# How Many Dimensions Are There? **URL:** \ **Category:** Factual Questions\ **Created:** [January 22, 2018, 4:00pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215 "2018-01-22T16:00:33Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [January 30, 2018, 6:46pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/81 "2018-01-30T18:46:45Z")
Can we talk about spin foams (as in quantum gravity) now? What kinds of spaces are needed to make them work physically? Is there still an actual manifold (or orbifold) in the picture, like in normal quantum field theory? ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [January 30, 2018, 6:52pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/82 "2018-01-30T18:52:31Z")
> [@Exapno\_Mapcase](#): > > Have the people arguing against the mathematicians and physicists ever been right in any thread? Rightness doesn’t matter. When one side repeats their claims essentially verbatim without offering any additional evidence the thread is over. The thread can be about physics or fast food. The side can be one person or many. The overall pattern is always the same. If you spot it, get out after round three. To be fair, describing these contexts in text really doesn’t work very well. Math is the language of physics, and analogies always break down, especially when communicating concepts that are well past our human ability to intuitively understand. Brian Greene is one of the most famous string theorist, and has several videos that may be more accessible. Here is a long one that will answer a lot of the questions in this thread without math. [![]( " - YouTube") ](https://www.youtube.com/watch?v=oVoBn-mqrDI) But I would note that while less rigorous discussions on the internet can seem to resort to tautology, if you just watch enough to notice how careful they are about absolutes and claims it is a fairly good filter method. When dealing with a communication barrier either due to the limitations of a platform like this board, or just our language it can reduce to tautology. For the benefit of those trying to follow a autodidact path to learning, and not assigning motivation or blame to any poster or individual, any discussion about physics that is making absolute claims should be viewed with suspicion or caution. Physics is descriptive not prescriptive, but human nature and other limitations can cloud that fact with no active intent on the part of any actor. As I reminder I hope string theory is true, even supersymmetry has eluded testing so far, it is a hypothesis right now. It is still the best bet we have at the moment but it is unable to make predictions at this point and is in nowhere close to being proven or even tested at this point. This may be frustrating if you want an answer but this is also the reason people are working on it. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [January 30, 2018, 6:57pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/83 "2018-01-30T18:57:21Z")
> [@rat\_avatar](#): > > Brian Greene is one of the most famous string theorist, and has several videos that may be more accessible. I’ve read three of his books and I’ve been known to cite them enthusiastically in appropriate threads. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 30, 2018, 6:57pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/84 "2018-01-30T18:57:29Z")
> [@](#): > > Quoth **rat avatar** : > > I looked through the thread for a cite on a “factual answer”, can you help me understand by pointing out one that demonstrates that a prediction can be made that requires more that 3 spacial and 1 temporal dimension? Sure. If I’m trying to predict whether you’ll like a particular brand of beer, just knowing where the beer is, and when it’s served, won’t help me much at all. But if I put both the beer and your preferences in a five-dimensional space according to hoppiness, paleness, and so on, then I’m likely to be able to make a very good prediction. ---
**Author:** ![Itself](https://avatars.discourse-cdn.com/v4/letter/i/d07c76/32.png) [@Itself](https://boards.straightdope.com/u/Itself)\ **Post date:** [January 30, 2018, 7:00pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/85 "2018-01-30T19:00:39Z")
> [@DPRK](#): > > Can we talk about spin foams (as in quantum gravity) now? What kinds of spaces are needed to make them work physically? Is there still an actual manifold (or orbifold) in the picture, like in normal quantum field theory? Absolutely. This really isn’t my field at all, but it looks like it takes place in ordinary spacetime. The spin foams themselves are just finite 2-complexes (or, equivalently in low dimensions, 2-manifolds, but the explicit 2-skeleton is used). The idea is that you can hook up spin network approaches to the the usual Feynmam path integral with the spin foam showing how the space spin networks fit together in time. But that handwaving approach is as far as I got skimming a few random papers. ---
