
20221012: The REAL Possibility of Mapping Alien Planets!
 06:05: ... telescope is sent to do the work. The second is the string of pearls option, in which many socalled smallsats are sent in a ...
 10:07: ... the Sun. Remember that the scientists called this a string of pearls. That first cluster of craft was the first pearl. ...


20220921: Science of the James Webb Telescope Explained!
 13:29: Robin Saunders reminds us that there’s a relationship between gluon flux tubes and string theory.
 13:37: ... string theory actually began as an attempt to understand QCD, before being ...
 13:46: And asks whether the methods of string theory are being brought back to understanding gluons again?
 13:56: The core mechanics of string theory were developed to describe the very stringy onedimensional gluon bonds between quarks, particularly in mesons.
 14:20: Quantum chromodynamics actually started to explain was going on, so it suplanted hadronic string theory.
 14:28: ... as Robin notes, one of the vibrational modes of these strings looked like the graviton, so the entire theory was shrunk in size by ...
 14:41: We explain everything in our string theory episodes.
 14:45: ... now, decades later, with string theory still failing to produce a slamdunk testable prediciton, people ...


20220622: Is Interstellar Travel Impossible?
 18:03: And we even have ideas for black holes in theories of quantum gravity  for example, the fuzzball of string theory, which we did an episode on.


20220615: Can Wormholes Solve The Black Hole Information Paradox?
 06:01: ... advanced form of this is AdS/CFT correspondence, a branch of string theory that reveals that a particular type of universe with ...
 06:54: ... using only general relativity and accepted quantum mechanics  no string theories attached. To be fair, these US teams, dubbed the ...
 07:24: ... tidal wave of math in these papers pulls ideas from string theory, holography, quantum field theory, and quantum ...
 11:25: ... had seen this equation. The island rule had already been derived in string theory. The researchers were surprised to find that ...


20220525: The Evolution of the Modern Milky Way Galaxy
 11:10: ... it pulls it back down. Like beating a drum or plucking a guitar string, the stars oscillate up and down in the galactic plane, making a ...


20220427: How the Higgs Mechanism Give Things Mass
 11:37: ... and we saw how this can lead to the creation of cosmic strings in a recent episode. But cosmic strings are the perhaps ...


20220308: Is the Proxima System Our Best Hope For Another Earth?
 13:02: Nonetheless, we’re focusing in on a relatively stringent set of requirements for this exoplanet to be able to support life.
 16:48: And the one on cosmic strings  topological defects that may span the length of the universe.
 18:27: OK, on to cosmic strings.
 18:33: When those cosmic strings radiate gravitational waves, how is the Higgs field supposed to smooth itself out?
 18:46: ... episode  the simple vortex of phase angles making a loop around the string  is the most simplistic version of this ...
 19:20: Or are cosmic strings the only indication of a change in phase angle?
 19:45: I don’t know how you’d do this besides observing a cosmic string, but I suspect there are ways.
 19:51: ... Scoot asks whether cosmic strings could explain the filaments and voids in the large scale distribution of ...
 20:03: So the answer is maybe to the first two  but only if cosmic strings influence the CMB.
 20:12: ... strings may have had sufficient density at extremely early times to leave an ...
 20:24: ... is defined by those density fluctuations, so in that sense cosmic strings could have influenced it  but not directly in the sense of cosmic ...
 20:38: ...  extremely unlikely  in our most accepted understanding of cosmic strings there aren’t anywhere near enough of them to account for dark ...


20220223: Are Cosmic Strings Cracks in the Universe?
 00:00: ... defects stretching across the sky. These are cosmic strings, and many physicists think that they have to exist, and that we can ...
 00:58: ... formed from topological defects in the quantum fields, aka cosmic strings. They have subatomic thickness but prodigious mass and they ...
 05:59: ... met. Our ice cube forms sheets, but our Higgs field formed strings. Remember that the vacuum decayed in a random direction ...
 07:33: ... around a central line. And that central line is our cosmic string. Other topological defects may be possible. For example, a ...
 08:50: ... horizon, potentially leading to dozens of cosmic strings in a network across the universe. Unlike the topological defects ...
 10:09: ... occurs, a pair of “kinks” is formed in each of the newly formed strings speed away from each other along the string at near ...
 12:19: ... give us the data that we need to find these. Now if we do find a cosmic string, there’s one other point of confusion we’d need to ...


20220210: The Nature of Space and Time AMA
 00:03: ... theories of the theme some of them try to answer this theory doesn't string theory assumes that this that the stage is there that the the space ...


20211220: What Happens If A Black Hole Hits Earth?
 14:10: ... as an explanation for dark matter, and the one on fuzzballs  the stringy theory version of the black ...
 16:33: ... the faller, it continues to exist  coded in the complexity of the string vibrations. It’s holographically projected into 2 spatial dimensions, ...
 17:55: ... could be tested. Actually, this might be the most testable prediction of string theory. There are simulations that suggest that the gravitational waves ...


