# Talk:Introduction to M-theory

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## Falsehood in text

[String theory] "... showed how ... all of the forms of energy in the universe could be constructed by hypothetical one-dimensional "strings", infinitesimal building-blocks that have only the dimension of length, but not height or width." This statement is false. As it stands, the statement describes a period of time during which most physicists wrongly believed that the cosmological constant was negative or zero. Since the late 1990s, we've had evidence that the value is positive. String theory does not explain this; in fact, it has not been demonstrated that string theory is even basically compatible with a universe having a positive cosmological constant (theorists call this "the search for de Sitter vacua"). — Preceding unsigned comment added by 50.43.34.193 (talk) 00:42, 6 July 2018 (UTC)

I'll take a stab at fixing that. Rolf H Nelson (talk) 17:21, 29 July 2018 (UTC)

Please, at the very least, remove the "all forms of energy" sentence. At best, I ask that we change the second sentence from "So far no experimental evidence exists showing that M-theory is a description of the real world" to something more in line with the truth, which is that string theorists have not been able to reduce M-theory to a set of predictive equations that even vaguely matches the real world despite decades of intense effort. — Preceding unsigned comment added by 50.43.34.193 (talk) 00:42, 6 July 2018 (UTC)

That sounds like editorializing; if there's a specific strong source we can consider including it as an opinion. Rolf H Nelson (talk) 17:21, 29 July 2018 (UTC)

## What does M mean

I think saying M stands for Membrane is most suitable, as It is obvious to understand that strings are one dmentional and strings may be considered as slices of a 2-dimensional membrane vibrating in 11-dimensional (or any other ) space.

• These terms may be considered correct as there is no any confident explanation what 'M' stand for.
"matrix", "mother" and "monster" are other names
some have even claimed "mystery" and "magic"
--User:P.nishantpathak (talk)29 december 2012
According to Sheldon Glashow, it's an upside down W for Witten KagakuKyouju (talk) 04:53, 27 January 2013 (UTC)
It's part of the charm of that name that nobody knows what the M stands for. — HHHIPPO 10:31, 27 January 2013 (UTC)

## Replace flawed article

I kind of like the idea of having an introductory level entry on m-theory, but I agree that the article was fundamentally flawed in many ways, so I decided to write my own. I would appreciate hearing your thoughts on it and whether or not you think it is still best to combine it with the regular M-theory page. Thanks. Jcobb 10:03, Feb 21, 2004 (UTC)

The use of words, as opposed to mathematical notation, is the right approach for the simplified article, which I propose to submit to Featured articles, if it is all right with you all. Ancheta Wis 18:46, 28 Feb 2004 (UTC)

Should this not be organised such that article is at "M-theory" and we give each section sub-articles where the more in-depth stuff goes? Joe D (t) 12:44, 17 May 2005 (UTC)

IMHO, it makes more sense to have the simplified article at M-Theory, and further information in (technical). The whole encyclopaedia is meant to be accessible to non experts, so a "technical" article is a departure from that. FWIW. 217.128.193.40 16:39, 6 January 2006 (UTC)
This article should eventually be merged into M-theory. We can't have different articles on the same subject. I do not agree, however, that all of wikipedia has to be accessible to a general audience. The technical stuff, should be farmed out into subarticles of M-theory.--345Kai 21:45, 11 October 2007 (UTC)

I think the present article is simple enough, however I may want to revert the replaced article M-theory simplified as a subpage within this article or else remove the redirect here. As time ceases to exist new information is available. BF (talk) 16:31, 23 August 2011 (UTC) I think original article (M-theory) is simpe enough. English is not my native language and am designer by education but I still understood that article, except for math. For what reason is to create another one for some hypothetical people who don't understood "difficult" articlr? I think we need at least merge them178.122.116.11 (talk) 16:35, 5 February 2013 (UTC)

## Greene or Green?

Is Greene spelled Green? I have it on the authority of Dr. Scott Wolpert, head of the math department at the University of Maryland, that it "probably has no e on the end" Sabrebattletank

Brian Greene is a known author. Nice appeal to authority, though. Have you seen his books in the stores?
Yup. Just checked out The Elegant Universe and the Fabric of the Cosmos. Thanks. Now, thanks to Greene, I am more versed in String Theory.Sabrebattletank 22:41, Apr 14, 2005 (UTC)

But there is also the Green of Green, Schwarz(sp) and Witten. --MarSch 15:38, 2 Jun 2005 (UTC)

## Approximation statement

If you are changing the radius from R to 1/R to change from theory to theory, I would appreciate some explanation of whereabouts '1' is - obviously not metres, or 1/R would be larger than a planet. How long is the unit in this case?