**Author:** ![Scylla](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@Scylla](https://boards.straightdope.com/u/Scylla)\ **Post date:** [January 30, 2018, 7:05pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/86 "2018-01-30T19:05:19Z")
I’m not sure how many physicists or mathematicians there actually are here. I’m guessing not many, as those insisting that there are more than 3 dimensions as an established fact are making the mistake of taking proposed models and theories more literally than the ones who made them. Nobody asked me for a cite but there is a complaint that none have been provided. Ok. > **[How Many Dimensions Does the Universe Really Have?](https://www.pbs.org/wgbh/nova/article/how-many-dimensions-does-the-universe-really-have/)** > > Discover why physicists think our universe may have ten dimensions—or more. That one says there are 3 that we know about, maybe more in theory, some that we are actively searching for evidence of, but right now 3? > **[A Universe of 10 Dimensions](https://www.universetoday.com/48619/a-universe-of-10-dimensions/)** > > When someone mentions “different dimensions,” we tend to think of things like parallel universes – alternate realities that exist parallel to our own but where things work differently. However, the reality of dimensions and how they play a role in... This one says 3, and that scientists think time may be number 4, but they are not sure, and that superstring theory says that maybe there is more but they are not sure yet. > **[What is a dimension, and how many are there?](https://science.howstuffworks.com/science-vs-myth/everyday-myths/dimension.htm)** > > Forward and back, left and right, up and down -- most of us are familiar with these spatial dimensions. We might even pinpoint our location in time. Is that all there is to dimensions? No way, say the scientists who have a theory for everything. This one says 3, and maybe more depending on how we look a time and depending on whether or not string theory holds water there could be more. Those are the first 3 links from google when you ask it how many dimensions there are. It looks like a consensus too me. So, what I said first stands. There are 3. Any thing more than that is at this time a theory, a model, or a proposition or an analogy. So, the scientists and the mathematicians actually agree with me. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [January 30, 2018, 7:08pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/87 "2018-01-30T19:08:38Z")
> [@Chronos](#): > > Sure. If I’m trying to predict whether you’ll like a particular brand of beer, just knowing where the beer is, and when it’s served, won’t help me much at all. But if I put both the beer and your preferences in a five-dimensional space according to hoppiness, paleness, and so on, then I’m likely to be able to make a very good prediction. Those are parameter spaces or configuration spaces, and I have never argued those may not exist as a useful convention or mathematical construct. Movement in any other direction can be expressed in terms of just three spatial dimensions, and GR in 4 with the addition of a temporal dimension. The reason I have an issue with the parameter spaces or configuration spaces in relation to string theory is that the interactions cannot be reduced to 4 dimensions of spacetime and the math requires those additional dimensions to function. When a poster is asking if they should _believe_ that these dimensions are _real_ based on a hypothesis that has eluded any testing and has failed to make any predictions to this point it becomes a problem in a GQ context. But feel free to explain why I shouldn’t place it in the same category as Russell’s teapot? Also explain why prominent physicists as I have cited above make quite clear statements about claims of _belief_ at this stage and very careful qualify their statements. I cannot discount mathematical constructs or conventions, but to claim that the additional dimensions are purely parameter spaces in string theory seems to discount the very reason they exist in that framework. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [January 30, 2018, 7:12pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/88 "2018-01-30T19:12:20Z")