20211210: 2021 End of Year AMA!
 00:02: ... let's see how about this one from laz the creator if i held the purse strings to an unlimited science budget what wild experiments or projects ...


20211117: Are Black Holes Actually Fuzzballs?
 00:13: But many physicists will tell you that the best way to fix broken physics is with string.
 00:18: String theory, in fact.
 00:20: ... in the black holes of string theory  fuzzballs  are perhaps even weirder than the regular type ...
 05:28: Black hole paradoxes may be solved by string theory.
 05:32: In string theory, black holes are not hairless at all  in fact all of those strings make them positively fuzzy.
 05:43: First a spot of string theory.
 05:52: ... string theory, all elementary particles are oscillations in 1dimensional ...
 06:01: ... String theory immediately solves the problem of the black hole singularity, ...
 06:17: It turns out that though, that string theory can make sense of the black hole event horizon also.
 06:22: ... 1996, when Andrew Strominger and Cumrun Vafa created a black hole using string theory  in theoryspace, not ...
 06:37: ... the microstates on the horizon the number of possible configurations of stringy structures  the 1D strings themselves and higherdimensional ...
 07:04: The infinitesimal strings and branes of string theory might be the analog of the molecules that store the entropy of our room full of air.
 07:13: ... it was a decisive step and it gave us a compelling reason to think that string theory might explain where the microstates of black holes ...
 07:53: For instance, the profile of the radiation emitted by the strings precisely matched that of traditional Hawking radiation.
 08:00: This was another stunning match to theory, and also a way for stringy black holes to leak out their information.
 08:06: ... pretty good, but I realize that I haven’t really told you what these stringy black holes look like, or how they form, or how structure can actually ...
 08:45: ... while he was exploring stringy black holes, Samir Mathur found that the strings that formed the black ...
 08:55: In fact, if you have a bunch of strings dense enough to form a black hole in general relativity, it wouldn’t actually collapse.
 09:02: Rather it would grow to produce an agglomerate of strings with the same radius as a classical black hole.
 09:09: ... at all, but rather a real surface that looks like a tangled nightmare of strings and branes, like the hairball coughed up from some hyperdimensional ...
 09:25: ... a fuzzball will see its constituents crushed into a soup of elementary strings. ...
 09:52: The ability for strings to maintain structure in this extreme gravity comes down to an effect specific to string theory called fractionation.
 10:02: ... tension of a string is inversely proportional to its length: tight rubber bands are ...
 10:10: ... in string theory, when you merge a large number of strings, the tension of the ...
 10:22: That means by crushing an enormous number of strings together, the resulting monstrosity can be stretched to enormous scales.
 10:30: The normally Plancklength strings can therefore pile up into fuzzballs with sizes ranging from kilometers to light years.
 11:07: But if you approach the fuzzball you start to see this surface of stringy material with a thickness of about a Planck length.
 11:35: ... a fuzzball is forming, all of the matter  now dissolved into stringy mess, is pushed up to the surface and the interior grid of spacetime is ...
 12:17: Now let’s try a stringtheoretic version.
 12:20: In string theory we have extra compact dimensions  spatial dimensions that are coiled up on the Planck scale so we can’t see them.
 13:00: ... emergence of fuzzballs in string theory radically changed our vision of what a black hole could be and ...


20211005: Why Magnetic Monopoles SHOULD Exist
 06:30: ... construction is called the “Dirac string”, and Dirac’s argument is that if the string part of the Dirac string is ...
 06:43: The second part of the argument is under what conditions that string is undetectable.
 06:57: Imagine a charged particle  say an electron  passing by a Dirac string.
 07:02: To plot that trajectory you add up all possible paths of the electron, including paths to the left and to the right at the string.
 07:09: ... presence of the string, with its magnetic fields, should introduce different phase shifts ...
 07:22: In other words, the string would be detectable.
 07:24: But there’s one scenario where the string can never be detected.
 07:34: ... that charge, the phase shift induced between the different sides of the string is exactly one wave cycle  which means no observable ...
 07:42: ... for the Dirac string to be undetectable then electric charge can only exist in integer ...
 07:56: ... the upshot is that the string connecting monopoles is fundamentally unobservable, and Dirac argued ...
 17:56: Physicists hope to understand these things someday, perhaps with twistor or string theory.


20210511: How To Know If It's Aliens
 18:32: ... hurt to check. I like this a lot. Looking for dark matter in, say, string theory, before you check whether it’s black holes is like looking for ...


20210217: Gravitational Wave Background Discovered?
 00:00: ... gravitational waves and there are theoretical sources also cosmic strings topological seams in the fabric of space would produce waves when their ...


20210112: What Happens During a Quantum Jump?
 05:10: He argued that the same emission spectra could be got by thinking of these levels as fundamental vibrational modes, like on a drum or guitar string.


