# Who said the fourth Dimension has to be time?

1. Apr 3, 2013

### Gacha

Good Day!

First of all, I'm not an actual physicist so please don't laugh if the following sounds really stupid to you or I don't use the correct terminology. I don't/didn't even study anything remotely related to physics, everything is plainly based on private interest. (The reason I'm still posting in this sub forum follows)

During my free period from university I came across the 10-Dimension theory because I found it really interesting. Everything about it sounds logically clear to me when I learned/read/heard about it, so is the String Theory.

However! When I made up my own thoughts about how dimensions could be built I already stumbled on the fourth dimension. Who said it had to be duration/time? If it wasn't, wouldn't it completely change the way we look at String Theory and most things similar to it? Is there a logical explanation that I just don't see or it it plainly yet another assumption that is interchangeable?

Last edited: Apr 3, 2013
2. Apr 4, 2013

### FermionXLR8r

Because of Einstein, we often call time the fourth dimension. As you know,Special relativity shows that time behaves surprisingly like the three spatial dimensions. Moreover HG Wells popularised the idea that time was the fourth dimension in his book The Time Machine. Yes, if time wasn't considered to be the fourth dimension, it would change the way we look at String Theory..But so far the special theory of relativity has not been proven to be completely wrong, it infact has been the basis of many modern day theories about the origin of our universe.

3. Apr 4, 2013

### bp_psy

The same person that made spatial dimensions to be ordered as x,y,z and not z,x,y.
Imagine how the universe would be if we had (z,t,y,z) instead of (t ,x,y,z) or (x,y,z,t) all those transformation matrices would go all over the place
.

4. Apr 4, 2013

### HallsofIvy

Why we would be walking on our hands and wearing hats on our feet!:tongue:

Gacha, physicsts study "events"- things that happen at a particular time and point. "Time" is a single numeric value that is one way of distinguishing one "event" from another. That is the definition of "dimension" and why time is a dimension. The fact that we think of it as the "fourth" dimension rather than the first or seventh is, of course, purely arbitrary.

5. Apr 4, 2013

### Gacha

I see, thank you! I now see things way more clearly. However that actually reveals so much instability in our theories and world views if you consider that everything is built upon one or two more or less proven assumptions. So basically if somebody proves some theory wrong (which wouldn't be the first time in science) that would mean all the steps we made after this wrong assumption are most likely false and x amount of time has been lost to find yet another theory we can look towards and build things upon. While all that seems a bit tiring its just as interesting to find those new things which might actually be the solution after all.

6. Apr 4, 2013

### phinds

Modern theories are built on facts / reality / experiments. Thus any flaw in the theory is just going to mean that the theory has to be refined. Possibly drastically refined but probably not tossed.

The best example of this is Newton's "Law" of gravity, which not only isn't really a law it's just flat wrong. BUT ... it works to an enormous degree of accuracy on small scales and is still the basis of civil engineering. General Relativity replaced it but GR reduces to Newton on small scales out to many decimal points and the fact that Newton was wrong does NOT change GR, it just shows that GR is in one sense an extension of Newton to a more general case.

7. Apr 4, 2013

### Gacha

Experiments seem quite hard to come up with for theories like these. We would have to scale them all and then relate, but as your example showed - scaling things can also lead to mistakes. I really like that thought of refining and re-working theories instead of tossing them, but doesn't it slow our thinking in certain ways? If we keep holding on to this one theory we tend to get tunnel vision, it's human nature. It might hinder us from looking outside the box to get a whole new approach on things that might even be closer to the solution right off the bat instead of changing and reworking one theory to make it "kind of" work.

Your example is really interesting, it's quite surprising actually. Hearing, reading and observing all of this really makes me want to get more involved in the entire physics department but it's actually too late to make a turn career-wise. Keeping it as a hobby might be the solution but that's just not the same :p

8. Apr 4, 2013

### phinds

We never keep theories just to be keeping them, we keep them if they jibe exactly with experimental results (to within our ability to measure them).

