# What is Space time: Definition and 162 Discussions

In physics, spacetime is any mathematical model which fuses the three dimensions of space and the 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 famous physicist Albert Einstein helped develop the idea of space-time 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, Albert 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 a vacuum is the same for all observers, regardless of the motion of the light source.The logical consequence of taking these postulates together is the inseparable joining together 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 (i.e., 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. ### A Current status of Tom Banks' Holographic space time?

Interested in Banks' HST these days, for discussion,here are some abstract and an email from L.Smolin. A recent conclusive paper as well https://arxiv.org/abs/2201.06988 The formalism of Holographic Space-time (HST) is a translation of the principles of Lorentzian geometry into the language...
2. ### A B and A in Curved Space Time: Does \nabla \times A =B?

By definition of the vector potential we may write \nabla \times A =B at least in flat space. Does this relation hold in curved space? I am particularly interested if we can still write this in a spatially flat Friedmann-Robertson-Walker background with metric ds^2=dt^2-a^2(dx^2+dy^2+dz^2) and...
3. ### I Position Vector in Curved Space Time: Explained

It is said that: It is not possible to write a position vector in a curved space time. What is the reason? How can one describe a general vector in a curved space time? Can you please suggest a good textbook or an article which explains this aspect?
4. ### B Gravitational Wave System and Locations

My hypothesis: A sequence with the gravitational waves detected, sent by modulating radio waves, could be received and used by other intelligent beings to find the corresponding sequence within their records and then compare it to calculate our spacetime position in relation to theirs. As...
5. ### I Possible webpage title: Is There an Upper Limit to the Size of a Black Hole?

Presume we look at a two-dimensional view of space time, with no local masses, and we draw a grid of equidistance spaced lines. The intent is to look at space but not time. As we begin, we look in all directions and the grid lines are evenly spaced. Begin adding mass to the center of the grid...
6. ### B Space + time = space time? then....

probably a daft question asked before, but. if space is expanding at an accelerating rate would that mean time is accelerating too?. after all Einstein* claims and the maths seems to say that space and time are the same thing, ie space-time. so if space is expanding faster and faster shouldn't...
7. ### B LIGO and space time changes

Sorry if the question has been already answered, but I didn't manage to find it. Let's go back to ligo detection of gravitational waves, my question is the following: if space time changes its texture due to a gravitational effect, all the rulers (and clocks) in that spot will be affected, so...
8. ### I How Does the Metric of a 4-D Spacetime Define Its Symmetry and Expansion?

Our 4-D space is ##x^1,x^2,x^3 ,t##. Our sub-manifold is defined by ##(x^1,x^2,x^3)## Therefore for this sub-manifold to be maximally symmetric and for which the tangent vector ##\frac{∂}{∂t}(\hat t)## orthogonal to this sub-manifold The metric becomes...
9. ### A Dark matter and the fabric of space time,

{Moderator's note: Moved to Cosmology forum.] Dark matter and the fabric of space time, Can someone with a real knowledge base of physics and the current accepted theories, please explain why the fabric of space is not the candidate for the elusive dark matter? Having read extensively about...
10. ### B Space Time fabric graphic is misleading

This has been bothering me for some time, and would like to get a physicist's view of it. If my understanding or contention is in error, please correct me (gently). I only have under grad physics from 1970, and was a microbiologist, though am interested in quantum physics, cosmology. My...
11. ### I What is it that forces an object down curved space time?

To explain the concept of curved space time, we often use analogy of rubber sheet. If we put a heavy ball at the centre of sheet then it creates a depression and now a smaller ball will fall towards that heavy ball because of depression. But in this analogy smaller ball is falling down the slope...
12. ### B Expanding space time and Virtual particles

If space time (the universe) is infinitely expanding what happens when it rips? Have we observed Virtual particles in an area and counted them? Does the expansion of space time affect the amount of Virtual particles in a particular area? Is it theoretically possible to expand space time to a...
13. L

### I GR and its bending of space time

Hello Maybe my question is dumb but is the bent of space time instant due to gravity? If a mass pops into existence will space time be bent instantly ? Intercations between forces are light speed but gravity is and is not a force depending on pov
14. ### B How Planetary Bodies Affect Space Time

Hello. I was thinking about gravity and how matter bends the ST (space time) creating gravity.which lead on to singularities. I wondered how much mass it would take to either make a hole in spacetime, or how much it would take to make a black hole. So I googled it. This is where my confusion...
15. ### Can time be considered a direct function of movement?