20201005: Venus May Have Life!
 13:48: And, ultimately, to ally with them in war against the cosmic string entities in the heart of the Sun that we discussed recently.


20200928: Solving Quantum Cryptography
 09:52: Suppose Alice wants to send a message to Bob—”CAT” which is represented by the binary string 1 1 0 1.
 14:24: Last week we talked about a highly speculative idea  lifeforms inside stars, formed from cosmic strings and magnetic monopoles.


20200921: Could Life Evolve Inside Stars?
 00:16: Oh, and here’s an extra crazy one  life composed of cosmic strings and magnetic monopoles, evolving in the hearts of stars.
 01:03: ... fundamental kinks and defects in the fabric of the universe  cosmic strings beaded with magnetic monopoles  may evolve into complex structures, and ...
 01:28: What exactly are cosmic strings and magnetic monopoles?
 01:38: Cosmic strings and magnetic monopoles are what we call topological defects.
 03:56: A 1D topological defect is a cosmic string  an extremely thin filament.
 04:10: We’re interested in the strings and monopoles for now.
 04:14: In certain theoretical scenarios, a monopole can be connected to the end of a string  or two strings, actually.
 05:31: Can these stringmonopole necklaces store information?
 06:29: With semipoles, it’s possible to form string segments capped by NONannihilating semipole pairs that actually repel each other.
 06:36: In this way, it may be possible to develop complex string structures, analogous to chemistry.
 07:00: Others have speculated that cosmic strings may get trapped inside stars in the process of star formation.
 09:50: ... going to have to get a much better understanding of cosmic strings and monopoles  and, you know, actually verify that they exist in the ...
 11:28: ... those who don't know, James is a higher being composed of cosmic strings and monopoles, visiting Earth from the core of the Sun to help spread ...


20200908: The Truth About Beauty in Physics
 00:37: ... it’s also been argued that modern theoretical physics, and in particular string theory, has been overly transfixed by the allure of beauty for decades, ...
 10:44: So now we come to string theory.
 10:46: The first compellingly beautiful aspect of string theory is that gravity, in the form of the Einstein field equations  automatically emerged from it.
 10:54: But there are other things too  for example, disparate versions of string theory seem to miraculously converge into one master theory.
 11:05: String theorists find their math beautiful, even if it is far from being simple.
 11:15: So did string theory fall for the same sort of misguided obsession with beauty as did Weyl?
 12:11: And so perhaps the mathematical wonders of string theory DO reflect something true about reality, but we’re struggling with how to interpret it all.


20200810: Theory of Everything Controversies: Livestream
 00:00: ... today from loop quantum gravity which is one of the founders to string theory to the foundations of quantum mechanics and the philosophy of ...


20200728: What is a Theory of Everything: Livestream
 00:00: ... physicist with really a hugely broad range of interests including string theory and loop quantum gravity in principle we could do this entire ...


20200708: Does Antimatter Explain Why There's Something Rather Than Nothing?
 04:48: ... So, if there exists some underlying more fundamental theory, maybe string theory for example, then CPT symmetry may no longer be a foregone ...


20200527: Does Gravity Require Extra Dimensions?
 05:57: ... most famous example of compactified extra dimensions is in string theory, and in modern superstring theory there are 6 additional spatial ...
 06:10: ... the idea of compact extra dimensions is much older than string theory  first proposed by Oscar Klein in the 1920s as part of what ...
 11:32: ... near being able to probe the sizescale of the extra dimensions from string theory though, and so string theorists can keep on ...
 13:29: ... black hole  regions like the Carter time machine and the infinite string of parallel ...
 15:33: ... the string of universes through the rotating Kerr black hole requires the ...
 15:44: ... Polygondwanaland: in reality, impossibleseeming things like an infinite string of universes or a time machine indicate that the math may have led our ...


20200511: How Luminiferous Aether Led to Relativity
 03:25: ... a wave on a string: each string segment moves up and down only, tugging on neighboring ...


20200428: Space Time Livestream: Ask Matt Anything
 00:00: ... stuff as well I was certainly dreaming about quantum with gravity and string theory when we were writing those episodes so so it varies massively ...


20200203: Are there Infinite Versions of You?
 11:39: ... duplicate region of the universe where Shakespeare’s plays are just long strings of S’s underscored with fecal smears  and where the infinite monkey ...


20200127: Hacking the Nature of Reality
 11:24: Other physicists quickly realised that it was telling us that mesons could be described by a very particular type physical system: a vibrating string.
 11:35: ... so string theory was born  at first as a description of strong nuclear force ...


20191217: Do Black Holes Create New Universes?
 04:27: Perhaps the configuration of the geometry string theory’s extra dimensions gets shifted  this would do the job.


20191209: The Doomsday Argument
 01:57: ... number of theories in physics from string theory to eternal inflation predict that the cosmological constant could ...
 12:57: ... a special thanks we pulled a few strings and got you moved over to the doomnever box . If anyone wishes to join ...