> [@Scylla](#): > > I’m not sure how many physicists or mathematicians there actually are here. I’m guessing not many, as those insisting that there are more than 3 dimensions as an established fact are making the mistake of taking proposed models and theories more literally than the ones who made them. > > Nobody asked me for a cite but there is a complaint that none have been provided. Ok. > > [How Many Dimensions Does the Universe Really Have? | NOVA | PBS](http://www.pbs.org/wgbh/nova/blogs/physics/2014/04/how-many-dimensions-does-the-universe-really-have/) > > That one says there are 3 that we know about, maybe more in theory, some that we are actively searching for evidence of, but right now 3? > > [A Universe of 10 Dimensions - Universe Today](https://www.universetoday.com/48619/a-universe-of-10-dimensions/) > > This one says 3, and that scientists think time may be number 4, but they are not sure, and that superstring theory says that maybe there is more but they are not sure yet. > [What is a dimension, and how many are there? | HowStuffWorks](https://science.howstuffworks.com/science-vs-myth/everyday-myths/dimension.htm) > > This one says 3, and maybe more depending on how we look a time and depending on whether or not string theory holds water there could be more. > > Those are the first 3 links from google when you ask it how many dimensions there are. It looks like a consensus too me. > So, what I said first stands. There are 3. Any thing more than that is at this time a theory, a model, or a proposition or an analogy. > > So, the scientists and the mathematicians actually agree with me. My understanding (unless I missed some discoveries) of the currently tested theories is that the minimum number of dimensions needed to describe a position are three spacial and one temporal (time). There are some theories in the quantum world that add dimensions to reduce the math complexity, and then there are others that add them as required features for the theory to work. If String theory ends up being validated, it will require additional dimensions that will be just as _real_ as those above dimensions. meaning that you cannot reduce the number of dimensions and still describe the system. But we are not there yet. But yes your questions seem to be describing the minimum number needed dimensions to describe a system, when other posters are explaining ones that may be potentially required in the future if current guesses happen to be true or other sets that make various operations more convenient. Or to be more exact I think this is where the parties are talking past each other. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 30, 2018, 7:15pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/89 "2018-01-30T19:15:16Z")
Oh, if you mean additional dimensions _of spacetime_, then yeah, that’s all just hypothetical, and even if they’re real, it’ll probably be a very long time before they’re proven. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 30, 2018, 7:16pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/90 "2018-01-30T19:16:07Z")
Oh, if you mean additional dimensions _of spacetime_, then yeah, that’s all just hypothetical, and even if they’re real, it’ll probably be a very long time before they’re proven. EDIT: So, yes, if you prefer to work under the assumption that they don’t exist, that assumption won’t hurt or hinder you at all. ---
**Author:** ![Itself](https://avatars.discourse-cdn.com/v4/letter/i/d07c76/32.png) [@Itself](https://boards.straightdope.com/u/Itself)\ **Post date:** [January 30, 2018, 7:19pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/91 "2018-01-30T19:19:53Z")
> [@Chronos](#): > > Oh, if you mean additional dimensions _of spacetime_, then yeah, that’s all just hypothetical, and even if they’re real, it’ll probably be a very long time before they’re proven. > > EDIT: So, yes, if you prefer to work under the assumption that they don’t exist, that assumption won’t hurt or hinder you at all. …which is exactly what you and I and others have been saying throughout this entire thread. Cool. Hey, Chronos, what do you know about spin foam? That’s a much more interesting subject. ---
**Author:** ![Scylla](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@Scylla](https://boards.straightdope.com/u/Scylla)\ **Post date:** [January 30, 2018, 7:27pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/92 "2018-01-30T19:27:57Z")
Another thought on this. String theory says you need to have 10 or is it 11 dimensions, but so far there is no evidence that they actually exist. It is just a construct, a model that is being used to explain things, and may be useful for its ability to do so. It may be right, it may be wrong, it will likely tcontinue to be modified as we throw more things at it that we want explained. Similarly we have this stuff called “dark matter.” Dark matter was invented to explain the fact that the universe behaves very differently from the way it should compared to all the other hard won knowledge that we are pretty sure of. Nobody has seen it, touched it or found any evidence for it whatsoever. The only form of evidence for it is that we need it to exist in order for our understanding of the behavior of the universe to make sense. Just because you need something doesnkt make it there. There are at least three other viable options. 