matter and Mind: The Relationship Between Reality and Space-Time
In other words, the speed of their fall would accelerate. Gravity, Einstein suddenly realized, was the same thing as acceleration! Imagine standing on the floor of a rocket ship. There are no windows. You feel your weight against the floor. If you try to lift your foot, it wants to go back down. So maybe your ship is on the ground. But it is also possible that your ship might be flying. If it is moving upward at a faster and faster speed — accelerating smoothly by just the right amount — your feet will feel pulled to the floor just as they had when the ship was sitting on the ground.
Once Einstein realized that gravity and acceleration are one and the same, he thought he could find a new theory of gravity.
He just had to find the math that would describe any possible acceleration for any object. In other words, no matter how the motions of objects appeared from one point of view, you would have a formula to describe them just as correctly from any other point of view.
Finding that formula did not prove easy.
Imagine an ant walking across a sheet of paper without changing direction. Its path should be straight. The same thing happens to a beam of light in space. That flat-paper math is known as Euclidean geometry. It describes things like shapes made from segments of lines and angles where lines cross. And it works fine on flat surfaces, but not on bumpy surfaces or curved surfaces such as the outside of a ball.
So Einstein needed a new kind of geometry.Is Gravity An Illusion? - Space Time - PBS Digital Studios
Luckily, some mathematicians had already invented what he needed. It is called, not surprisingly, non-Euclidean geometry.
So he got help from a math teacher from his school days. With his new knowledge about this improved geometry, Einstein was now able to move ahead. Until he got stuck again. That new math worked for many points of view, he found, but not all possible ones. He concluded that this was the best he — or anybody — could do. Or so he thought. But then he got a new job.
He moved to Berlin, to a physics institute where he did not have to teach.
He could spend all of his time thinking about gravity, undistracted. And, here, inhe saw a way to make his theory work. In November, he wrote four papers outlining the details. He presented them to a major German science academy. The really big picture Soon afterwards, Einstein began thinking about what his new theory of gravity would mean for understanding the whole universe.