20191111: Does Life Need a Multiverse to Exist?
 11:24: ... example we have string theory: this candidate theory of everything suggests that the values of ...


20191104: Why We Might Be Alone in the Universe
 12:30: A few of you wondered if there's a connection between the loops of loop quantum gravity and the closed strings of string theory.
 12:39: The strings of string theory have a somewhat physical interpretation  the fact that they can hold energy and vibrate and exist in space.


20191015: Loop Quantum Gravity Explained
 00:06: And can it really defeat string theory in our quest for a Theory of Everything?
 00:32: ... it quite a bit already, including what’s probably the lead contender  string ...
 00:42: But string theory isn’t the only game in town  or so some physicists believe.
 00:47: ... gravity that avoids a lot of conceptual baggage like tiny wiggling strings made of coiled up extra ...
 02:54: In string theory, a type of background independence emerges in an abstract space of moving strings and with that comes a gravitational field.
 03:04: But for that to work first you need those strings to exist  and we don’t know if they do.
 03:10: ... quantum gravity tries to quantize general relativity with no strings attached, while preserving the background independence already inherent ...
 11:13: And without adding big assumptions – like the existence of strings or extra dimensions or supersymmetry.
 13:16: Loop quantum gravity is an intriguing alternative to the more popular string theory.


20191007: Black Hole Harmonics
 03:02: ... or a black hole – are analogous to the harmonics of a vibrating guitar string or piano ...
 03:12: In the latter cases we can describe a vibrating string as a series of standing sine waves of different frequencies, all happening at the same time.
 03:22: ... lowest frequency the string can support is called the fundamental mode – it’s usually the strongest ...
 03:40: The full set of possible frequencies a string can support are called its harmonics.


20190930: How Many Universes Are There?
 07:20: People have also invoked the anthropic principle plus eternal inflation to explain a conundrum in string theory.
 07:27: ... we’ve talked about before, modern string theory is difficult to pin down because there are countless possible ...
 07:46: The vast space of possible configurations of these compact dimensions is referred to as the string landscape.
 08:01: We don’t know why our universe has the particular string vacuum state that it does.
 08:14: Enter the anthropic principle once again: eternal inflation gives us enough universes to easily populate the entire string landscape.


20190819: What Happened Before the Big Bang?
 06:04: As well as theories which also unify gravity, like string theory.
 10:04: ... are also deep possible connections between inflation and string theory and with the holographic principle, as described in one of ...


20190718: Did Time Start at the Big Bang?
 09:52: ... there isn't anywhere near enough matter to do that unless we bring in string theory the SteinhardtTurok model suggests that our universe floats in a ...


20190509: Why Quantum Computing Requires Quantum Cryptography
 07:43: ... generates a random string of bits, 0’s and 1’s and encodes these bits using photons polarized in a ...


20190410: The Holographic Universe Explained
 01:02: We’ve moved from quantum field theory to black hole thermodynamics to string theory.
 04:06: ... laid out the first steps towards how this could be achieved using string theory, but ultimately it was Juan Maldacena who figured out a concrete ...
 04:26: Let’s ignore string theory for the moment and just think about how to create an extra dimension.
 05:53: We also see it in string theory, which I’ll come back to.
 07:42: But for the details we need string theory.
 07:47: Even from the beginning string theory had hints of this scale invariance and dimensional weirdness.
 07:54: ... quarks – mesons – as this strand of gluons that behaves like a vibrating string. ...
 08:15: That means you can pretend string lengthslashenergy is a separate dimension as a calculation trick.
 08:44: This and other glitches led to string theory being abandoned as a model for the strong force.
 08:49: ... to make it a theory of quantum gravity, and the scale invariance of the strings becoming a central feature of string ...
 09:02: We now have a several versions string theory that try to explain how vibrating strings can lead to the familiar particles of this universe.
 09:10: These were tentatively united by Ed Witten’s Mtheory, which showed that different types of string and string theories were all related by dualities.
 09:27: These arose from the way string size and energy scales could be rescaled.
 09:34: But the strangest string duality was still to come with AdS/CFT correspondence, proposed by Argentinean physicist Juan Maldecena in 1997.
 09:52: Maldecena imagined a set of string theory objects called branes.
 09:57: These are like multidimensional strings that can serve as start and end points for strings, but also as spaces embedded within higherdimensions.
 10:15: The strings connected to these branes are scale invariant, so their length and energy can vary without changing the physics.
 10:57: This quality fcame from the energyscaleinvariance of the strings embedded in the construction of this space.
 11:04: In good stringtheorist style, Maldacena defined incorporated that scale factor into be a new spatial dimension.
 11:38: As with the other dualities in string theory, this one was extremely useful for calculations.
 15:28: ... AdS/CFT correspondence, the volume exhibits gravity via a type of string theory, while the surface exhibits no gravity  only a quantum field ...