1. It’s something else entirely that will seem obvious in retrospect and future scientists will laugh at our silly scientists who believed in dark matter the way we laugh at the scientists of the past who thought that rotting corpses spontaneously generated maggots. 2. Our head is so completely up our ass in terms of even our most basic understanding of the cosmos that our standard model bears about as much resemblance to reality as the four bodily humurs model bore to pathology, and we will be hopelessly lost until we abandon it and start again. 3. Our biology and perception traps us into seeing things and thinking about them in a certain way, and the way things are cosmoligically speaking is incompatible with the way we are capable of perceiving and thinking and we have reached the limits of knowledge in these particular areas. In other words the laws of the universe are on a cd rom, and all we have is a record player. “Dammit why won’t it play!” ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [January 30, 2018, 7:32pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/93 "2018-01-30T19:32:00Z")
> [@Itself](#): > > …which is exactly what you and I and others have been saying throughout this entire thread. Cool. Hey, Chronos, what do you know about spin foam? That’s a much more interesting subject. Yet you discounted my response to post #57, where this EXACT question was asked. This is why I asked you to re-read that post. > [@](#): > > One group is using the informal definition as the minimum number of coordinates needed to specify any point within it, and others are talking more about parameter spaces or configuration spaces etc… > > This is what Itself is talking about here. \ > [@](#): > > But for the three spatial dimensions and three angles of rotation can be reduced to three spatial dimensions, where the 10/11/XX dimensions in string theory are not exactly like that. I continued to respond due to dismissals and asked for cites and clarification, which were dismissed. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [January 30, 2018, 7:34pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/94 "2018-01-30T19:34:11Z")
> [@Scylla](#): > > Another thought on this. String theory says you need to have 10 or is it 11 dimensions, but so far there is no evidence that they actually exist. It is just a construct, a model that is being used to explain things, and may be useful for its ability to do so. It may be right, it may be wrong, it will likely tcontinue to be modified as we throw more things at it that we want explained. > > Similarly we have this stuff called “dark matter.” Dark matter was invented to explain the fact that the universe behaves very differently from the way it should compared to all the other hard won knowledge that we are pretty sure of. > > Nobody has seen it, touched it or found any evidence for it whatsoever. The only form of evidence for it is that we need it to exist in order for our understanding of the behavior of the universe to make sense. Just because you need something doesnkt make it there. There are at least three other viable options. > > 1. It’s something else entirely that will seem obvious in retrospect and future scientists will laugh at our silly scientists who believed in dark matter the way we laugh at the scientists of the past who thought that rotting corpses spontaneously generated maggots. > > 2. Our head is so completely up our ass in terms of even our most basic understanding of the cosmos that our standard model bears about as much resemblance to reality as the four bodily humurs model bore to pathology, and we will be hopelessly lost until we abandon it and start again. > > 3. Our biology and perception traps us into seeing things and thinking about them in a certain way, and the way things are cosmoligically speaking is incompatible with the way we are capable of perceiving and thinking and we have reached the limits of knowledge in these particular areas. In other words the laws of the universe are on a cd rom, and all we have is a record player. “Dammit why won’t it play!” The difference between dark matter and energy is that they help explain observations today and there have been tests that infer their existence and predictions that have been matched with observations. String theory has difficult challenges in reaching that state, but hopefully they can find ways to work around those limitations in the future. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [January 30, 2018, 7:58pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/95 "2018-01-30T19:58:54Z")
