What is space/time: Definition and 26 Discussions

In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why different observers perceive differently where and when events occur.
Until the 20th century, it was assumed that the three-dimensional geometry of the universe (its spatial expression in terms of coordinates, distances, and directions) was independent of one-dimensional time. The physicist Albert Einstein helped develop the idea of spacetime as part of his theory of relativity. Prior to his pioneering work, scientists had two separate theories to explain physical phenomena: Isaac Newton's laws of physics described the motion of massive objects, while James Clerk Maxwell's electromagnetic models explained the properties of light. However, in 1905, Einstein based a work on special relativity on two postulates:

The laws of physics are invariant (i.e., identical) in all inertial systems (i.e., non-accelerating frames of reference)
The speed of light in vacuum is the same for all inertial observers, regardless of the motion of the light source.The logical consequence of taking these postulates together is the inseparable joining of the four dimensions—hitherto assumed as independent—of space and time. Many counterintuitive consequences emerge: in addition to being independent of the motion of the light source, the speed of light is constant regardless of the frame of reference in which it is measured; the distances and even temporal ordering of pairs of events change when measured in different inertial frames of reference (this is the relativity of simultaneity); and the linear additivity of velocities no longer holds true.
Einstein framed his theory in terms of kinematics (the study of moving bodies). His theory was an advance over Lorentz's 1904 theory of electromagnetic phenomena and Poincaré's electrodynamic theory. Although these theories included equations identical to those that Einstein introduced (e.g., the Lorentz transformation), they were essentially ad hoc models proposed to explain the results of various experiments—including the famous Michelson–Morley interferometer experiment—that were extremely difficult to fit into existing paradigms.
In 1908, Hermann Minkowski—once one of the math professors of a young Einstein in Zürich—presented a geometric interpretation of special relativity that fused time and the three spatial dimensions of space into a single four-dimensional continuum now known as Minkowski space. A key feature of this interpretation is the formal definition of the spacetime interval. Although measurements of distance and time between events differ for measurements made in different reference frames, the spacetime interval is independent of the inertial frame of reference in which they are recorded.Minkowski's geometric interpretation of relativity was to prove vital to Einstein's development of his 1915 general theory of relativity, wherein he showed how mass and energy curve flat spacetime into a pseudo-Riemannian manifold.

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  1. shunyadragonvv

    I Quantum decoherence and the emergence of space/time and gravity

    Quantum decoherence. and the emergence of continuous space/time and gravity In another forum I have experienced a lot of combative dialogue asserting that continuous time/space is a property of the smallest Quantum scale. My present knowledge indicates this not true, and that the goal of the...
  2. B

    What is the true composition of a space/time vacuum?

    Thought experiment for discussion: You have a sealed transparent container with a "perfect vacuum" inside of it. 1) List what is inside of the "empty" container. 2) Explain how you might go about expelling EVERYTHING from the container.
  3. seb7

    Is the speed of light truly constant in all directions?

    Something that's been bugging me, but unable to find an answer for.. The speed of light (in a vacuum) is absolute, well not really, its relative to the space/time its in. ie. The distant galaxies are moving away from us, but their local light speed is relative to their space/time. So since...
  4. L

    Does Spaghettification contradict space/time swap in a black hole

    Hi, I've heard and read that if someone was to fall towards a black hole, say feet first, they would undergo spaghettification at a certain distance, as the gravity at their feet would be much greater than the gravity at their head, and their body wouldn't be able to reisist the pulling effect...
  5. E

    Space/time curvature of the young universe?

    All over the news we see the results of the recent detection of gravity waves from the early universe. Which got me wondering: The early universe was much more dense than at the present. It therefore seems that spacetime was much more curved than it is, on average, today. Is this...
  6. S

    How Does the Loaf of Bread Model Explain Space-Time Perception?

    Perhaps I am red-shifted, but I just saw a video demonstrating space/time as a loaf of bread and depending on how it is "sliced" an observer would see different times across space. I am having a hard time wrapping my head around this theory. I can see how an observer from afar would see my past...
  7. B

    Why Does Space/Time Not Cause Friction?

    I started general last year and I was wondering why space/time does not cause fricton. Since it has such an effect on large bodies such as our solar system that occupy space in it and with the cassamir effect we know a vacuum can interact with matter under the right conditions. It just seems...
  8. G

    Reading material re space/time

    as title.. are there any books with recent info re. current thinking about space/time..origin, structure etc... cheers
  9. R

    RELATIVE Space/Time and Lightspeed question

    Hey everyone, First off I am not a physics major or a math guru. Physics has always been some thing that I have been interested in though. Physical science and the way things work has always interested me. I mention this, because I do not want to come off sounding like an idiot. I know most...
  10. M

    Thoughts on Space/Time and Gravity

    Some of my thoughts on space theory. I see many similarities between space/time and water. Just how they both move and flow. Only one thing is faster than light and that is the expansion of space/time it self. We have discovered that space is expanding faster and faster. This is the reason why...
  11. mishima

    What makes space and time exist?

