A 4th Dimension...

If you still need help on this question, we live in a 3-dimensional universe, with three sets of directions. Up/down, left/right, forward/backward.

You'd better get this answer right, or whatever appears in the afterlife will punish you, making you say "Uncle Peter!" repeatedly.

We do actually know of four dimensions already, and the fourth dimension is time. But what about extra space dimensions?

The possibility of there being more than three dimensions was first suggested by Polish mathematician Theodor Kaluza and Swedish physicist Oskar Klein in 1919. According to their theories, there could be an arbitrary number of additional space dimensions present in our three-dimensional universe, the catch would be that each and every one of these dimensions would be present in every part of the universe, but rolled up (as opposed to the regular three dimensions which are stretched out) in every spot. This theory seems very odd indeed, and as the rolled-up spaces would be about one Planck length big if they did exist, there's no way we could prove that they exist through observation. So why assume that they do exist?

This was during Einstein's great days, and Kaluza picked up the theory of relativity to try with four-dimensional space. Kaluza took Einstein's equations, added one dimension, and derived them. What did he find? The answer is rather shocking - he had discovered that his equations for relativity in four-dimensional space were equal to the equations Maxwell had presented in the 1880's for the electromagnetic force. And what did this mean? Kaluza had found that gravity and electromagnetic force (light) were essentially related. Prior to this point, they were assumed not to have anything in common.

Kaluza sent his work to Einstein, who at first seemed interested but soon wrote back saying that he didn't find it very convincing. Two years later, Einstein did however change his mind and decided to acknowledge Kaluza's work. Unfortunately, Kaluza's theory didn't appear to work very well in experiments, so it was put away so to say. But things were to change. In the 1980's, the supersymmetric string theory, or superstring theory, was invented. Superstring theory not only allowed extra space dimensions, but also actually required them. In fact, superstring theory set the assertion that there must be nine or even ten space dimensions!

Is superstring theory correct? We don't know. Superstrings are so small that phycists of today don't know how it'd be possible to observe them. However, most things indicate that superstring theory is correct (unless you're a pessimist), because of its ability to combine relativity and quantum mechanics. If it is correct, then there are up to eleven dimensions with time included.

There is no evidence whatsoever for the existence of additional dimensions. No experiment has been able to prove that any such dimensions exist. There is however no mathematical evidence that they don't exist - I personally believe that the fact that the mathematics of superstring theory involving more than three space dimensions works out as well as it does (well, there are equations which have never been solved by humans, but whatever) suggests that it isn't complete crap.

Bear in mind that graviton, similarly to extra dimensions, has never been observed because it's extremely small and has extremely little energy. Still, the graviton just has to exist (unless a new exotic explanation model pops up which revolutionizes our view of the world of sub-atomic particles).

I do believe that there are more than three dimensions of space. There are those who don't. Can four-dimensional space be imagined by humans? I don't know. We perceive the world by intuition, and no (normal) human has the intuition to understand four-dimensional space. But as four-dimensional space can be expressed mathematically, I can't find any logical reason why it would be impossible for a human to understand/imagine it.

Calabi-Yau-spaces at around 6 or 7 dimensions are pretty sexy.

To read: The Elegant Universe: Superstrings, Hidden Dimensions and the Quest for the Ultimate Theory by Brian Greene.

Time.

I think that describing the 4th dimension as "time" is really a cop-out of the debate, as the very definition of dimensions as we know them are identical evenly perpendicular planes of direction. Time is not a plane of direction. It is something else altogether.

Imagine a 2-dimensional universe where everything was flat. People could see flat images like drawings ef cubes and other inherent 3D illusions, they just wouldn't recognize them as 3-dimensional.

I think that this existence is the same. We see 4D projections all the time, our brain just isn't fooled into thinking it's 4D the way our brain is fooled into thinking the 2D flat image of Doom on our monitors is 3D.

Here is a 4-dimensional object. Don't forget to use both mouse buttons.

Yeah, time is marginally different from dimensions in space. But it's still a dimension by definition.

whoa, that cube has extra quarters. i saw the tesseract serveral times in class, fascinating stuff.

Extra dimensions? Watch Supernova.

That 4-d cube is interesting, can someone explain just how it works?

Anyone who believes the time dimension is wholly distinct from the three space dimensions should look at the mathematics of a black hole (or indeed within any strong gravitational field).

The question here should really be about a possible 5 (or higher) dimensional spacetime. I'll answer that question with a definite maybe!

Fredrik: I'm not sure the graviton really has to exist. Quantum theory and General Relativity contradict one another in certain ways, so at least one of them might be a false way of looking at things - it works up to a point but needs ultimately to be replaced by a more all-encompassing theory.