> [@](#): > > 1. It’s something else entirely that will seem obvious in retrospect and future scientists will laugh at our silly scientists who believed in dark matter the way we laugh at the scientists of the past who thought that rotting corpses spontaneously generated maggots. I should also point out that superseded or obsolete theories can be found to be inadequate or incomplete description of reality, or simply false. In some cases like Newtonian physics the theory is incomplete, but not falsified and still useful in a large number of cases. Some theories like phlogiston were fully falsified and are no longer used. We know that both GR and the Standard models are incomplete but that does not mean that they are fully falsified and discarded. It just means that we have more to learn. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 30, 2018, 8:08pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/96 "2018-01-30T20:08:10Z")
There is no evidence for the String Model. There is abundant evidence, of many different independent forms, for dark matter and for dark energy. We know very little about dark matter, and almost nothing about dark energy, but one thing that we do know is that they exist. ---
**Author:** ![Pasta](https://avatars.discourse-cdn.com/v4/letter/p/ecccb3/32.png) [@Pasta](https://boards.straightdope.com/u/Pasta)\ **Post date:** [January 30, 2018, 8:54pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/97 "2018-01-30T20:54:08Z")
I’m just reading this thread. I’m not entirely sure how it went off the rails so badly, but the reason it stayed there was that even after it was clear that there is a semantics issue, the discussion (largely) ignored that point. _How many [known | hypothesized with good reason | hypothesized with flimsy reason] [spatial | spacetime | generic but physical | completely generic] [dimensions in the technical sense | dimensions in the lay sense] are there?_ Pretty much all of those 24 possible questions – and their answers – have representation in the thread somewhere. Pick a question, and the answer can be given. But it isn’t fighting ignorance to argue over which question is the right question. They’re all fine questions. For what it’s worth, I take the OP to be mostly interested in the question “_How many [known] [spacetime] [dimensions in the lay sense] are there?_” but with a side interest in any discussions about “_How many [hypothesized for good reason | hypothesized for flimsy reason] [spacetime] [dimensions in the lay sense] are there?_” These have all been answered factually above. > [@Scylla](#): > > Similarly we have this stuff called “dark matter.” Dark matter was invented to explain the fact that the universe behaves very differently from the way it should compared to all the other hard won knowledge that we are pretty sure of. > > Nobody has seen it, touched it or found any evidence for it whatsoever. This is incorrect. Dark matter is very well established as a Real Thing, much more so than many other things that you likely consider Real Things. (Dark energy is a different beast and much more… parametrized. Dark _matter_ is definitely actual stuff in actual space with a relatively narrow range of known properties.) ---
**Author:** ![Scylla](https://avatars.discourse-cdn.com/v4/letter/s/a5b964/32.png) [@Scylla](https://boards.straightdope.com/u/Scylla)\ **Post date:** [January 30, 2018, 9:03pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/98 "2018-01-30T21:03:14Z")
Pasta: Other than “we know it has to be their for our model of gravitation to work, and we are really sure about our model.” How do we know dark matter is definitely real? ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [January 30, 2018, 9:19pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/99 "2018-01-30T21:19:24Z")
> [@Scylla](#): > > Pasta: > > Other than “we know it has to be their for our model of gravitation to work, and we are really sure about our model.” How do we know dark matter is definitely real? One of the most accessible examples is gravitational lensing as a result Dark Matter that matches Einstein’s predictions. > **[The Nature of Dark Matter](https://www.lsst.org/science/dark-matter)** > > Dark matter, which makes up about 85% of the mass in the Universe, is more than simply dark. True, it can't shine by its own light, like hot coals, or even reflect light, like clouds or water. Neither electricity nor magnetism affect it. ---
**Author:** ![cmyk](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmyk/32/3353_2.png) [@cmyk](https://boards.straightdope.com/u/cmyk)\ **Post date:** [January 30, 2018, 9:30pm UTC](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215/100 "2018-01-30T21:30:44Z")
> [@rat\_avatar](#): > > One of the most accessible examples is gravitational lensing as a result Dark Matter that matches Einstein’s predictions. > > [The Nature of Dark Matter | Rubin Observatory](https://www.lsst.org/science/dark-matter) And [here’s a really good article](https://medium.com/starts-with-a-bang/five-reasons-we-think-dark-matter-exists-a122bd606ba8) from Starts With a Bang. [Previous page](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215.md?page=4) [Next page](https://boards.straightdope.com/t/how-many-dimensions-are-there/807215.md?page=6)