Why is time the 4th dimension?
494471
Kemmy's answer is actually a very good answer.  It seems simple, but it's quite insightful.  Time is referred to as a 4th dimension (along with the three spatial dimensions) because you when you represent physical situations using geometric coordinates (x,y,z,t), you can treat time 't' in the same way as you treat the spatial coordinates x,y and z.  In fact, many physical laws such as special relativity are significantly simplified if you treat time in the same way as the spatial dimensions.\n\nHowever time is obviously very different in some ways:\n\n1. Units are different (seconds instead of meters, feet, cm)\n2. You can only move in one direction along the time axis, whereas you can move backwards and forwards along the spatial dimensions.\n3. Entropy (disorder) increases only increases with time, but seems to have no relationship with space.
90606
I believe that space and time are just 4 of the 11 dimensions that the strings exist in, and vibrate in, giving rise to the particles and their properties as we know them.
16531
Three dimensions define space.  Time is the fourth dimension.  This is the reason for using phrases like space-time continuum.  One might say that time co-exists with space, not in space.  (By space I assume that you mean the volumes between the stars, but this is no so different from the space here on Earth).\n\nBlack holes are another matter (literally).  Mass and velocity effect both time and space.  The greater the mass, the larger the effect.  A location known as a black hole has a mass so large that space is bent into a gravity well.  As one approaches the outer limit of the black hole (to the point of no return, called the event horizon), one would find an increase in velocity due to the gravity well.  At the event horizon, for all practical sense of reality, the universe as we know it stops.  Beyond the event horizon, no material object, nothing, not even light can escape.  As velocity increases, space would appear to compress along the direction of motion and time would appear to slow down to an outside observer, but the outside observer could observe anything beyond the event horizon (no light coming out, remember?).\n\nIf this is not clear enough shoot another question.
72098
Some new ideas in physics posit that there are more than the obvious 3 spatial and 1 temporal dimension. These theories are intended to explain all four fundamental forces in nature (electromagnetism, the strong nuclear force, weak nuclear force and gravity) by serving as a bridge between quantum mechanics and general relativity.\n\nIt turns out that one way that - perhaps - QM and GR can be connected is to postulate some extra dimensions, with an extra 7 spatial dimensions for a total of 11. If such extra dimensions exist they may be too small to interact with our standard 3D+time word.\n\nSo, in this case, a 6th dimension would be one of these smaller extra dimensions.\n\nIt should be noted, though, that thus far string theories are very theoretical, and there is no real physical evidence (yet), nor even a complete theory. Its still very much up in the air.\n\nA nice, simple guide to string theory basics can be found here:
187814
The 4th dimension is time and the 5th dimension is quantum probability, where every possibility occurs in an infinite number of "parallel universes."
255954
I will take a shot at it.\n\nWe are all very familiar with 3 dimensional space, up down, left right, forward backward. To describe the location of an object in space we have to use those three dimensions. BUT. Nothing is actually fixed in space. Everything is moving. So in order to describe the location of an object in space you must also describe at what time that object was at that location or will be at that location. That is why time is called the 4th dimension. \n\nNow here is the really bizaar part. Some scientists think there are more than 4 dimensions. Some propose 10 dimensions and some 26 dimensions. It is called string theory and it is all over my head.
1012182
A four-dimensional hypercube.   If you consider time as a fourth dimension, a tesseract would be a cube which has sides of, say 1 metre, suddenly appears, exists for the time equivalent of 1 metre, that's the time it takes light to travel 1 metre, which is 1/ 300 000 000  second,then vanishes.
355582
As a previous poster mentioned... time is the fourth dimension.  You can easily visualize this when you imagine an object moving in three dimensional space.  The movement represents the fourth dimension.\n\nI think you are asking about a fifth dimension.\n\nPeople have mathematical models for up to eleven dimensions.  I suppose that a person who knew the mathematical models for these dimensions could imagine them visually.
886
Classical physics theories describe three physical dimensions: from a particular point in space, the basic directions in which we can move are up/down, left/right, and forward/backward. Movement in any other direction can be expressed in terms of just these three.\n\nTime is often referred to as the "fourth dimension". It is, in essence, one way to measure physical change. It is perceived differently from the three spatial dimensions in that there is only one of it, and that movement seems to occur at a fixed rate and in one direction. The equations used by physics to model reality often do not treat time in the same way that humans perceive it.\n\nTheories such as string theory predict that the space we live in has in fact many more dimensions (frequently 10, 11 or 26), but that the universe measured along these additional dimensions is subatomic in size. As a result, we perceive only the three spatial dimensions that have macroscopic size.