BTW, has anyone ever played 4-dimensional (5x5x5x5) or 5-dimensional (6x6x6x6x6) noughts and crosses (tic-tac-toe)?

Fredrik: I'm not sure the graviton really has to exist. Quantum theory and General Relativity contradict one another in certain ways, so at least one of them might be a false way of looking at things - it works up to a point but needs ultimately to be replaced by a more all-encompassing theory.

The fine thing about superstring theory is that it is able to combine both theories at the extremes where they usually begin to contradict each other.

The graviton doesn't have to exist. I'm not sure that we'll ever be able to prove that it exists as it'd require a particle accelerator about the size of a galaxy, roughly. But the graviton provides a simple a model of explanation that is uniform with other concepts and possibly allows deriving it to the same fundamental force that makes up the weak & strong + electromagnetic forces. (Correct me if I'm wrong, it's a fair while since I read about this).

Time is not a fourth dimenstion, thats a total cop out because YOU CAN HAVE TIME IN TWO DIMENSIONS. Of all people doom players know this the most, they look at a TWO dimensional surface and things MOVE. DUH.

Time should be considered a zeroth dimension that can apply to whatever, the concept of dimensions was designed for SPACE

Xian said:

Time is not a fourth dimenstion, thats a total cop out because YOU CAN HAVE TIME IN TWO DIMENSIONS. Of all people doom players know this the most, they look at a TWO dimensional surface and things MOVE. DUH.

Time should be considered a zeroth dimension that can apply to whatever, the concept of dimensions was designed for SPACE

You don't have a clue what you're talking about. If there were only two "regular" dimensions, then time would be the third dimensions. It'd work just as well as time does with the three dimensions we're used to.

Why should time be considered a zeroth dimension? We start counting from one.

Time doesn't have some unique property that it "applies to whatever" in some arbitrary way - all dimensions have exactly the same properties. The difference is that time as we know it usually is linear.

Like Grazza said, try doing some calculations with complex physical situations and you'll discover that time and space are essentially identical.

If you know anything about Einstein's theory of relativity, then you should know that it requires that time and space are a "union" and not separate things that apply to each other differently. And Einstein's theory of relativity is as far as we know quite right.

Absolutley none of the facts you stated conflict with what i just said

Time should be a zeroeth dimension because you can have time in One dimension (the scalar as something falls for an example- positive number to negative number) Or Two dimensions (For example a game of tetris) or Three dimensions (Life as we know it). Theres no reason to "add it on" because as you said, it something that is PART of a dimension.

So if wee use your definition, computer games are three dimensional because they move, and real life is fourdimensional becasue theres a z-axis, obviously wrong

Time is not relevant as it is distinctly different from the three dimensions. The question is if it is possible for a realm to be distinctly 4-dimensional, and you can add time as the 5th dimension if you want. Saying "Time." as a reply is the same as saying "Durr huh?"

Whether time is comparitive to the dimensions is irrelevent, time is NOT the kind of dimension we're talking about and you're copping out by suggesting "time."

Fredrik said:

Lots of stuff.

To read: The Elegant Universe: Superstrings, Hidden Dimensions and the Quest for the Ultimate Theory by Brian Greene.

You are SMARTER THAN ME!!...or at least more knowledgeable..Kudos to you! (not that i'm really smart, if it sounds that way)

Xian said:

Absolutley none of the facts you stated conflict with what i just said

Time should be a zeroeth dimension because you can have time in One dimension (the scalar as something falls for an example- positive number to negative number) Or Two dimensions (For example a game of tetris) or Three dimensions (Life as we know it). Theres no reason to "add it on" because as you said, it something that is PART of a dimension.

So if wee use your definition, computer games are three dimensional because they move, and real life is fourdimensional becasue theres a z-axis, obviously wrong

Think of it this way, on a flat plane things span out in the X-direction, (horizontal)
Things span out in the Y-direction, (vertical) but things also have depth (3rd dimension)...time is like that just as something becomes 3 as you define it's depth, something spans forward through time, though we can't see it this way, because we move with it, if we could remain static, it would be like watching something with a strobe light, it's position determined by it's place in time, and ever-changing, dunno if that sounds like a good explanation.I was attempting to simplify a complex subject.
Sorry fredrik, i am not thee.

Xanthier said:

Think of it this way, on a flat plane things span out in the X-direction, (horizontal)
Things span out in the Y-direction, (vertical) but things also have depth (3rd dimension)...time is like that just as something becomes 3 as you define it's depth, something spans forward through time, though we can't see it this way, because we move with it, if we could remain static, it would be like watching something with a strobe light, it's position determined by it's place in time, and ever-changing, dunno if that sounds like a good explanation.I was attempting to simplify a complex subject.
Sorry fredrik, i am not thee.

but why in that order? woudltn it make sense to put time at the BEGINING and not the end? How do we know that our third dimesnion is the last one and that time comes AFTER it?