For example. Richard Feynman was fond of pointing out (and this was maybe 30 years ago) that the experimental verification of Quantum Mechanics has been made to an amount that is the equivalent of measuring the width of the United States, between two defined points, to an accuracy of the width of a human hair. SO ... if Quantum Mechanics is found to have a flaw, it will likely be refined, not tossed, but it would not be kept just for the sake of keeping it, it would be kept because it WORKS in all cases that are known so far.

9. Apr 4, 2013

### Staff: Mentor

What assumptions are you referring to?

10. Apr 4, 2013

### Turion

What ten dimension theory? Sounds like pseudoscience.

11. Apr 4, 2013

### Gacha

Nothing specific, just in general everything we claim to 'know' are based on piled up assumptions. Remove one of the basic ones and the tower crushes

1. As I initially said I'm not a physicist. I probably used the word theory too frivolously here. I didn't mean it as an actual theory like the String theory, just the idea of the existence of ten dimensions.
2. It might sound like 'pseudoscience' but actually I'm just trying to understand things that normally shouldn't be of my business because I found it interesting.

12. Apr 4, 2013

### Crazymechanic

Well the tower doesn't crash in all cases just like in a building if you hit a window the building stands just as if nothing happened but if you break half of the support columns and heat up the rest like in WTC you do get a collapse , a pretty huge one indeed.(yes I know the WTC was a strange structure not only for it's time but in overall but that',s not important here )

the thing i wanted to point out with this is that in every major science theory there are things that can be adjusted and so and there are some basic fundamental facts.
Now the only way how to collapse a theory pretty much completely would be to prove wrong one of the fundamental facts of it.
Just to name an example if someone would prove that light speed isn't constant indeed then we would be in alot of trouble , starting from the SR to the age of the universe to everything else.
Now ofcourse your burger would probably taste just as good as before but then again life is not only about eating and existing.

13. Apr 4, 2013

### Gacha

I agree a hundred percent. On that last note we would actually almost hit the philosophy/religion border. I noticed that quite a lot, it seems to be closer than one would assume at first.

Thank you for explaining these things to a stupid onlooker/newcomer so patiently :p

A little bit back on topic and yet another question; As of now the common word is; there are ten dimensions. The point however is... It's ten dimensions we can imagine to exist, who says there is no 11th, 12th... one? (Although I once heard of somebody claiming something about a 11th dimension but I can't recall it)

14. Apr 4, 2013

### phinds

No, there are not. There is a THEORY, called "string theory" that requires multiple dimensions but as of now there is exactly ZERO evidence that string theory has any meaning in the real world.

There is great hope that it DOES have meaning, because it holds out the possiblity of explaining things in a more fundamental and elegant way than any existing theory, but as of now it is pure speculation.

15. Apr 4, 2013

### Staff: Mentor

Perhaps, but even if it collapsed, would it really make a big difference in our everyday lives? No, not at all. We would still go on using the same math and models until something better or easier is developed.

No, that is not the common word. There are 4 known and accepted dimensions. String theory is not an accepted, mainstream theory. This is because it has not been verified yet in any way. It is purely in its theoretical phase still and could be trumped by something else. Anyone telling you there are more than 4 dimensions is pushing forth unverified physics.

16. Apr 4, 2013

### Gacha

I was aware that it's all speculation, sorry if I made it sound a bit too 'given'. The whole thing seems very well thought and would indeed explain a lot. The actual meaning for the real world is to be waited out, but as Crazymechanic said before it won't make our burgers taste any different. We also have to consider it's still a very new theory and nowhere near complete in any direction. If the basis we now have is going to be proven, extensions might be added that would explain more/give us more insight on other things.

The prior question was plainly about the most common way of thinking as of now, which appears to be the magical number 10 in string theory. The tenth dimension is supposed to contain all possibilities for all possible timelines for all possible universes so ultimately there should be a cap as there is no more space in our imagination for another two points to create the next dimension.

