How does spacetime work?
830585
Y'know, I've been trying to get a handle on that for a long time, but so far I understand it to mean that post-Einstein, once you  include time as a fourth axis to the 3 spatial ones, the universe makes sense in terms of our physical laws working everywhere and everytime.  That is a neccessity of a good physical law - it must always work no matter where in the universe you test it or how fast you're travelling.  In other words, translations and rotations of objects or fields or whatever must have no effect on the validity of the law.  If you do not include time as an axis perpendicular to the 3 spatial ones (mathematically, of couse), what we predict won't agree with what we see, especially in such cases as high relative velocities (as in approacing the speed of light), and strong gravitational fields.  Amoung the oddest result of this view is that, in truth, all time actually exists simultaneously, and there is some not-quite-understood mechanism that only lets us see one instant at a time.\n\nAnyway, to answer your question, "How does spacetime work?", the answer is, much better than space or time alone and separate.  They are, in fact, as inseparable as the pair of poles of a magnet.\n\nThis all might be not quite accurate, especially since I'm so far just an "armchair physicist" with no formal education in the area, (tho I'm looking forward to taking physics, including the higher levels, if I can ever get thru these friggin' calculus classes).  Anybody else have something to contribute or set me straight on??
314377
Masses with large gravitational field bend space all the time. Light traveling towards a star bends at close proximity and strengthens out when its farther away.\n\nBlack holes are said to hold immense gravitational field that not only does it bend space and time, it can also rip a hole through our 4-dimensioned universe.
257950
There is nothing called 'spacetime'\nIt is scientifically named space-time.\nIt means ***central concept in the theory of relativity that replaces the earlier concepts of space and time as separate absolute entities. In relativity one cannot uniquely distinguish space and time as elements in descriptions of events. Space and time are joined together in an intimate combination in which time becomes the "fourth dimension."***
1186741
Time is called a dimension because in Einstein's theory of relativity it makes mathematical sense to do so. Events happen in spacetime, 3 spatial and 1 time dimension. But their orientation in space and time relative to each other, depends on the observer and the relative speeds of the events.\n\nIn Einstein's formulas these dimensions are mixed by transformations depending on the velocities. This works only if we add time as a dimension.    \n\nTo give the *position* of an event in four dimensional space-time you need to give a reference observer first, another event, relative to which you measure.  And the answer will depend on your speed and the speed of the observer. And that is just what relativity means: the resulting coordinates or not the same for everybody but depend on the relative speeds.
678785
The basic idea behind space-time comes from Einstein’s General Theory of Relativity, so if you’ll bear with me for a moment… What he proposed was a totally new, geometrical description of space and time that led to a different description of gravity—one that linked space to time and mass to energy in a fundamentally geometrical fashion. In other words, mass(-energy) shapes space(-time) instead of acting like a “force” in the traditional Newtonian sense. This alteration in the fundamental geometry of space-time is often described as the “curvature” or “bending” of space. \n\n(Thus, in Newton’s description of gravity, one would say that all bodies exert an attractive gravitational force on one another; “space” is just the place where it happens. In Einstein’s conception, one would say that all bodies change the underlying geometry of space—and time, too—in a way that causes them to be attracted to one another.)\n\nWhat’s important to note is that, in Einstein’s conception, space and time are linked together in a way that doesn’t allow the two to be considered separately.  So we often talk of space-time being “warped” or “curved” by the presence of mass(-energy). The only we see space-time deformed in the Universe around us is by the presence of a lot of matter—light being bent around the Sun, clocks being affected by Earth’s gravity, that sort of thing.  \n\nThe caveat I feel compelled to add is that curvature or bending really only provides an analogy to what the equations tell us. If you want to imagine the effects of an object on its surrounding space(-time), then you can think of it as changing the shape of space(-time) in its vicinity. The distortion is real—we can measure its effects—but the images that are often presented (of flexible sheets of space-time with bowling balls or marbles rolling around on them) simply present analogous situations.\n\nI guess that’s a lot more than you asked for.  I hope it helps.\n\n\nRyan Wyatt\nRose Center for Earth & Space\nNew York, New York
1101873
First I will address your difficulty with the answer someone gave to your earlier question.\n\nSpace is expanding between distant parts of the universe, and presumably very slowly on local scales too (~100 km/s per MPC, works out to about 100 nm/s over a distance of a meter.  Hmmm, I wonder if one could devise an experiment to measure that. . . )  \n\nLocally, things like gravity (in the case of a galaxy) or electromagnetic forces (in the case of a less than planet sized solid) overcome that expansion. If everything in space was expanding uniformly, we would never notice that phenomenon, because the "rulers" we use to measure distance and size would be expanding too! \n\nSo, you can throw your baseball, and maybe space will expand between the two of you as it travels, however the friction between the two of you and the ground, and the chemical bonds and electrostatic forces in the strip of ground between you and your dad do not permit the two of you to be dragged apart by the expansion of space during the ball's travel time, just as those same forces prevent your body from expanding with the expansion of space.\n\nThe answerer was incorrect in their generalization. I will take a look at this earlier question you asked; in context the part of the answer might be OK, but it appears to be too general a statement the way you presented it.\n\nKeep questioning answers;  you have the makings of a good scientist, philosopher, lawyer or other combination creative and analytical  endeavour.\n\nYour more general question was about movement in "space-time." If you define movement by a change in space-time interval, then the difficulty is in staying still!  In fact, you have to move through 3-D space at the speed of light to experience zero change in the space-time interval between two events; only light itself is frozen in space-time in those terms.\n\nWiki has a good section on space-time intervals:\nhttp://en.wikipedia.org/wiki/Space-time_interval#Basic_concepts
933949
Theory of relativity.
