Philosophy of space and time - Wikipedia
Space-time, in physical science, single concept that recognizes the union of one-dimensional continuum, completely homogeneous along its infinite extent. Every set of coordinates, or particular space-time event, in such a universe is. Philosophy of space and time is the branch of philosophy concerned with the issues In contrast to ancient Greek philosophers who believed that the universe had an infinite past with no beginning, medieval philosophers and . Leibniz describes a space that exists only as a relation between objects, and which has no. Space and time are independent in Newtonian physics. The spatial The Universe . It means gravitational influences should travel with infinite speed. But that.
As physicist Enrico Prati noted in a recent study, Hamiltonian dynamics equations in classical mechanics is robustly well-defined without the concept of absolute time.
The scientists also investigated the falsifiability of the two notions of time. The concept of time as the fourth dimension of space - as a fundamental physical entity in which an experiment occurs - can be falsified by an experiment in which time does not exist, according to the scientists.
An example of an experiment in which time is not present as a fundamental entity is the Coulomb experiment; mathematically, this experiment takes place only in space. On the other hand, in the concept of time as a numerical order of change taking place in space, space is the fundamental physical entity in which a given experiment occurs. Although this concept could be falsified by an experiment in which time measured by clocks is not the numerical order of material change, such an experiment is not yet known.
On the basis of experimental data, time is what we measure with clocks: In this paradox, the faster Achilles gives the Tortoise a head start in the race.
So whenever Achilles reaches a point where the Tortoise has been, the Tortoise has also moved slightly ahead. Although the conclusion that Achilles can never surpass the Tortoise is obviously false, there are many different proposed explanations for why the argument is flawed. Here, the researchers explain that the paradox can be resolved by redefining velocity, so that the velocity of both runners is derived from the numerical order of their motion, rather than their displacement and direction in time.
From this perspective, Achilles and the Tortoise move through space only, and Achilles can surpass Tortoise in space, though not in absolute time. The researchers also briefly examine how this new view of time fits with how we intuitively perceive time. Many neurological studies have confirmed that we do have a sense of past, present, and future. However, some recent studies have challenged this traditional view, and suggest that the brain represents time in a spatially distributed way, by detecting the activation of different neural populations.
To account for the curve that we observe, an increase in the number of objects in the universe also increases the curvature in the water. Mach argued that the momentum of an object, whether angular or linear, exists as a result of the sum of the effects of other objects in the universe Mach's Principle. Einstein[ edit ] Albert Einstein proposed that the laws of physics should be based on the principle of relativity.
This principle holds that the rules of physics must be the same for all observers, regardless of the frame of reference that is used, and that light propagates at the same speed in all reference frames.
This theory was motivated by Maxwell's equationswhich show that electromagnetic waves propagate in a vacuum at the speed of light.
However, Maxwell's equations give no indication of what this speed is relative to. Prior to Einstein, it was thought that this speed was relative to a fixed medium, called the luminiferous ether. In contrast, the theory of special relativity postulates that light propagates at the speed of light in all inertial frames, and examines the implications of this postulate.
All attempts to measure any speed relative to this ether failed, which can be seen as a confirmation of Einstein's postulate that light propagates at the same speed in all reference frames. Special relativity is a formalization of the principle of relativity that does not contain a privileged inertial frame of reference, such as the luminiferous ether or absolute space, from which Einstein inferred that no such frame exists.
Einstein generalized relativity to frames of reference that were non-inertial. He achieved this by positing the Equivalence Principlewhich states that the force felt by an observer in a given gravitational field and that felt by an observer in an accelerating frame of reference are indistinguishable.Is the Universe Infinite?
This led to the conclusion that the mass of an object warps the geometry of the space-time surrounding it, as described in Einstein's field equations. In classical physics, an inertial reference frame is one in which an object that experiences no forces does not accelerate.
In general relativity, an inertial frame of reference is one that is following a geodesic of space-time. An object that moves against a geodesic experiences a force.
An object in free fall does not experience a force, because it is following a geodesic. An object standing on the earth, however, will experience a force, as it is being held against the geodesic by the surface of the planet.
Einstein partially advocates Mach's principle in that distant stars explain inertia because they provide the gravitational field against which acceleration and inertia occur. But contrary to Leibniz's account, this warped space-time is as integral a part of an object as are its other defining characteristics, such as volume and mass.
If one holds, contrary to idealist beliefs, that objects exist independently of the mind, it seems that relativistics commits them to also hold that space and temporality have exactly the same type of independent existence.
Conventionalism[ edit ] The position of conventionalism states that there is no fact of the matter as to the geometry of space and time, but that it is decided by convention. This view was developed and updated to include considerations from relativistic physics by Hans Reichenbach. Reichenbach's conventionalism, applying to space and time, focuses around the idea of coordinative definition. Coordinative definition has two major features. The first has to do with coordinating units of length with certain physical objects.
This is motivated by the fact that we can never directly apprehend length. Instead we must choose some physical object, say the Standard Metre at the Bureau International des Poids et Mesures International Bureau of Weights and Measuresor the wavelength of cadmium to stand in as our unit of length. The second feature deals with separated objects.
