# Dimensions and time

1. Jun 22, 2013

### michojek

So I watching this video on dimensions..
and I have a few questions:
1. How many dimensions are there? (that are proven with hard evidence)
2. The video was talking about 4-Dimensions - is it pretty much the same thing as 3-Dimension + time?

2. Jun 22, 2013

### bapowell

Yes, that's right. Spacetime is 4-dimensional: 3 dimensions of space and 1 of time. This conception of a 4-dimensional universe is based on Einstein's theory of relativity, which reveals that space and time are not distinct, independent entities.

3. Jun 22, 2013

### Jheavner724

I will as a String Theory perspective to this. Although String Theory has not get been tested through experimentation, it has beautiful thought and mathematics behind it, so it should be considered a viable possibility for the mechanics of the universe. In String theory there are typically either 7, 10 or 11 dimensions, depending on the particular sub-topic or the opinions of the physicist (although 26 and even infinite dimensions have been theorized, but with less prolific mathematics and thought). If you're wondering about these dimensions you can surely google it and find tons of information. There is a lot that goes with it and it's all still theoretical, but it includes concepts like super-symmetry and membranes.
As for the proven dimensions, there are 4, as the other answer said. But, these are still technically theoretical too, just because this stuff is hard to "prove". Hence, being the "theory" of relativity.

4. Jun 22, 2013

### Jheavner724

Correction to my first post, "as" should be "add".

5. Jun 22, 2013

### micromass

What do you understand under "proof" and "hard evidence". In a sense, the only thing that you can prove is that there are minimum 3 dimensions.
Do you consider relativity theory to be proven with hard evidence? And if you do, does that necessarily imply that the mathematical constructs of spacetime are actually real?

6. Jun 22, 2013

### Jheavner724

I consider Relativity to have some evidence, actual tangible evidence, because there have been some experiments. But, the ideals of relativity have shown time and time again to be true, so it is generally considered to be quite factual, although likely incomplete. String theory is not nearly as close to being proven, but it has good concepts, ones that are plausible (although intuition may tell you they seem odd, much like relativity). Also, mathematical evidence IS evidence for the possible existence of something, and can sometimes even be good enough to be called proof. String theory is in no way proven, but it pertains to this question and has a fair likelihood of being found to be true. Relativity, on the other hand, is used all the time in science, because it is almost definitely true, however it is not definitely proven through experimentation and tangible evidence. But, it is also near impossible to test some of these concepts in a lab, like ones in string theory or relativity, but string theory is very new and still has many things to be worked out, I realize that. Both theories are incomplete, as is quantum theory, and they are not proven, hence them being called theories, but they are useful and almost surely have some truth. For example, Muon's (a type of particle) should never be found here on Earth according to proven scientific ideas. However, they are found quite often on Earth and when relativity is applied, it shows why and how. Similar implicit evidence, along with mathematics, are why many people consider string theory to be so viable.

7. Jun 22, 2013

### Jheavner724

Oh, I forgot to say that, for relativity, there is actual "hard evidence" now, along with many "implicit" proofs, however, string theory has no such "hard evidence". Also, the mathematical constructions of relativity have proven to be true over and over, like the muon example, so, yes, I do consider them to be quite accurate (however not entirely proven and maybe not complete). Similarly with string theory, the mathematics is valid, also the aforementioned "implicit proofs" seem to make the validity of string theory even more plausible. The facts are, that all of these theories that are studied are only studied because they are probably true, we just need to prove it. Although, I admit that string theory (in some aspects) may be pushing it a bit, or just be a little off, but the theory is valuable nevertheless.

8. Jun 22, 2013

### Jheavner724

There is no "hard evidence" for string theory, but a lot of implicit evidence. With these new ideas that are some complex and intangible, it is difficult to get "hard evidence". We have never observed something moving at the speed of light other than light itself, also we cannot test things like the Twin Paradox solution. Relativity, like string theory, are practically untestable in the traditional sense of the word. However, if you make a theory, and then there's a bunch of things people cannot answer about the universe, but it does, then isn't it worth something? Also, relatively predicted things like black holes and more, is that not something? I know, there is no "hard evidence", there probably won't be for another hundred or more years, but imagine if we never used relativity. Relativity has proven so useful and effective that it is almost impossible to say the whole thing is wrong, it is probably just somewhat incomplete (hence it not being the ToE).