Probably the units are natural units, subject to transformation of variables. At this level, the names of the units are immaterial, as most of the 10, 11, 16, 26 dimensions don't even have names. So it's all abstract right now. --Ancheta Wis 01:42, 13 February 2006 (UTC)
1/R is also a general way to denote the multiplicative inverse of a number. Thus 1/R would have the same units as R (presumably meters). Since the extra dimensions are all spatial dimensions, they would be measured with meters (or units of length/distance of any type, natural units included). Yill577 23:47, 4 October 2006 (UTC)
In this case the full formula is ${\displaystyle R\to \alpha '/R}$, where ${\displaystyle \alpha '}$ is a constant appearing in string theory with the dimensions of mass-2, or equivalently length2. Usually, since ${\displaystyle \alpha '}$ pops up so often, people just leave it out of the equations and set it to some convenient value -- like "1" or "2." ${\displaystyle {\sqrt {\alpha '}}}$ is probably near the Planck length, so another way of interpreting the formula is that T-duality takes a circle that is R Planck lengths in radius to one which is 1/R Planck lengths in radius. Wesino 11:25, 6 December 2006 (UTC)

My background isn't in physics so I appreciate my basic ignorance, but every time I encounter m-theory I wonder, "So, what is our universe's brane?" Is it "now?" My understanding has been that "now" is basically just a coincidence, less and less causally connected as events' connections and shared causes diminish and become more distal. If that is true, then what is our brane?PMELD5 (talk) 03:26, 4 February 2008 (UTC)

It is not a simple thing, like the concept "now". It is possible to ask questions that simply don't make sense. A proper question must be framed in a way that contains most of the answer, at least for context. For example, the question "is an orange brachulus bisentient" simply makes no sense. In your case, "what is our brane" has several problems. One is that a brane has no intuitive, commonsense, or simple meaning--it actually is a fairly complex mathematical structure, a non-intuitive way for us to view the basic structure of our universe. Another is that "our brane" doesn't define "our"--it implies that there are many branes, and that they can belong to various entities. That, too, makes no sense in terms of actual M-theory as presented here. I doubt that there could possibly exist an answer that would satisfy you. In many areas of advanced knowledge, you really do have to learn and understand in order to speak intelligently about it, or even to ask a question. That observation probably applies at least somewhat to this, my comment, too. It is valuable to be humble and realize that it's okay that the world is full of facts and theories that we cannot understand without specialized training. David Spector (talk) 15:26, 20 January 2015 (UTC)
I don't agree with the above, but first things first: If we agree to use meters as units of R, then 1/R space has units of reciprocal meters, m-1. Now, while its probably true (IS true, as far as I can see) that to speak intelligently about many areas of knowledge or to ask "good" questions as judged by "the experts", you need to learn the subject to some level of detail, what I don't agree with is the implication that only 'expert' questions can be "good" (or only precise technical questions are good ones). Our brane is (theoretically) our past, present, and future. Not to blow you off, but some questions require an enormous amount of time to clearly answer. Since its unlikely that such an answer will be appreciated by the OP, few (who can sensibly answer) will bother. The (most reasonable) assumption is that if the OP actually wanted to understand the topic, s/he would have done the work (take a couple of hours to read, take days or weeks to understand, I'd guess). The topics which the OP could inform themself is "simultaneity" (or its lack of useful general meaning) and General Relativity. I refer those interested there. — Preceding unsigned comment added by 173.189.76.88 (talk) 19:41, 15 August 2015 (UTC)