20190403: The Edge of an Infinite Universe
 14:20: That structure looked exactly like a string theory with gravity and everything.


20190116: Our Antimatter, Mirrored, TimeReversed Universe
 13:52: ... inverted version of Canada. The last episode before the break was, "Why string theory is Wrong". Today, I want to address the comments to that episode ...
 15:29: ... if it provides an answer to the hierarchy problem and gives us super string theory it will be odd if supersymmetry existed as part of super string ...
 16:06: ... other point is that the large undefined parameter space of string theory  the so called 'String landscape' is no more of a problem for ...
 16:49: ... or wrongness. FieldStrength's final point is that the untestability of string theory is connected to the extreme energy scale of quantum gravity and ...
 17:15: ... yeah string theory is apparently not yet testable, but I disagree with those who say ...


20190109: Are Dark Matter And Dark Energy The Same?
 12:07: Which is good for string theorists, as Farnes notes, but not for observers because that’s not consistent with what we see.


20181220: Why String Theory is Wrong
 00:13: String theory is certainly beautiful in the eyes of many physicists, but is it beautiful enough to pursue even if it's wrong?
 01:03: Could this also be the case with string theory?
 01:06: ... idea did work when translated to the very particular case of a quantum string, which is part of what got string theory going in the first ...
 01:18: We talked about this in detail in our episode on why string theory is right.
 01:23: Which itself was a sequel to our primer on the basics of string theory.
 01:27: In those episodes, we saw some of the remarkable ways that string theory promised to converge on a theory of everything.
 01:35: ... under one umbrella, and there's also the convergence of many versions of string theory into a single picture with a very specific number of extra ...
 01:55: ... of this promise of being so right do more and more physicists think that string theory is after all either woefully incomplete or just plain ...
 02:07: Modern string theory is the convergence of many beautiful ideas in physics, each of which feel right in their own way.
 02:14: ... see where string theory ultimately fails, we need to rewind to look at some of these a ...
 04:57: These may have seemed like fatal flaws, but we can thank this wrongness for the later development of string theory.
 05:07: For example, adding more compact dimensions of various shapes and, of course, strings.
 05:16: String theory is just the most famous.
 05:18: So, start with KaluzaKlein, add vibrating strings and exactly the right extra special dimensions, and you have string theory.
 05:40: It also introduces fermions to the boson only version of string theory to give super string theory.
 06:03: Superstring started out with incredible promise, and so there was a proliferation of different versions of super string theory.
 06:20: Five different approaches to getting all of the desired particles out of the basic premise of strings wiggling in ten dimensions.
 06:32: What differs is the detailed geometries and symmetries of those spaces, and the way strings vibrate within them.
 07:12: These dualities reveal that certain classes of string theory were actually the different ways of expressing exactly the same theory.
 07:20: Perhaps there was a glimmer of hope for these divergent versions of string theory after all.
 07:50: Our tiny quantum strings can roam that small dimension.
 08:01: ... number of times a string winds around this compactified dimension is called its winding number. ...
 08:17: These strings are vibrating with standing waves like guitar strings, and their energy also depends on the frequency of that vibration.
 08:25: That frequency depends on the density of wave cycles on the string.
 08:30: ... divided by the radius. So, there are two ways to get a highenergy string: have a large winding number along with a large radius that gives you a ...
 08:55: ... radius can be used to define the momentum of a particle produced by this string. ...
 09:19: ... sounds weird but this may just have saved string theory. I just described a type of duality, in this case tduality, ...
 09:48: Tdualities prove that some of these different versions of string theory are actually different expressions of the same theory.
 09:54: The other main type of duality in string theory is sduality, strongweak duality.
 09:59: In this case it's a duality between strongly versus weakly interacting strings. This seems even more contradictory, but it's incredibly powerful.
 10:18: Sduality provided the final linchpin that demonstrated that the five different types of string theory were all manifestations of the same theory.
 10:31: ... a string conference in '95, Witten showed that the disparate string theories were ...
 10:51: ... that it adds a single extra dimension, to connect all of the five super string theory types via ...
 11:41: See, in parallel to the development of super string theory, other physicists have been working on super gravity.
 11:49: ... Super gravity should be the low energy, largescale limit to super string theory. So it was incredibly exciting that string theory appeared to ...
 12:14: ... with each other and with super gravity restored the sense of beauty to string theory. It appeared to be on the track to rightness once again, so So ...
 12:53: The behavior of strings in these hyper dimensional surfaces is only understood in idealized cases.
 13:08: ... 500 different topologies, the actual number is a lot higher. This is the string landscape. Each geometry for the compactified dimensions implies a ...
 13:44: ... principle the standard model lives somewhere in the string landscape, but without knowing the geometry of the extra dimensions, ...
 14:00: Essentially all string theories require supersymmetry in order to work.
 14:16: But string theories are still rightly concerned. Their elegant theory which was converging so beautifully has stalled.
 14:55: So perhaps string theorists should also stick to their guns.
 15:00: ... wrong or incomplete as current string theory may be, it may also be the inevitable early step as we seek an ...
 15:14: ... the physics required to understand string theory is tough thankfully there are online tools that can help like ...