396914
Outer space is not nothing. Even without the presence of matter, it is teeming with quantum foam, particle-antiparticle pairs, space, and time. For all we know, spacetime may not exist outside our universe."\nAlso, the universe may not be bounded. The only way to "exit" may be to find a "fourth direction". Ie., think of a point in an unbounded plane. The only way for the point to exit its universe is to somehow find the "third direction".
514555
Space consists of nothing!\n\nSpace is mostly empty, with a spattering of matter in the form of galaxies, which are drifting further and further away from each other as time moves in the +ve direction.\n\nMatter and energy are mutually convertible.\n\nTime is the fourth dimension, and an important function of entropy or the running down of things.\n\nAs time moves in the +ve direction i.e. forward, entropy increases, things get run down and the energy dissipates over the expanding universe, as does matter, that means that as time goes by, the average density of the universe as we know it reduces, the matter-energy per unit area also reduces.\n\nAs time moves backward, entropy reduces, the space reduces to a point and matter and anti-matter coalesce to nothingness.\n\nst
598318
The basic idea behind “folding” space or time comes from Einstein’s General theory of Relativity, so if you’ll bear with me for a moment…  What he proposed was a totally new, geometrical description of space and time that led to a different description of gravity—one that linked space to time and mass to energy in a fundamentally geometrical fashion. In other words, mass(-energy) shapes space(-time) instead of acting like a “force” in the traditional Newtownian sense. This alteration in the fundamental geometry of space-time is often described as the “curvature” or “bending” of space. \n\n(Thus, in Newton’s description of gravity, one would say that all bodies exert an attractive gravitational force on one another; “space” is just the place where it happens. In Einstein’s conception, one would say that all bodies change the underlying geometry of space—and time, too—in a way that causes them to be attracted to one another.)\n\nSo we often talk of space-time being “warped” or “curved” (honestly, “folded” sounds a little extreme) by the presence of mass(-energy). The only we see space-time deformed in the Universe around us is by the presence of a lot of matter—light being bent around the Sun, clocks being affected by Earth’s gravity, that sort of thing.  To do something similar (like the “Smallville” example) would require very large quantities of mass or energy.\n\nThe caveat is that curvature or bending really only provides an analogy to what the equations tell us. If you want to imagine the effects of an object on its surrouning space(-time), then you can think of it as changing the shape of space(-time) in its vicinity. The distortion is real—we can measure its effects—but the images that are often presented (of flexible sheets of space-time with bowling balls or marbles rolling around on them) simply present analogous situations.\n\nThe issue with “folding” is that it suggests something like a crease in space-time, and that’s problematic in the sense that gentle “curves” or “warps” are mathematically simple to describe, but adding anything like a hard edge becomes tricky.  Plus, to make the transition from one part of space-time to another requires bringing those two points in contact—a challenge that makes “folding” look simple!\n\nJ. Richard Gott wrote a book, “Time Travel in Einstein’s Universe: The Physical Possibilities of Travel Through Time” that addresses the “reality” of time travel from the perspective of contemporary physics:\nhttp://www.powells.com/partner/30700/biblio/0395955637\n\n\nRyan Wyatt\nRose Center for Earth & Space\nNew York, New York
179736
It depends on how you look at it as to whether gravity bends spacetime, or gravity attracts light, which in turn is experienced as a "bend" in something we like to call "spacetime".  \n\nPersonally, I look at it the second way, and I think there are a lot of good reasons to do so. \n\nOne, you can derive the space and time distortions of special relativity caused by speed simply by considering what light behaves like as things approach the speed of light given that light must remain at the same speed regardless of the observer's frame of reference.  The need for the speed remaining constant regardless of observer's speed both makes common sense and can be concluded from Maxwell's equations.  \n\nCommon sense?  Yes.  Consider the following thought experiment:  Take a large sphere, like a planet, with clocks placed evenly around the equator.  Observe it from a moderate distance.  Since this is a thought experiment we can make the rules whatever we want.  First, we'll assume that light speed can vary, and that simple Gallilean transforms, in which speeds are additive, are in effect.  Second, let's make the sphere out of "unobtanium": a metal so strong that it's indestructible and cannot be deformed by any force. \n\nStart spinning the sphere.  Since simple Gallilean transforms are in effect, light coming off the center of the sphere, directly in front of you, will reach you at the speed of light, light coming off the receeding limb will be slowed by an amount equal to the speed of the sphere's surface, and likewise light on the approaching limb will be sped up.  As the sphere spins faster and faster, interesting things will happen.  