9. Jun 22, 2013

### Jheavner724

Alright, I don't want to argue with any one, but I feel like that's how this is going to turn out. Relativity is probably right, it's done so much for science it isn't even funny. String theory may very well also be correct. However, neither have hard evidence or are proven, but rely on mathematics and implicit proofs to validate their claims. I said in my original post that string theory was not experimented (thus not proven), but I also think it is helpful to still provide the information, because one day relativity and string theory may be proven. Nevertheless, relativity has been one of the greatest accomplishments in physics, and string theory may be the beginning of the same sort of revolution (although it surely cannot be said for sure yet). Furthermore, it is almost impossible to test either theory or ones like them. But, many years ago, there probably wasn't even a proof for one dimension existing, let alone three or more. As of now, in the strictest sense of the statement, based on hard evidence there are only three proven dimensions to exist. However, it is almost positive that time is the fourth, and likely that there are many others. This is both my revised answer, my explanation and my apology for not entirely following the constraints of the question, I am really sorry if my answer was a wasted one. However, I did not think such strict constraints were intended, because then I thought the answer to be very counterproductive and maybe even a bit obvious, nevertheless I hope this is interesting or helpful to someone.

10. Jun 22, 2013

### michojek

thanks guys for the replies!
seems like relativity is an pretty solid evidence for 4-D
I also looked up string theory and its dimensions.. It said there are maximum of 10 dimensions.
However I thought about it and came to this conclusion,
0-D = dot
1-D = line
2-D = plane
3-D = 3-D plane
4-D = 3-D plane + time
5-D = 3-D plane + time + all possibilitie
6-D = 3-D plane + time + all possibilities + different universes (different laws of physics)
so 6-D contains everything..so, I'm a little confused how can there be 10?

11. Jun 23, 2013

### Jheavner724

P.S. Check out quantum mechanics and quantum theory, it is one of the most important physics ideas ever, being established near the time of Relativity.

12. Jun 23, 2013

### julian

Einstein didn't like the idea that extra dimensions weren't subject to the same dynamical laws of GR. But if you do subject them to GR doesn't Penrose complain that there will be instabilities - either the propositions of the singularity theorems apply or the extra dimensions grow so large as to be observable?

13. Jun 23, 2013

### Jheavner724

There are many problems in String Theory, and that is one of the current ones. There are tons of contradictions, even Relativity and Quantum Mechanics contradict String Theory. Now you probably think it is all nonsense, but I assure you it is't. String Theory may not be completely right, but it is surely onto something (much like the Theory of Everything [ToE]). The same thing actually applies to Relativity and Quantum Theory, they have problems too, although often it is simply a matter of being incomplete, which is part of the motivation for the ToE (well, more like it gave physicists an excuse to ponder such an astounding theory). Another big problem, in every physics theory, is gravity and why it is so weak, but String Theory addresses this problem with Super-Gravity and other things. The truth is that I would need to go into profound detail that, unless you have studied physics and mathematics extensively, you would probably not understand. However, it can be said, that String Theory is truly beautiful and should be taken seriously. Hopefully, one day, a Theory of Everything will be made, unifying and perfecting all of the theories that we are discussing.

14. Jun 23, 2013

### Jheavner724

Also, regarding the Penrose-Hawking Singularity Theorems, I will just remind you that Hawking is one of the people whom are working on the Theory of Everything, and the ToE involves tons of String Theory. So, considering the co-creator of the theorems is such an enthusiast of String Theory, I think you can see that it doesn't necessarily inherently contradict the theorems in a way that should prompt you to doubt the theory.

15. Jun 23, 2013

### julian

I think there are problems with string theory...with my admittedly extremely limited knowledge...but I still think it could be right...I'm of the opinion, same as Smolin and Mr Brian Greene, that background independence could be the answer to many of the "problems" string theory faces and as Greene thinks (Fabric of the universe I think) could bring about a 3rd revolution in string theory.