20181212: Quantum Physics in a Mirror Universe
 00:02: ... to seem heavily and yeah we'll be covering that after we do why string theory is wrong because you guys haven't stopped complaining that it ...


20181121: 'Oumuamua Is Not Aliens
 15:28: Well, actually, modern string theory relies on supersymmetry so it's already included.
 15:37: Actually, the name string theory originally applied to what we call bosonic string theory.
 15:53: And these days some form of superstring theory is implied when people talk about string theory.


20181114: Supersymmetric Particle Found?
 02:08: It's a key feature in some grand unified theories as well as modern string theory, leveling it up to superstring theory.
 12:33: ... below to subscribe to "Two Cents." Last week, we talked about why string theory is so compelling to so many ...
 12:51: Many of you have some interestingly passionate hate for string theory on the grounds that it's so far proved unfalsifiable.
 13:04: String theory may be wrong, but it's not testable due to the limits of current facilities.
 13:25: The thing that makes string theory less sciencey is that its modern version, Mtheory, is not particularly welldefined.
 13:39: String theory is not precise enough yet to be confirmed wrong, which means it might be right or not.
 14:17: To quote, "I thought one of the fundamental properties of the strings was that the maths only works if they are one dimensional.
 14:24: So how can you get world sheets?" Yes, it is a pain keeping the number of dimensions straight in string theory.
 14:32: ... dimension of space and one of time, this is the shape traced out by a string moving through ...
 14:47: So yeah, the math of string theory only works for 1D objects because these trace 2D world sheets.
 15:32: But this has no bearing on the compactified extra dimensions of string theory.
 16:06: And to end on a funny, Dash to the Max points out that string theory is literally like playing a sad song on the world's smallest violin.
 16:16: And if it proves wrong in the end, at least we have the perfect instrument for a requiem to string theory.


20181107: Why String Theory is Right
 00:06: ... see string theory as the one great hope for a theory of everything that will unify ...
 00:20: Others see string theory as a catastrophic dead end, one that has consumed a generation of geniuses with nothing to show for it.
 00:29: So why are some of the most brilliant physicists of the past 30plus years so sure that string theory is right?
 00:37: [MUSIC PLAYING] Why has string theory been the obsession of a generation of theoretical physicists?
 00:48: What exactly is so compelling about tiny vibrating strings?
 00:53: In our last stringtheory episode, I talked about what these things really are and covered some history.
 00:59: ... short, the strings of string theory are literal strands and loops that vibrate with ...
 01:14: And, by the way, these strings exist in six compact spatial dimensions on top of the familiar three.
 01:21: In this episode, I'm going tell you why string theory is right, at least why so many of those geniuses think it is.
 01:52: I also want to give you a teaser on why string theory is actually wrong.
 02:01: The greatest criticism of string theory is that it's never made a testable prediction.
 02:06: ... space of possible versions of string theory is so vast that nothing can be calculated with certainty, so ...
 02:19: But string theorists might disagree.
 02:22: They might say, maybe half jokingly, that string theory does make one great prediction.
 02:41: But the fact is when you start to work out the math of string theory, gravity appears like magic.
 02:47: You don't need to try to fight gravity into string theory.
 02:50: ... fact, it will be difficult to remove it, and the quantum gravity of string theory is immune to the main difficulty in uniting general relativity ...
 03:07: ... in a recent episode, but before we get to the nuts and bolts of how string theory predicts gravity, it's worth taking a moment to see how stringy ...
 04:22: OK, let's switch to string theory where particles are not points.
 04:32: When strings move on a spacetime diagram, they trace out sheets or columns.
 04:37: In fact, you can think of a string not as a 1D surface but as a 2D sheet called a world sheet.
 04:45: Now let's look at the interaction of two strings.
 04:53: Even the most energetic interactions are smeared out over the string, so you avoid the danger of black hole creating infinities.
 05:06: ... illustrate why quantum gravity isn't hopelessly broken in string theory, and that's a huge point in favor of string theory, but these ...
 05:20: And this is the second point in string theory's favor.
 05:22: ... see, it turns out that tiny vibrating quantum strings automatically reproduce the theory of general relativity and, in the ...
 05:39: This stuff appears a little too naturally in the math of string theory to be a coincidence, or so a string theorist might tell you.
 05:48: For some reason, vibrating strings are bizarrely well suited to quantization.
 07:17: Quantizing the motion of strings also starts out ugly, but there are also some math tricks to make it work.
 09:02: ... turns out that exploring a very different symmetry of string theory both makes it possible to quantize the theory and gives us a very ...
 09:14: So, like I was saying, when we try to quantize string theory, of course it's a huge mess.
 09:36: It says that changing the scale of space itself shouldn't affect the physics of strings.
 10:25: That's on the 2D dimensional world sheet of a quantum string.
 10:30: ... the 2D sheet traced out in spacetime by a vibrating 1D string has this symmetry that lets us redefine the scale on its surface however ...
 10:41: ... quantum wave equation from the equations of motion, but only for 1D strings making a 2D world sheet, not for any other dimensional ...
 10:57: This is part of what makes strings so compelling.
 11:28: So, with our quantized equations of motion in hand, you can predict the quantum oscillations of our string.
 11:44: ... you use string theory to write down the gravitational field in what we call the ...
 11:57: ... get the right particles, including the graviton and the photon, out of string theory for a very specific number of spatial dimensions, nine to be ...
 12:11: In fact, if string theory makes any predictions, it's the existence of exactly this number of extra dimensions.
 12:18: And this is where string theory starts to look less attractive.
 12:25: ... String theorists hypothesize that the extra dimensions are coiled on themselves ...
 12:43: And that's just the first of many problems of string theory.
 12:49: ... were lead to string theory by the elegance of the math and the fact that it appeared, at ...
 12:58: ... convergence is also seen in the union of different string theories by M theory and in the discovery of AdS/CFT correspondence ...
 13:26: Perhaps we're now overly distracted by the elegance of string theory.