AndrewB, are you talking to me or Sphagne? Because I think I quite clearly made my statements about dimensions of space :)

Xian said:

but why in that order? woudltn it make sense to put time at the BEGINING and not the end? How do we know that our third dimesnion is the last one and that time comes AFTER it?

There's no point in arranging the dimensions like that. We can't say that X is the first, Y is the second, etc, because the 'X' and 'Y' can't be defined as absolute directions (the concept of ether was abandoned 100 years ago).

Maybe you're right, it would make sense to refer to time as dimension zero or one, but it really doesn't matter.

And Xanthier said:

Sorry fredrik, i am not thee.

Hey dude, I don't understand much of this either. I only know some of the abstracts.

It is the 4th dimension simply because it was "discovered" and added last. It is just a name, a number for a list. You can't even say the dimensions are spacial unless you consider them all from our perspective and in relation. Time quite is as "spacial" as a line, a dot, or the "volume" of something unless you live in the 12th century.

The ordering of the four dimensions is arbitrary. In GR the standard convention is to put time first (in tensor notation and stuff).

Black holes: the solution of the Einstein field equations within a black hole involves substituting the time coordinate with one that also depends on the space-like coordinates. Show me a solution that doesn't do that, and I might start to believe that time can really be separated from the three space-like dimensions.

Fredrik said:

The fine thing about superstring theory is that it is able to combine both theories at the extremes where they usually begin to contradict each other.

It's quite a few years since I studied any of this stuff (I was at Cambridge 1986-9). I'm aware of superstring theory being discussed as a promising-looking way forward, but don't know how much progress has been made. Likewise the "foam" theory that was intended to tackle the first 10^-43s of the universe.

Fredrik said:

But the graviton provides a simple a model of explanation that is uniform with other concepts and possibly allows deriving it to the same fundamental force that makes up the weak & strong + electromagnetic forces. (Correct me if I'm wrong, it's a fair while since I read about this).

It would be neat, logical, elegant and consistent for gravitons to exist. I'm just saying that the theories that lead one to think that might well require some revision.

AndrewB said:

I think that describing the 4th dimension as "time" is really a cop-out of the debate, as the very definition of dimensions as we know them are identical evenly perpendicular planes of direction. Time is not a plane of direction. It is something else altogether.

No, we just perceive it that way.

I think I'm blind.

Ct_red_pants said:

I think I'm blind.

Heh.

I think I am brain dead reading replies to this thread. Or any other thread concerning the universe/dimensions/physics...cause all everyone does is BLAH this and FUCK that...

EVERYONE HAS THEIR OWN OPINION GET USED TOO IT...

The universe exists. Time is here. Wow.

There are about unlimited number of directions and dimensions in this world, for instance:

Dimention connecting here and there.
Yesterday and tomorrow.
Coldness and hotness.
Darkness and lighness.
Badness and goodness.
Cowardiness and bravery.
Weekness and strongness.
Sameness and difference.
Yellowness and redness...

There is another sort of directions that are above normal ones, and those are the ones that connect sources to effects like.

Direction between "Human being" and "Individual humans"
Wood and wooden things.
Goodness and good people.
One to thousands.

Sorry, it just blurted out. ;-)

Time is a cultural artifact. A variable in equations. Useful for plotting the movement of an object through any one of the three dimensions in real space or on graph paper.

AndrewB is right on the money on this one. That 4D model is facinating.

What I said above is that the other three dimensions are also like that: A variable in equations. Useful for plotting the movement of an object through any one of the three dimensions in real space or on graph paper, inextricalby bound to any one or all of the three dimensions. Unless you speak in classical, absolute terms. But that isn't scientifically meaningful. But then again that is, I assume, what AndrewB is looking for in this poll/thread.

Does anyone truly understand how 4-D works? Everyone understands 1-d (line) 2-D (flat image) and 3-d (depth)

No. It takes an extremely powerful and twisted mind to picture a 4D object. Our minds are not designed to be able to even imagine it. We have to pretend to imagine it, really.

Actually, a hypercube (a four-dimensional cube) isn't that hard to picture, if you've seen one.

Our current notion of time is a little skewed. The human mind recieves far too much information, so it has to order it (we recieve information from the world in much the same way that a teacup recieves water from a firehose). That ordering gives us a sense of time. That's part of why Alzheimer's makes people relive old experiences. The physical makeup of their brain changes, and with it their ability to order time. That sort of effect can actually be done without changing brain chemistry (Vietnam vets, for example), but that's really more of a stress thing than an age thing.

I firmly believe that Time, as the 4th dimension, exists. I also firmly believe that I am wrong. That's really the only way I can possibly remain sane enough to look at a clock.

DC