Can it be said that time is directly related to movement? That is to say, on a quantum level, if all motion were to cease, would that not bring about the cessation of time?
16. ### A Space time expnasion, age of universe.

I was thinking about the age of the universe which is said to be 13.8 billion years approximately. I read that this is derived from two sources , calculating the life of the oldest stars in the observable universe and from extrapolating backwards the distance which is radius from Earth to all...
17. ### B Is Lorentz contraction explained by space time diagram ?

Is there a way to explain Lorentz contraction on space-time diagrams ? I cannot find a way by myself. Your teaching will be appreciated.
18. ### B Warping Spacetime: Classical Physics & Relativity

Based on classical physics all things attract one another due to their own gravity pull, so theoretically the Earth is drawn closer to a tennis ball even if its impossible to detect. Knowing this and Einsteins theory of relativity of spacetime could I not assume then that every physical body...
19. ### B Gravity: Why Objects Attract Towards Earth | Einstein

Why does an object is attracted towards Earth according to Einstein?? I only know that celestial objects are attracted due to curve made by another massive object but what happens in case of objects attached to Earth??[emoji26] [emoji26]
20. ### B Exploring a Micro Singularity in Euclidean Space Time

What if the LHC produced a mini black hole and as a result a micro singularity was produced. If you were using Euclidean space time what equations and factors do you think would be most relevant?
21. ### B How well is Time understood i. Space time?

I have been doing some reading and from what i inderstand of relativity(wich isn't much granted) it states that space and time can be viewed as a single entity that mass bends warps and affects in various ways. We have a pretty good understanding of how mass affects space in 3 dimensions. For...
22. ### B Length contraction vs Space time

Does length contraction means the contraction of space time?
23. ### B Why do objects always revolve around each other in space?

Dear PF Forum, I have a confusion about gravity. And frankly I don't know if this question belongs to this sub forum (cosmology, general physic?). Gravity attracts object - Newton Gravity curves space time - Einstein. Why we revolve around a massive object? Because that massive object curves...
24. ### B Just a Doubt -- can the Space Time Fabric be ripped or broken?

Hey, can the Space Time Fabric be ripped or broken? The answer could help find the state of the universe on some aspects.
25. ### I Effects of Stretching Space Time: Questions & Answers

Reading about gravity waves got me back to thinking about relativity. And I am left with two questions to which I don't know the answer... Question 1. Gravity waves ripple through the entire universe. They will not cause any macro scale effects because local changes to space-time are very...
26. ### Unlocking the Mystery of Space-Time Slow Zones

ok, sorry if i sound daft, but this one has been keeping me awake and i need a better physics brain to tell me why this is b'locks So, there was a recent study in aus that said Aliens don't exist, or rather that we can't find any evidence, because the conditions for life to evolve require...
27. ### I Exploring the Mystery of Space Time: Visualizing One Dimensional Strings

I've been wondering, space time is supposed to be consists of one dimensional string as described in the string theory, but how exactly does space time looks like since it is invisible to us. Is it possible to get a sketch of such one dimensional strings?
28. ### Faster Than Light Communication Through Space-Time Bubbles

I think we all know what an Alcubierre drive is, well this is similar in principle. Is it possible to conduct faster than light communication through the acceleration of a bubble of space time? is it even possible to do this without a ship, and just send it out as a warp bubble from a point like...
29. ### Integration by parts in curved space time

In this thread, ramparts asked how integration by parts could be used in general relativity. suppose you have ##\int_M (\nabla^a \nabla_a f) g .Vol## Can it be written like ##\int_M (\nabla^a \nabla_a g) f .Vol## plus a boundary integration term (by integrating twice by parts)? I think thay it...
30. ### Why Do We Feel Acceleration If Gravity Is Just Curvature of Space-Time?

If gravity is not a force, rather the curvature of space time influenced by a body's mass, then why do we perceive an acceleration due to gravity, as though there was a force? In my mind, it would make sense for the bend in space to only cause a massive object to change direction. I suppose if...
31. ### I Exploring Einstein's Theory of Gravity: Time Dilation and Tidal Forces

I have some questions related to this video: In the Einstein view of gravity, time is warped. Is this warped time same as the gravitational time dilation? In other words, is the curved time axis due to different clock speeds at different height in a gravitational field? Further, can the tidal...
32. ### Space-Time Curvature: Evidence of Mass Effect?