20181025: Will We Ever Find Alien Life?
 08:46: ... Anchordoqui and collaborators found a less stringent limit on this likelihood by assuming that a lot of life gets wiped out ...
 13:18: Last week we dipped our toes into string theory.
 13:38: Add it to string theory and you get superstring theory.
 13:54: ... response to me saying that string theory has only one tunable parameter, Michael Murphy sarcastically ...
 14:04: ... he's referring to the number of calibrial manifolds that string theorists need to search through to find the geometry of our universe's ...
 14:30: Now, some string theorists would say that there are zero free parameters.
 14:43: Korbus Barkly and some others ask whether, if string theory makes no testable predictions, shouldn't it be just called string hypothesis?
 16:20: Does not the idea of "shut up and calculate" and "we don't care what strings are made of" sound a lot like the flaws that science finds in religion?
 17:25: He was struck by the potential of multidimensional Pringles to unify string theory.


20181018: What are the Strings in String Theory?
 00:07: You may have heard the usual pop psy description of string theory.
 00:10: There are these tiny vibrating strings, and that's where all the force's particles, including gravity, in the entire universe come from.
 00:18: This raises more questions than it answers, like why strings?
 01:20: That would be a theory of everything, and this is the great hope of string theory.
 01:26: In the following episodes, we're going to explore the gory details of string theory.
 01:32: But today it's String Theory 101.
 01:38: I mean, why tiny vibrating strings versus literally any other tiny vibrating anything?
 01:45: What exactly are the strings of string theory?
 01:48: First let's do a quick primer on the origins of string theory.
 02:09: ... suggested that the quarks in mesons are connected by you guessed it strings. ...
 02:23: In this case, the strings are stretched out tubes of strong nuclear force, vibrating elastic bands made of gluons.
 02:32: A lot of work went into figuring out a quantum theory for the strong interaction based on the physics of strings.
 02:46: ... of the reasons this strong force version of string theory got stuck is that it predicted the existence of unexpected and ...
 03:16: ... the type of particle produced by this little investigation into hadronic strings except that there's no way anything like the graviton should appear in ...
 03:51: In fact, what if all forcecarrying particles result from oscillations in tiny strings?
 03:58: ... we needed was to make the strings a bit smaller, like 20 orders of magnitude smaller, shrinking from the ...
 04:20: This was socalled Bosonic string theory.
 04:31: If wiggly strings can explain forcecarrying bosons, why not also the fermions that comprise matter?
 05:22: Let's talk strings.
 05:24: So wiggly strings could explain the whole universe.
 05:29: To understand quantum strings, first we need to look at regular strings.
 05:35: The key is that strings can carry waves.
 05:38: And if the string has ends or is tied in a loop, then a wave will end up overlapping with itself.
 05:57: Constructive interference only happens if the wavelength of the wave fits a neat number of times along the length of the string.
 06:14: The result is that for a given string, only certain frequencies corresponding to certain energies are possible.
 06:22: These resonant frequencies depend on the length of the string, also its tension, which defines wave velocity and so relates frequency to wavelength.
 06:31: For example, this leads to the specific frequencies of vibration on a guitar string.
 06:45: String theorists weren't the first to notice this.
 06:57: But quantum strings are much more ambitious than boring electron orbits.
 07:10: Particle mass just comes from the length of the string and its tension.
 07:17: String length defines mass, but also defines which complex vibrational modes are possible.
 07:29: So this is the great promise of string theory.
 07:32: ... defining a single parameter, the string tension, or equivalently, string length scale, all of the possible ...
 08:05: The strings are real physical strands, and the waves are wiggles in actual space.
 08:36: Most string theorists are more interested in what strings do, not what they're made of.
 08:51: These last properties are important because it gives a mechanism for the particles of string theory to interact and to decay into other particles.
 09:00: This picture of strings coming together jointly and splitting apart is a huge strength of the theory.
 09:31: String theory fixes this because the graviton is a loop, not a point particle.
 09:37: Its interactions are smeared around that string, handily avoiding the explosion of mathematical infinities you get below the Planck length.
 09:45: All this stuff sounds great, and by the way, doesn't work for any other geometrical structure other than a 1D string.
 09:54: So vibrating guitar strings, yes.
 10:01: ... the strings themselves are 1D, but to even start to produce the properties of known ...
 10:41: But this sort of thing doesn't deter string theorists.
 11:16: Very tiny objects like quantum strings could explore that extra dimension, and importantly, oscillate in it.
 11:30: Three large dimensions of space and six tiny PacMan dimensions that only strings experience.
 11:37: Voila, string theory is saved.
 11:54: ... theory unites different string theories because it demonstrates some philosophically fascinating ...
 12:13: The exact behavior of strings depends on the shape of their compact dimensions.
 12:19: In fact, the single free parameter in string theory becomes the configuration of the extra dimensions.
 12:25: Find the right location in this string landscape, and you perfectly describe the universe.
 12:43: Right now string theory appears to be at an impasse.
 12:53: Tuning that string landscape to match our universe is daunting and perhaps impossible.
 13:08: In coming episodes, we'll look deeper into both the successes, the failures, and the profound weirdnesses of string theory.
 13:17: And you can decide for yourself whether you accept the fundamental stringy nature of space time.