527767
Without the fourth dimension, no three-dimensional object would exist.  So the simple answer to your question is YES.\n\nThe more complicated one is SOMEWHAT.\n\nThere is no true stationary object in the universe that we know of.  Even an atom held at absolute zero still has velocity in that the medium it's being held in is still moving along with the rest of the earth, solar system, galaxy, etc.  Anything that moves through space is also moving through time.  So, without time (widely regarded as the fourth dimension), no motion would be possible.\n\nIf no motion were possible, then the ability to measure and quantify that three-dimensional object would also be impossible, and thus the whole question becomes paradoxical and irrelevant.\n\nConfused yet?  I am... :)
44234
Well there are lots of things I do not completely understand about the structure of the universe. \n\nFor example, some current theories are that our 4 dimensional space-time continuum is just part of a higher dimensional entity, where some of the other dimensions are rolled up. However, the time dimension of our 4 dimensional environment is clearly much different than the spatial dimensions, since we appear to only be able to travel in one direction along the time dimension, although many of the equations capturing the physical laws of our universe are invariant when we replace time with -time.\n\nThe expansion that people refer to when they say that the universe is expanding refers to the entire 4 dimensional space-time continuum and possibly some  of the other dimensions as well. This gets very hard to visualize. What I do is think of us as ants living on the surface of a balloon that is being slowly inflated, so the dimensions of the balloon are increasing, and distant parts of the ant's space are becoming increasingly distant. However, this is probably a very limited analogy. \n\nTo get a better picture, you need to consult someone who has thought very hard and very carefully about what the universe is, or supposedly is.
471213
It all dependend where you are filling time. In an insane intitution there are people who experience 4 ,5 of more dimentions . so far I have heard of 26 dimensions being filled including many dimentions of time.\nSpace and time have the same thing in common they can be filled both at the same instance!
808556
Two views on the space and time.\n1.\n There are an independent space and independent time:\nWe notice it on our planet - Earth.\nIt is a fhree - dimensional space.\n2.\nThere is simultaneous union of space and time:\nIt is negative four-dimensional (Minkowski) space.\nHerman Minkowski :\n“ Henceforth, space by itself, and time by itself, \nare doomed to fade away into mere shadows,\n and only a kind of union of the two will preserve an independent reality.”\nQuestion.\nWhat  is the “a kind of union of the two “?\nThe answer.\nIt is Vacuum. T=0K.\n=========================\nhttp://www.socratus.com
1044107
None.  That is the point.  If they exist is not proved, and hypothetical tests to see if they exist are flawed.  \n\nOn your other question of visualizing multiple dimensions, I have a few hints.  Have you read Flatland yet?  Start there, its good, and not overly mathematical.  Multiple dimensions can mean different things to different scientists.  We use them all the time for their mathematical properties.  But mathematics is just a description, the real world is something observable.  In terms of observation, you would not be able to detect a separate dimension by any means pedantic.  We may be able to prove that physical space has more than three dimensions, but that does not mean that those other dimensions are physical space.  Just like time.  Some particle interactions appear to go backward in time briefly.  What if there is more than one time dimension?  \n\nSo the classic three dimensional physical picture of multiple dimensions will always be flawed by the observers expectation of the properties of the unseen dimension.  Which is why we describe those dimensions using 'imaginary' constructions.  Hope this helps a bit.
706278
I know four dimensions: x, y, z\ntime is the fourth\n\nBut in addition, theories such as string theory predict that the space we live in has in fact 11 dimensions, but that the universe measured along these additional dimensions is subatomic in size. As a result, we perceive only the three spatial dimensions that have macroscopic size
991771
We observe four dimensions everyday, three spatial and time.\nTime is called a dimension because it makes mathematical sense to do so. \nBut...theories such as string theory predict that the space we live in has in fact many more dimensions (frequently 10, 11 or 26), but that the universe measured along these additional dimensions is subatomic in size. As a result, we perceive only the three spatial dimensions that have macroscopic size.\n\nThis is not so strange as it sounds, which I'll show with an example. Imagine you are in an airplane, flying over sea. Seen from a height, the sea looks flat, two-dimensional. But when the plane looses height we start to perceive the waves, that move in a third direction we could see before.\n\nThe universe could be the same. Four macroscopic dimensions and a few more, hidden ones. We can only perceive them for instance, by the small effects their existence might have on subatomic particles.
569838
Time is a forth dimension.