17. Apr 4, 2013

### Gacha

Looks like I answered it myself. In maths we could create up to 26 (some cases and instances even 28) valid dimensions on paper, but the common sub-theory is just the 10D one with D-branes

speaking of maths, I'm having quite a hard time understanding some notations and operators/symbols I have never seen before, is there any advanced reference that goes beyond the usual shinaningans that is reliable to use?
(a more specific example: in this Invariant for the heterotic superstring model - what does this vertically mirrored 'L' between L and $\mu$ mean/stand for?)

18. Apr 4, 2013

### Vorde

Sounds dubious at the very least to me, where did you hear this?

The reason people throw around 10 dimension (or 10+1 dimension theories where the +1 is a time dimension) theories is, as I read from a book (albeit a popular science one), because the current research is that M-Theory might be 'workable' in 10+1 dimensions.

But there are lots and lots of theories that say otherwise. Many stick with our familiar (thanks to Einstein et al) 3+1 dimensions, some have 10 dimensions, some 11 and some 28 and still others with many more. There is as of yet no evidence to suggest that the universe has any more than 3 dimensions of space and 1 dimension of time.

19. Apr 4, 2013

### Vorde

Why only 26?

Generally it means Christoffel symbols: http://en.wikipedia.org/wiki/Christoffel_symbols

20. Apr 4, 2013

### Gacha

I just haven't heard of many other things yet so it might just be that I take things I recently caught up on for too granted. I should get rid of that gullibility as soon as possible.

Just as above, the equation I saw was only valid for this many dimensions the way I understood it. Thus I have just taken it that way since I didn't know any better, so never mind :)

Thanks a lot for the hint, really helpful!

Last edited: Apr 4, 2013
21. Apr 4, 2013

### Omega0

Okay, I did not read every posting here but there should be something clarified: There is a pretty big difference between the four dimensions of SRT (and GRT): You can call the four x_i, x_j, x_k and x_m, but I am not sure why in this thread it is not told that - let us say x_m is the time - the light sphere is (x_i)^2+(x_j)^2+(x_k)^2=(x_m)^2? You can reorder and call it whatever you want - but the "time dimension" is not the same a space dimension?! You should clearly point that out.

22. Apr 5, 2013

### Turion

Where did you hear this? This isn't even string theory. This is pseudoscience.

Whoever told you this nonsense is most likely not a physicist, is not educated, is making things up and is lying to you. It doesn't make sense for a dimension to contain anything. A dimension is a degree of freedom. Unlearn what this person had taught you.

You need to be more careful when learning physics. Don't just trust any information anyone gives you. Do your research to see if they actually are a physicist.

Last edited: Apr 5, 2013
23. Apr 5, 2013

### Crazymechanic

It actually doesn't matter who tells you what all it matters is are you being told the truth or lies easy as that.
ofcourse it is easier to learn in sites like this one where there are people who sort out fake things but it's not like everyone needs a Phd to understand or be qualified to open his mouth.
As long as the person is right it's ok.But just as every teacher also every student or self taught especially has the responsibility not only to demand and seek information but to also check the validity of it.
Even professors can get things wrong or messed up we all are just humans you know.
But believe me and I can assure you both Gacha and others the one who seeks always finds.It jst is like that.
Now in the end of the day most of the time when one gets something wrong it's not because he would have been deliberately tough wrong rather it was his or hers choice to follow up some explanations that are not right.

i know many crackpots who have actually some pretty good skills and thinking they just reject the reality because they like what they make up more than what someone else has validated and experimented.

The things that we like an accept are the ones that make us who we are.

24. Apr 5, 2013

### Staff: Mentor

OK, I think that this thread has outlived its usefulness. The idea of time as the fourth-dimension comes from special relativity. It is incredibly well-validated experimentally:
http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html

If you have follow-up questions about relativity, please post them to the relativity forum.

The idea of more than 3 spatial dimensions is associated with string theory and its spinoffs. If you have follow-up questions about that, please post them to the beyond the standard model forum. Be sure and read the sticky before posting there. That forum is not for personal theories.