## Wikibooks

Shouldn't this be moved to wikibooks? Just wondering. J. D. Redding 05:27, 16 April 2008 (UTC)

Not moved, because M-theory is central in modern physics, and there's a strong consensus that important things need to have articles about them in WP...no matter how opaque. But it is always a reasonable question where parts of an article play only a supporting role, and these can always be moved to Wikibooks. I prefer direct links to and from the supporting material, rather than that vague "extra material can be found at Wikibooks" graphic. - Dan Dank55 (talk)(mistakes) 04:02, 27 June 2008 (UTC)

## Timeline

"In the 1980s, a new mathematical model of theoretical physics called string theory emerged." The theory is in fact older. But in the 80s it (or what was known about the theory at this time) was proven to be free of anomalies and thus suddenly became "the real deal". —Preceding unsigned comment added by 82.113.106.155 (talk) 03:33, 1 April 2009 (UTC)

## First reference out of date

The link for the first reference is broken (The Mother of All Superstrings). I don't know the community guidelines for indicating this on the main page. —Preceding unsigned comment added by Drunkpotato (talkcontribs) 16:13, 15 September 2009 (UTC)

Thanks, fixed --ojs (talk) 20:58, 30 July 2011 (UTC)

## Strings or Membranes Vibrate?

The last sentence in the Background section reads:

"It did this by asserting that strings are really 1-dimensional slices of a 2-dimensional membrane vibrating in 11-dimensional space."

In this construction, just what is vibrating is ambiguous. Are they the 1-dimensional slices that are vibrating in 11-dimensional space? Or is it the 2-dimensional membrane?

Clarification is needed. Layman that I am, I interpret that it is the slices that vibrate. In this case I suggest as a possible revision:

"It did this by asserting that strings really are 1-dimensional slices of 2-dimensional membranes, and these strings vibrate in 11-dimensional space."

--WorldWideJuan (talk) 04:21, 28 July 2013 (UTC)

## 10 or 11?

This article states that string theory originally postulated 10 dimensions, but "This was later increased to 11 dimensions ..." But M-Theory states that "In string theory, spacetime is ten-dimensional, while in M-theory it is eleven-dimensional." Ecphora (talk) 12:00, 24 September 2014 (UTC)

The dimensionality is not firmly established. One of the problems is the holographic principle (where higher dimensionality can have an EXACTLY equivalent lower dimensional expression.173.189.76.88 (talk) 19:47, 15 August 2015 (UTC)

## Background is RUBBISH.

The Background section is so flawed that it has either been vandalized or written incompetently.
"Beginning in the 1960s, other subatomic particles were discovered." Muons were discovered in 1936, kaon and pion in 1947.

 Next sentence:"In the 1970s, it was discovered that protons and neutrons (and other hadrons) are themselves made up of smaller particles called quarks." Internal structure for these particles was observed in 1968 (and many if not most physicists believed the internal structure likely to be quarks).
Quantum Theory is used from the sub-atomic scale, up to the macroscopic scale (eg superfluidity can't be explained without it). The claim that Quantum Theory is " is the set of rules that describes the interactions of these particles." is at best so incomplete as to be misleading.


As a previous post points out, string theory did NOT "emerge" "in the 1980's". Supersymmetric String Theory had (arguably) its orgins in 1971 with the inclusion of supersymmetry into string theory in order to include fermions into bosonic string theory. A CRITICAL date is 1984 when solutions to fatal flaws of the previous theory were established, from this point forward, Supersymmetric String Theory could be reasonably described as "main stream" physics.


