# Can we actually prove with 100% certainty that there are more than 3 dimensions plus time $(t,x,y,z)$? [duplicate]

Can we actually prove with 100% accuracy that there are more than 3 dimensions plus time?

In the news there are always articles like "there are probably 7, 11 or more dimensions", "time is actually not a 4th dimension" etc.

My question is:

Could we be 100% sure that there are more than 3 dimensions and what field of physics except some theoretical or hypothetical branches of physics and mathematics take that in count that there are more than 3 dimensions plus time?

I know the example of a 2D "creature" being unable to see 3D creature (maybe only the interference when the 3d object collide with the 2d world. But I can argue that there are no 2d or 1d beings like in that episode of Star Trek. So, this proof is only an illusion and all we see is 3d and not 1d or 2d. the light itself is bending in space-time depending how the object looks.

I think that 1d or 2d objects can not exist in 3d world at all and it's just an illusion we created, the same way as we speak about 4th,7th etc. dimensions and probably it's all 3d (or chose the name as you wish).

Is this guy correct that 3 dimensions and time is all we need?http://mathematicalmulticore.wordpress.com/2010/04/23/four-dimensions-a-simple-proof/

Could it be that we are creating other dimensions only because we don't understand our Universe good enough?

I mean, don't get me wrong, but the whole 7,11,21,1000-dimensions seems to me like a marketing, something too provincial (as Feynman would say), something like... religion ;D.

• Possible duplicates: physics.stackexchange.com/q/10527 and physics.stackexchange.com/q/4079 – jinawee Dec 12 '13 at 7:31
• Science isn't about 100% proof: that's maths, not physics. – 410 gone Dec 12 '13 at 7:33
• This is not a duplicate. There's a difference between a fourth spatial dimension and a temporal one. However, this is primarily opinion-based. – Abhimanyu Pallavi Sudhir Dec 12 '13 at 8:39
• The system is again putting VTC reasons in my mouth, I VTCed as primarily opinion-based.. – Abhimanyu Pallavi Sudhir Dec 12 '13 at 15:20

## 2 Answers

We could easily prove that more than four dimensions exist simply by observing a fifth dimension, but proving that only four dimensions exist is much harder and probably impossible. This is an example of the general case that proving something doesn't exist is usually impossible outside the halls of Mathematics.

I wouldn't stake my life on no proof being possible. It's conceivable that someone might come up with a potentially observable feature of the universe that couldn't exist if there were more than four dimensions. However any such argument would almost certainly require assumptions that could be challenged by the multidimensionalists.

The blog post you link doesn't prove anything. It argues that the observable universe is compatible with there being four dimensions, so extra dimensions aren't necessary, but it gives no proof that extra dimensions can't exist.

Some footnotes:

As far as I know there are no real (as opposed to mathematical) objects with 1 or 2 spatial dimensions. Everything has three spatial dimensions.

Time isn't the fourth dimension, or at least not for us physicists because we usually make time the first dimension i.e. we write spacetime coordinates as $(t, x, y, z, ... )$.

• Thanks, so you are saying that it's not 100% sure that there are more than 3 dimensions plus time? – Derfder Dec 12 '13 at 7:35
• @Derfder: right now there is no proof that more than four dimensions exist. – John Rennie Dec 12 '13 at 7:36
• Thanks, that's all I wanted to be sure of. That all these things speaking about more than time plus x,y,x are only hypotheses. Thanks. – Derfder Dec 12 '13 at 7:37
• @JohnRennie: I downvoted because a) it's an answer to an ill-posed question (one can hardly parse the bold sentence), which will hence only confuse b) The first statement is vacous and then you answer a negated variant of the question, which isn't asked for c) "As far as I know there are no real (as opposed to mathematical) objects with 1 or 2 spatial dimensions. Everything has three spatial dimensions." isn't consistent. d) And to say "Time isn't the 4th dimension" because some other isomorphic ording is convention doesn't answer anything. - A working notion of "proof" is also missing. – Nikolaj-K Dec 12 '13 at 13:12
• @Derfder actually it is even stronger, you got it backward. The current status is: there is not a single shred of evidence that there are more than 3 dimensions. So it is likely 99% sure that there are not more than 3 dimension plus time. – lalala Sep 24 '17 at 14:29

I'd like to point out that there is a big difference between the physical reality and the mathematical model describing it. Science has developed various mathematical models to describe the physical reality: the universe of Newton is $T\times E_3$ where $T$ is the time-axis (geometrically speaking, a copy of the real line) and $E_3$ is the euclidean $3$-dimensional space. Einstein's universe is a 4-dimensional Riemannian manifold whose global structure is way more intricated than Newton's. More recent models arising from the development of string theory and others have a bigger number of dimensions, for reasons that are too complicated to state here.

All these models can be used to predict some events within a certain degree of accuracy, but become unsatisfactory to give a full explanations of others.

Given this, what real sense does it make to say that physical reality has a given number of dimensions?

• We have trouble to see small articles. In fact we just "calculate" their presence, because of how other articles interacted etc. Therefore speaking about 11 dimensions is in my opinion just a speculation and theory and I get mad when some scientists want to kill you because they think that these mathematical "ideas" that works on their paper is how it really is. Look, if something is based on some kind of evidence, like the infrared or other light from the star and you measure it or some other thing that can be observed or measured, than OK. But when somebodys speaking about 11 dimensions?WTF? – Derfder Dec 12 '13 at 13:37