Introduction to M-theory: Difference between revisions

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However, for string theory to be mathematically consistent, the strings must be in a universe of ten [[dimension]]s. This opposes our perception of the universe to have four dimensions: three space dimensions (height, width, and length) and one time dimension. String theorists explained the fact that only 4 dimensions are perceived, as opposed to ten, by saying that the extra six dimensions were "curled up" to be so small that they could not be observed day-to-day. The technical term for this is ''[[Compactification (physics)|compactification]].'' Physicists speculated that the compactified dimensions took the shape of mathematical objects called [[Calabi–Yau manifold]]s.

String theory as described above ran into a problem: another version of the equations was discovered, then another, and then another. Eventually, five major string theories were developed. The main differences between the theories were principally the number of dimensions in which the strings developed, and their characteristics (some were open loops, some were closed loops, etc.). Furthermore, all these theories appeared to be workable. Scientists were not comfortable with five seemingly contradictory sets of equations to describe the same thing.

Speaking at the string theory conference at the University of Southern California in 1995, [[Edward Witten]] of the [[Institute for Advanced Study]] [[second superstring revolution|suggested that]] the five different versions of string theory might be describing the same thing seen from different perspectives.<ref>{{Cite web |url=http://physics.usc.edu/Strings95/program.html |title=University of Southern California, Los Angeles, Future Perspectives in String Theory, March 13-18, 1995, E. Witten: Some problems of strong and weak coupling |access-date=2017-04-08 |archive-date=2020-11-15 |archive-url=https://web.archive.org/web/20201115210233/http://physics.usc.edu/Strings95/program.html |url-status=live }}</ref> He proposed a unifying theory called "[[M-theory]]", which brought all of the string theories together. It did this by asserting that strings are really one-dimensional slices of a two-dimensional membrane vibrating in 11-dimensional [[spacetime]]. According to Witten, the ''M'' could stand for "magic", "mystery", "matrix", or "membrane" according to taste, and the true meaning of the title should be decided when a better understanding of the theory is discovered.<ref>{{cite journal |last=Duff |first=Michael |date=1996 |author-link=Michael Duff (physicist) |title=M-theory (the theory formerly known as strings) |journal=International Journal of Modern Physics A |volume=11 |issue=32 |pages=6523–41 |bibcode=1996IJMPA..11.5623D |doi=10.1142/S0217751X96002583 |arxiv = hep-th/9608117 |s2cid=17432791 }}</ref>