Although we can, presumably, directly test the equality of length of two measuring rods when they are next to one another, we can not find out as much for two rods distant from one another. Even supposing that two rods, whenever brought near to one another are seen to be equal in length, we are not justified in stating that they are always equal in length. This impossibility undermines our ability to decide the equality of length of two distant objects.
Sameness of length, to the contrary, must be set by definition. Such a use of coordinative definition is in effect, on Reichenbach's conventionalism, in the General Theory of Relativity where light is assumed, i. After this setting of coordinative definition, however, the geometry of spacetime is set. Structure of space-time[ edit ] This section and every subsection does not cite any sources.
Please help improve this section and every subsection by adding citations to reliable sources. Unsourced material may be challenged and removed. August Learn how and when to remove this template message Building from a mix of insights from the historical debates of absolutism and conventionalism as well as reflecting on the import of the technical apparatus of the General Theory of Relativity, details as to the structure of space-time have made up a large proportion of discussion within the philosophy of space and time, as well as the philosophy of physics.
The following is a short list of topics. Relativity of simultaneity[ edit ] According to special relativity each point in the universe can have a different set of events that compose its present instant. This has been used in the Rietdijk—Putnam argument to demonstrate that relativity predicts a block universe in which events are fixed in four dimensions.
Invariance, or symmetry, applies to objects, i. Covariance applies to formulations of theories, i. This distinction can be illustrated by revisiting Leibniz's thought experiment, in which the universe is shifted over five feet. In this example the position of an object is seen not to be a property of that object, i.
Similarly, the covariance group for classical mechanics will be any coordinate systems that are obtained from one another by shifts in position as well as other translations allowed by a Galilean transformation. In the classical case, the invariance, or symmetry, group and the covariance group coincide, but they part ways in relativistic physics.
The symmetry group of the general theory of relativity includes all differentiable transformations, i. The formulations of the general theory of relativity, unlike those of classical mechanics, do not share a standard, i. As such the covariance group of the general theory of relativity is just the covariance group of every theory.
Historical frameworks[ edit ] A further application of the modern mathematical methods, in league with the idea of invariance and covariance groups, is to try to interpret historical views of space and time in modern, mathematical language. In these translations, a theory of space and time is seen as a manifold paired with vector spacesthe more vector spaces the more facts there are about objects in that theory.
The historical development of spacetime theories is generally seen to start from a position where many facts about objects are incorporated in that theory, and as history progresses, more and more structure is removed. For example, Aristotelian space and time has both absolute position and special places, such as the center of the cosmos, and the circumference.
Newtonian space and time has absolute position and is Galilean invariantbut does not have special positions. Holes[ edit ] With the general theory of relativity, the traditional debate between absolutism and relationalism has been shifted to whether spacetime is a substance, since the general theory of relativity largely rules out the existence of, e.
One powerful argument against spacetime substantivalismoffered by John Earman is known as the " hole argument ". This is a technical mathematical argument but can be paraphrased as follows: Define a function d as the identity function over all elements over the manifold M, excepting a small neighbourhood H belonging to M. Over H d comes to differ from identity by a smooth function. These considerations show that, since substantivalism allows the construction of holes, that the universe must, on that view, be indeterministic.
Which, Earman argues, is a case against substantivalism, as the case between determinism or indeterminism should be a question of physics, not of our commitment to substantivalism.
Direction of time[ edit ] The problem of the direction of time arises directly from two contradictory facts. Firstly, the fundamental physical laws are time-reversal invariant ; if a cinematographic film were taken of any process describable by means of the aforementioned laws and then played backwards, it would still portray a physically possible process.
Secondly, our experience of time, at the macroscopic level, is not time-reversal invariant. We have memories of the past, and none of the future.
We feel we can't change the past but can influence the future. Causation solution[ edit ] One solution to this problem takes a metaphysical view, in which the direction of time follows from an asymmetry of causation.
We know more about the past because the elements of the past are causes for the effect that is our perception. We feel we can't affect the past and can affect the future because we can't affect the past and can affect the future. There are two main objections to this view.
First is the problem of distinguishing the cause from the effect in a non-arbitrary way. The use of causation in constructing a temporal ordering could easily become circular.
Is the universe moving through infinite space time as it expands? - Astronomy Stack Exchange
The second problem with this view is its explanatory power. While the causation account, if successful, may account for some time-asymmetric phenomena like perception and action, it does not account for many others. However, asymmetry of causation can be observed in a non-arbitrary way which is not metaphysical in the case of a human hand dropping a cup of water which smashes into fragments on a hard floor, spilling the liquid. In this order, the causes of the resultant pattern of cup fragments and water spill is easily attributable in terms of the trajectory of the cup, irregularities in its structure, angle of its impact on the floor, etc.
However, applying the same event in reverse, it is difficult to explain why the various pieces of the cup should fly up into the human hand and reassemble precisely into the shape of a cup, or why the water should position itself entirely within the cup.