"Further, string theory suggested that the universe is made up of multiple dimensions." What GARBAGE! The existence of 3 dimensions of space and 1 of time has been known from time immemorial. String theory REQUIRED many more dimensions than the 4 of General Relativity.
"Furthermore, all these theories appeared to be correct." Correct?? More rubbish! There has been no experimental confirmation of SSST!! The theories all appeared to be equally consistent, but last I heard, none of them are able to predict any consequence which is measurable/observable. The difference between consistent with the facts and the correct explanation of the facts is the difference between most conspiracy theories and history. Also: "seemingly contradictory" is more rubbish. The 5 'flavors' of SSST were not "contradicory" but created AMBIGUITY and the possibility of multiple (or contradictory) interpretation.
They proposed a unifying theory called "M-theory", in which the "M" is not specifically defined, but is generally understood to stand for "membrane". But this from the History of String Theory article:"According to Witten himself, as quoted in the PBS documentary based on Brian Greene's The Elegant Universe, the "M" in M-theory stands for "magic, mystery, or matrix according to taste." I fail to understand the lack of basic comprehension which would lead one to think "M-theory" requires the "M" to be defined. M is not an abbreviation here. It is part of a noun. What is the "definition" of G in "General Relativity"?? Wow. The CLAIM that M is understood to derive from (or "stand for") Membrane REQUIRES a reference. As does any claim that Witten's statement is not definitive on the subject.
Taken as a whole, the entire section is fatally flawed and should be removed until it can be written based on the facts rather than fiction.173.189.76.88 (talk) 20:59, 15 August 2015 (UTC)

## Copying?

Here is a passage in The Real M-Theory by Md Santo:

In string theory, the fundamental objects that give rise to elementary particles are the one-dimensional strings. Although the physical phenomena described by M-theory are still poorly understood, physicists know that the theory describes two- and five-dimensional branes.

Here is a passage that User:67.4.254.227 added to this Wikipedia article earlier today:

In string theory, the fundamental objects that give rise to elementary particles are the one-dimensional strings. Although the physical phenomena described by M-theory are still poorly understood, physicists know that the theory describes two- and five-dimensional branes.

I undid this and hope 67.4.254.227 will explain the similarity before re-inserting. Peter Gulutzan (talk) 15:16, 16 December 2015 (UTC)

## Assessment comment

The comment(s) below were originally left at Talk:Introduction to M-theory/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

 Needs references even though it is just a simplification Snailwalker | talk 00:11, 21 October 2006 (UTC)

Substituted at 01:12, 22 May 2016 (UTC)

I find the repeated overuse of the word "elegant" in this article to be too subjective. I even saw a video where Woit said he did not find it elegant. Reading the strict definition of elegant, I personally do not think it qualifies. I would at least say "some string theorists describe it as elegant". I don't believe something is elegant by comparison to other theories which are also not elegant. For example Maxwells equations to me are more elegant, and in fact predict so much. M-theory predicts that its name has to be justified in the future. I may try to remove some of this overuse if there is agreement. — Preceding unsigned comment added by 99.203.11.60 (talk) 11:11, 16 March 2018 (UTC)

Woit is a "Senior Lecturer in the Mathematics department at Columbia University", IMHO he is not an WP:RS on physics. We would need some stronger sources to dispute that string theory is considered elegant. Rolf H Nelson (talk) 05:37, 19 March 2018 (UTC)

## Kudos

I thought I should pass along a warm fuzzy for the quality of this article. Too often, our introductory articles are poorly tended to and treated as second-class citizens. Wikipedia seems to struggle with its primary technical articles, and it can reasonably be argued that the mathematicians on Wikipedia are overly keen to dump a wheelbarrow of formulas quite early in articles.

This article should serve as a paradigm on how to do “Introductory” right. Greg L (talk) 16:07, 17 March 2018 (UTC)

## Simple English

Wikipedia has a simple English wiki, wouldn't it make more sense just to slap this in there as the "translation" of the main article? puggo (talk) 01:07, 3 April 2019 (UTC)

We actually have a few of these. See Category:Introductory articles. I agree that Simple English Wiki may be a better home for them but they're so established here by now that getting rid of them would be an inconvenience. StrexcorpEmployee (talk) 02:06, 29 December 2021 (UTC)

## String theorist on the roof?

What did Albert Einstein think of the string theory? He was a technically accomplished violinist after all. Well, he died two decades before M-theory, but what would have he thought about it? He spent the rest of his life trying to develop relativity into a "theory of everything" but lost to QM. Is string theory a victory for him or another defeat? 78.131.76.15 (talk) 18:41, 20 January 2023 (UTC)