    I just read an amazing book called "The Existence of Space and Time" by Ian Hinckfuss (Oxford Press, 1975). Philosophy of physics behind space and time. It is also somewhat covertly about relativity. Very short, very readable (based on lectures given), super clear. It also has very nice...
  12. N

    Space/time expansion and quantum world

    as predicted by red shift's measurement the galaxies seems to be going away from us how is this expansion be seen in quantum scale?
  13. T

    So if space/time is a plain

    So if space/time is a "plain"... from what i get of it, space and time is a flat surface, and the planets and what not ride along the rings of the depressions made in it. The more i'd guess "dense" a object is, the bigger the depression and the higher gravitational pull it has. Now how in the...
  14. C

    Curvature of space/time question/problem

    While watching a video on youtube about space/time, it explained space/time like a fabric with a ball on it. Rolling another ball past this first ball caused the second ball to curve. I get that part. then they said that Arthur Eddington went to test general relativity by photographing a...
  15. atyy

    Emergent Space/Time: AdS/CFT and dS/CFT

    https://www.physicsforums.com/showpost.php?p=3263502&postcount=94 Actually, thinking even about AdS/CFT which is commonly said to be emergent space, but not emergent time, if the bulk geometry is pseudo-Riemannian, which has multiple timelike directions at each point, shouldn't time emerge too?
  16. A

    Conditions for translational invariance in space/time for a 2-point function?

    Hi, Assume the following action: \int d^4 x L[\phi,A]+ \int d^4 x A_{\mu} (x) J^{\mu}(x) What are the conditions on the form of action to have space/time translational invariance for a two point function: \left\langle J_{\mu}(x) J_{\nu}(y) \right\rangle = G_{\mu \nu}(x-y)...
  17. P

    Inflation or normal space/time misunderstood?

    Please forgive my ignorance but: I am trying very hard to understand how expanding space works. The problems I have are: 1. If expanding space has enough "connection" (friction?) to pull galaxies apart then it should also have a resistance to planets in orbit, rockets continuing on their...
  18. M

    Mass moving through Space/Time = Gravity?

    Hello, I've wondered about this idea before, and thought I would put this together and get some opinions. When it comes to electricity and magnetism, electricity can generate magnetism, and a moving magnet can generate an electric current. When it comes to mass, gravity, and space/time...
  19. H

    Where did Einstein say :mass curve space/time ?

    I'm reading GR on http://www.bartleby.com/173/29.html" quoting "Hereupon we introduce a hypothesis: that the influence of the gravitational field on measuring-rods, clocks and freely-moving material points continues to take place according to the same laws, even in the case when the...
  20. Z

    How would you calculate how bodies curve space/time?

    Okay, I am really interested in relativity, but very ignorant in it also. I already know you would divide regular space/time by √(1 - rs/r) rs = schwarzschilds radius r = radius of object from center of mass How would we define regular space/time in an equation? What units or...
  21. F

    Is Gravity Linked to Quantum Entanglement?

    This may sound silly and completely wrong but: Could space/time and gravity be due to entanglement of atoms all pulling on each other? and the same theory for dark matter? This would also suggest why some stars have greater gravitation due to the nuclear fusion which may cause more entanglement.
  22. J

    The Unity of the Dualities? Wave/Partice Duality, Space/Time Duality, and Energy/Mass

    Does any theory explain all these dualities: Wave/Particle Duality, Space/Time Duality, and Energy/Mass Duality. Does ST or LQG account for all these dualities? What I mean is, can ST or LQG show that these dualities are unified by some deeper physical model? Can any theory show that...
  23. D

    Understanding Space and Time Warping with Velocity: A Quantum Perspective

    I’m trying to think of an easier way to describe how space and time will warp with velocity. This is only an analogy and since I’m not a physicist or mathematician I don’t have the ability to compare the resulting equations to Einstein’s theory. I am not trying to disprove or refute anyone’s...
  24. J

    A possible view of curved space/time?

    Hi all, Is this a valid view of space/time curvature. The path of an object under influence of a force has a curved trajectory in inertial space/time. Therefore, the inertial axes appear curved to an observer traveling on the curved trajectory. In the same way, an observer in a...
  25. L

    Is Life an Anti-Entropic Zone in the Fabric of Space/Time?

    Can we say that non-linear fabric of space/time (n_Dim fabric that is curved toward n+1_Dim) is an anti-entropic zone? And if so, can we understand life phenomena as an anti-entropic zone that can duplicate itself?
  26. P

    Conceptional space/time cosmology

    In this theory a theoretical model is constructed for observation. (This is the first of a series) A: Space devoid of matter. B: Matter devoid of space. C: Space and Matter. In reply to "A" Is absolute space possible, a void with non-existing matter? has it been proven? can it...