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Message: <blockquote data-quote="freyar" data-source="post: 6678797" data-attributes="member: 40227">Pretty much the same as it's always been. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f61b.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=":p" title="Stick out tongue    :p"  data-smilie="7"data-shortname=":p" />More seriously, string theory starts out as studying the behavior of a quantum string moving in spacetime --- you can think of the string as something like a very tiny rubber band.  In quantum mechanics, the string can only vibrate in particular ways.  If you look at those vibrations closely, they look like certain types of particles, including photons (as you know, particles of light) and gravitons (hypothetical particles of gravitation).  Remarkably, if you study the motion of the string even more carefully, you can (among other things) derive Einstein's equations for gravity.  So, string theory predicts at least one thing: gravity!The advantage of string theory vs normal particle physics lies in the detailed math.  String theory is typically more complicated (more below, though), but it is complete.  With normal particle physics, we are typically forced to say that there's some energy level beyond which we have no knowledge, but string theory in principle can explain everything.  That's part of the appeal.  Of course, part of the complexity includes things like extra dimensions, etc, etc.  And most of the distinctively stringy effects are at such high energies we don't really have prospects for testing them, so string theory gets criticized a lot for that.  On the other hand, other theories of quantum gravity which are less mathematically rigorous also don't make unique predictions, so we just have to accept that if we want to think about quantum gravity at this point.  It's very hard for any quantum gravity theory to make currently testable predictions, and many of the predictions can be mimicked by more standard physics.So string theory is, in principle, a theory of all physics, including quantum gravity.  It is simple in its basics but extremely rich, and that richness comes along with complications (extra dimensions, for example, give us the chance to figure out where the Standard Model of particle physics comes from but at the cost of some very hairy math and a lot of other possibilities to choose from).  But string theory is also very important in other ways.  In 1997, Juan Maldacena made the startling discovery that string theory in certain spacetimes is actually the same thing as certain theories of normal particle physics which happen to be very similar to theories of the strong nuclear force, which are notoriously difficult to solve otherwise.  This has been extremely well tested and in fact provided the first remotely reasonable explanations for some results of the RHIC experiment (which smashes large nuclei together).  Many nuclear theorists have learned string theory for this reason.  In more recent years, this correspondence has been generalized to other theories, and some physicists are using string theory to try to understand problems in materials science, such as superconductivity.  So string theory is also very much another way to understand more normal theories of particle physics.</blockquote>

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