One, the clocks on the approaching limb will move into the future, while the receeding limb will move into the past, and clocks right on the centerline will read your time, minus the time of flight for light.  If you follow a single clock, it'll oscillate between the past and the future as it goes around, and any actions observed on the surface will be similarly disordered.  From your perspective causality totally breaks down.  At the speed of light, the receeding limb will disappear entirely, and not only will things be moving from the future into the past, but they'll be blinking in and out of existence.  Of course, if you were on the surface, everything would seem normal, but an observer who is stationary relative to the surface will see both time and space breakdown.  So, clearly we need some mechanism to allow for information to move from the surface to a stationary observer in a way that preserves both causality and existence if we're to have a cohesive universe.  This solution can be made using the Lorentz transfroms.  Time and space distort, but existence and causality are retained.  It's better to have a wiggly but coherent spacetime than a discontinuous and broken one, so Lorentz tansforms, and the uniformity of the speed of light from all reference frames, is the way to go.\n\nIf you generalize from there with the observation that gravity is indistinguishable from a physical acceleration, you end up with the full implementation of general relativity.  \n\nSo, notice something about model of why relativity is needed to maintain continuity of spacetime: it's all about light transfer.  \n\nIf you think about it, exchange of light is the only way you know anything is there, and time is way of looking at the changes in what is there.  In other words, it's not the bends in spacetime that make light bend, it's the bending of light that makes spacetime bent.  \n\nLight is the primary carrier of information in the universe, and in order to have a cohesive body of spacetime which can be called a universe, this information needs to be carried uniformly so that any given point can be informed by what goes on around it, thus the invariability of the speed of light.  \n\nSo, you can consider that light, although lacking
894018
Time is called a dimension because in Einstein's theory of relativity it makes mathematical sense to do so. Events happen in spacetime, 3 spatial and 1 time dimension. But their orientation in space and time relative to each other, depends on the observer and the relative speeds of the events.\n\nIn Einstein's formulas these dimensions are mixed by transformations depending on the velocities. This works only if we add time as a dimension.    \n\nWill we ever be able to travel to time? Well, weird things happen to the equations close to black holes and their mathematical opposites, white holes. So who knows?\n\nBut I don't think so... suppose sometime in the future time travel will be  invented. Wouldn't we see these travellers once in a while?
334764
general relativity includes special relativity, but is mostly about how gravity works and large objects warp spacetime, causing other objects to come near them. special relativity deals with the effects of moving really fast, and how light travels at the same speed relative to any observer, so observers at different speeds will disagree on length, time and mass of things they observe.\n\ngeneral - about big stuff\nspecial - about fast stuff
1139481
It is the results of Einsteins work on relativity. Einsteins showed gravity cause space-time to warp which will affect how objects interact with each other. Newton explained gravity as the attraction one object has for another, Einsteins theory's have made up for some of newton's short falls, such as Mercury's orbit which doesn't stay the same each time changes with each orbit. Newton laws don't account for this change but Einsteins theory's predict these changes exactly. Theory's of Space-Time were never design to explain the Ether.
768008
Hi,\n\nFirst think about space as a big sheet of saran wrap. Then imagine that mass distorts the sheet, causing wells, or dents in it. now imagine that the photons need to travel along the saran wrap (i.e. traveling through space) and it makes sense that they would seem to change directions with respect to gravity. \n\nThat is a gross oversimplification, but I think that the analogy is roughly correct.\n\nHope that helps, \nMatt
437322
The mathematics of black holes shows that they might be able to transport you to another region of space or possibly another universe. However, the mathematics also shows that the connection only lasts for a fraction of a second at a time, and that the link to other universes depends on a specific set of conditions which scientists do not believe to exist. Even if it were likely, however, the strong gravity field of the black hole tears apart any material falling into the hole so it would not come out the other end of the Black Hole looking anything like how it went in, so in other words you would  have to really want to make this discovery because you’re going to die trying.
1110928
Einstein explained gravity as a warp in the time-space continuum.  The best explanation I've ever seen was at a museum.  It's hard to explain with words, but imagine a square piece of fabric stretched taut on all 4 edges.  Now, place a weight (a ball, say, to represent a planet) in the center of that fabric.  It causes the fabric to stretch, and distort.  And any small items (marbles, say) that get in the area near the ball will roll toward the ball.