the abstract data types supporting space and time description. Section 4 discusses are devoted to the definition of object and relationship types, respectively. Space and time are to space-time what arms and legs are to humans. In some sense they are interchangeable, but you cannot understand 10, years of. Examples of poor database design are all too common. Figure 1 shows the different types of relationship in a diagramatic form which are discussed This helps to save disk space on the computer, minimise data entry time, and break down.
The series of events can be linked together to form a line which represents a particle's progress through spacetime. That line is called the particle's world line. It was only with the advent of sensitive scientific measurements in the mids, such as the Fizeau experiment and the Michelson—Morley experimentthat puzzling discrepancies began to be noted between observation versus predictions based on the implicit assumption of Euclidean space.
Each location in spacetime is marked by four numbers defined by a frame of reference: The 'observer' synchronizes the clocks according to their own reference frame. In special relativity, an observer will, in most cases, mean a frame of reference from which a set of objects or events are being measured. This usage differs significantly from the ordinary English meaning of the term.
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. Foreign keys are columns in a table which provide a link to another table. In our geographical example, the county column in our table of towns provides a link to the table of counties, and is thus a key field in that relationship.
It is very important therefore to ensure that entries in the both tables are identical, that both tables use the full county name Hertfordshire or an abbreviation Herts but not a mixture of the two. There is one final complexity which must be addressed. What could we do in the case where there are two towns with the same name in the same county? Although in our example it is unlikely, in databases of other information this could happen.Relationship expert: Needing space is not a bad thing
We could use a combination of name, county and population as the primary key for the table of towns. If we had a table of shops, we would have to include the town name, county and the population to provide a link between the two tables. This, however, will re-introduce the problem of data redundancy. A better course of action is to assign a unique code to each town, and to use this code as the link to the table of shops.
The use of codes has other advantages: These codes can be assigned by the user, WGC for Welwyn Garden City, or could be a sequential number created automatically by the program.
What Is Spacetime, Really?
Data types and definition The data stored in tables can be classified into types. This is an alphanumeric data type, also known as a string or character field. The third column for population contains a number and is a numeric data type. There are other data types such as date or even images and sounds.
The type of data is important as different types of data behave in different ways. A good example is the sorting order of a series of numbers. If we store 1, 22, 3, 10, 2 and 15 in a numeric column, and ask the program to sort the rows of the table on this column, we will get 1, 2, 3, 10, 15, 22 as we might expect. If that column was defined as an alphanumeric data type, the result would be 1, 10, 15, 2, 22, 3, a rather different result!
Different DMSs have different ways of handling different types of data see below. Each column of data also has to be defined. We also have to decide what the entries mean, in the table of counties we have a column for area--we have to decide if this is the area in square miles or square kilometers.
We may wish to restrict the possible entries in a column. We can do this to prevent errors, we may decide that the maximum allowed population in a town is 10, as no town in Britain has a population larger than that. We may also wish to restrict entries to a limited list of terms.
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. 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?
What Is Spacetime, Really?—Stephen Wolfram Blog
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.
An introduction to databases
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.