There exist evidence that space time fabric can be curved arround massive objects?
33. ### Why does warping space time still violate causality?

I am having a tough time getting my head around this. I get that traveling faster then c in itself has an effect on the the flow of time from the reference of external observation and the person doing it (isn't actual FTL velocity causing backwards time?). But in a "warp bubble" for lack of a...
34. ### Acceleration in a space time diagram

I was trying to draw a space-time diagram representing two objects traveling through spacetime, me and the planet Earth. At first I thought I would just draw two straight lines heading upwards some distance, x, apart, seeing as my position relative to the center of the Earth would not be...
35. ### Bending space and space time - what is the difference?

Sorry... This question may be very basic. As a self taught, I understand that the mass will bend the space around it such that any other mass entering the bent space will immediately be pushed towards the center because of the bent space. Higher the mass, higher will be the bent (if that is the...
36. ### What causes magnetic repulsion and attraction?

is magnetic repulsion and attraction is due to the bending of curvature of spacetime?
37. ### Twin Paradox - Question on Space Time Diagram Analysis Resolution

I started a thread previously (https://www.physicsforums.com/threads/time-dilation-happens-on-moving-frame-but-which-one.814622/) around this concept but it got closed by one of the staff after helpfully pointing me to...
38. ### NASA Interest thread: Nasa warps space time

Not kidding http://mysteriousuniverse.org/2015/04/nasa-may-have-accidentally-developed-a-warp-drive/ Astounding, is it true?
39. ### Quantized Spacetime and Zeno's Paradox: A Solution to the Arrow Paradox?

I was reading about zeno's paradox (arrow), Is it like Quantized Spacetime? that we just move from one 'NOW' to the next? Does zeno paradox can be fully solved?
40. ### Did space time be created at the Big Bang?

Did space time be created at the Big Bang, if it did, then theoretically, gravity would not be a fundamental force associated with the Big Bang and any events before the Big Bang would be undefined?
41. ### Perception of time, relative and distant.

Hello! This is my first post, so I should make a small introduction. I am not a science expert in anyway shape or form, but I am a keen enthusiast who regularly keeps up to date with science news through popular websites such as IFLS, Space, BBC etc. I have been wondering about this particular...
42. ### Curvature of Space-Time: Why is Covariant Derivative Nonzero?

I recently watched Susskind video on general relativity. I am unsure why the commutator of the covariant derivative of the vectors is nonzero when there is curvature. E.g. DrDsVm-DsDrVm In flat space, that difference is zero. But why is it non zero in curved space? Someone please enlightened...
43. ### The modelling of space time through Riemann tensor calculus

How do we explains space-time through Riemann Calculus?
44. ### Why does mass affect space time?

A large body like the Earth warps space time in its vicinity. This explains the appearance of gravity from the body. But why does a mass bend space time? What is the connection. What is the thing that mass has that makes space time want to warp around it? There must be some communication...
45. ### Question about Gravity and curvature of space time

Hello all I just joined this forum so forgive me for jumping right in but I have a question about Gravity and the curvature of space time that I can't get answer with a Google search. My question: though I understand that an object remains in orbit because of the curvature of space time and it...
46. ### Uncovering the Reality of Space-Time: Separating Fact from Fiction

Is Space time having a actual reality or is it just a mathematical concept to calculate the coordinates of a point in space?
47. ### Can light exist without space time?

Since the medium in which light propagates is space time, would light be able to exist if spacetime did not exist? Is this like one of those chicken/egg problems, or can light be thought of as a legitimately independent entity?
48. ### Space-Time Vibs: Moving Objs Effects & Cycle

Does both space & time vibrate when objects move or when they vibrate when objects accelerate? So, what happens of these vibrations? How are they converted back into matter to maintain a cycle?Do these vibrations affect the motion of other moving objects (although negligible)?
49. ### (Relativity) Space Time Interval

Homework Statement Frames S and S' are moving relative to each other along the x and x' axes. They set their clocks to t = t'=0 when their origins coincide. In frame S, Event A occurs at xA = 1 yr and tA = 1 yr, while event B occurs at xB = 2 yr and tB = 0.5 yr. These events occur...
50. ### Why do the space time get curved around a massive object?

As far as I have the knowledge of GTR that a mass bends the space time around it.But why does this bend occur?The example from real life that when a mass is placed on a net then the net bends but it us very difficult for me to visualise the situation of bending of spacetime due to a mass.What is...