16. Jun 23, 2013

### Jheavner724

Unlike most people that talk about these things, I actually do have enough knowledge to talk about this (I have taken 3 different String Theory related OCW courses, also I have read books, done internet research and read many papers on the topic, now I am actually working on my own theories/research). With that being said, you are largely correct in my opinion. There are many problems with String Theory, but even in well-established and accepted theories like Relativity there are problems. Also, String Theory is still so young that flaws are expected, so, in general, know that this theory could be entirely right, but is almost definitely "onto something". As far as "background independence" goes, I agree and disagree. The fact is that it is near impossible to be entirely background independent, however I believe that more researchers should include practicing some amount of background independence in their work. I would also say that the "third revolution" in String Theory is possible and likely coming soon, maybe even thanks to background independent thinking and ideas. Also, I would like to point of that String Theory is sometimes thought to be, by many people, an extension of Quantum Theory and Quantum Mechanics, and that is somewhat true. My point with that is that maybe String Theory should be, at least with regards to our thinking, grouped together with Quantum Theory.

17. Jun 23, 2013

### julian

I'm more in the LQG camp because they have made such strides towards understanding background-independent quantum field theories - not perfect, not complete but they have learned a lot. And I think there should be more sharing with string theorists.

18. Jun 23, 2013

### Jheavner724

They have made huge strides, you're entirely correct. In my opinion, pretty much the only way a "Theory of Everything" or a similar theory will happen is by thinking primarily background-independently and then, at least in some way, combining many theories (e.g. combining Relativity with Quantum Theory and String Theory).

19. Jun 23, 2013

### julian

With regards to extensions to quantum mechanics...background-independence implies the idea that there is no absolute time and in fact time must be thought of as represented by some physical variable that must be part of the physical system under study...this has lead to interesting new interpretations that are of worth mentioning - for example the Montivideo interpretation of quantum mechanics: the fact that real clocks are quantum mechanical introduces a new fundamental decoherenece that circumvents the problems of traditional decoherenece `expalanation' and claims to resolve the measurenment problem and also the problem of outcomes...so much to learn off each other...and possible overlaps

Last edited: Jun 23, 2013
20. Jun 23, 2013

### julian

It's great we are getting people working on their own research contributing here!!!

21. Jun 23, 2013

### Jheavner724

Absolutely, it is great to encourage the search for knowledge. As far as your older post, you have some great points there. One of the great things about physics is that you can theorize almost anything and interpret a topic in almost any way (assuming that these are factually-based), it is until the theories are proven or confirmed that more restrictions on thought exist. However, that is also a great thing about physics, discovering new truths about the universe is exciting.

22. Jul 19, 2013

Richard Feynman said nobody understands Quantum Theory. The Universe is Quantum, understand what it is telling you and you will have your Theory of Everything. All you need to know is all ready available and has been since Feynmans time.

23. Jul 19, 2013

### Jheavner724

Much easier said than done. Also, the Theory of Everything may include information that in not yet readily available. Also, Feynman was correct in a sense, but if you take his statement as being broad and entirely literal then it becomes misleading. Physicists understand quantum theory to an extent, but struggle with specifics, exceptions, problems and interpretations, also quantum theory is a bit unintuitive for almost everyone.

24. Jul 22, 2013

Do not worry about Theories of Everything I can assure you it is not what you or anyone else thinks it is, I could quote the bible but it is frowned upon in this forum.
I have been thinking, you are a string theorist and it sounds well qualified, the thing I have against string theory is the extra dimensions needed.
You are doing research and I offer an alternative to the extra dimensions.
Instead of having tiny curled up dimensions make them the same size as our universe but slightly out of phase in time yet existing in the same space, the time differential should automatically set up forces between the different universes, some or all may push, some or all may pull depending on how things are set up.
This turns string theory, brane theory and associated theories into a branch of multiverse theory which is more plausible and I believe more accurate, in other words stop trying to hide dimensions in space when you can hide whole universes in time, make life easier for yourself.

25. Jul 22, 2013

### bapowell

And this is somehow less objectionable than compactified extra dimensions? Why?