20181003: How to Detect Extra Dimensions
 06:15: They're used in string theory, where they typically have a large number of dimensions.
 06:20: But in string theory, all but three spatial dimensions of the brane are inaccessible.
 11:02: So string theorists are OK for now.
 13:02: And string theories are an example.


20180920: Quantum Gravity and the Hardest Problem in Physics
 12:08: That's exactly what string theory seeks to do.


20180905: The Black Hole Entropy Enigma
 11:24: You just need to add a little bit of string theory.
 11:34: It might also be true, and obviously we'll be back before too long to talk about string theory and the holographic nature of spacetime.


20180620: The Black Hole Information Paradox
 09:39: Leonard Susskind formalized this idea in the context of string theory in what we now know as the holographic principle.
 11:22: ... ideas about the nature of information and entropy, exploded the field of string theory, and hinted at the possible holographic nature of ...


20180418: Using Stars to See Gravitational Waves
 05:00: ... in which binary supermassive black holes were common, or from cosmic strings, if they ...


20180315: Hawking Radiation
 02:55: They can oscillate with different frequencies, much like the many possible vibrational modes on a guitar string.
 03:01: A particle is like a note on the string.
 03:32: One way that quantum fields are very different to guitar strings is they can have both positive and negative frequencies.


20171025: The Missing Mass Mystery
 13:17: Maybe we'll at least get some evidence for the string theory or something.


20171019: The Nature of Nothing
 08:51: ... the same way that an organ pipe or a guitar string of a particular length only resonates with waves of certain frequencies, ...


20170913: Neutron Stars Collide in New LIGO Signal?
 15:42: And Hot Fuzz is obviously a reference to black hole singularities in string theory.


20170712: Solving the Impossible in Quantum Field Theory
 04:09: ... equation you string together from this one diagram represents all of the ways that two ...


20170707: Feynman's Infinite Quantum Paths
 15:00: A few of you asked whether quantum field theory and string theory are the same thing.
 15:16: String theory states that all particles are different vibrational modes in onedimensional objects called strings.
 15:30: ... with stunning success and is the foundation of the standard model, string theory is untested and may have nothing to do with ...


20170628: The First Quantum Field Theory
 02:03: Anyone who's ever strummed or shredded knows that a stretched string vibrates with a certain frequency when plucked.
 02:22: ... any point in time, every point on a vibrating string is displaced by some distance from its relaxed or equilibrium position, ...
 02:38: Guitar strings are onedimensional, but we can expand the analogy to any number of dimensions.
 03:45: And let's go back to the string.
 03:47: If this were a quantum mechanical guitar string, then there'd be a minimum amplitude for the vibration that depended on its frequency.
 04:26: Everywhere in the universe, that value is usually zero, but just like the string or the air density field, it could oscillate.


20170607: Supervoids vs Colliding Universes!
 09:30: And it could happen frequently or rarely, depending on the completely unknown details of the string theory parameter space.


20170315: Time Crystals!
 04:28: So you prepare a string of ions where the line spins.


20170202: The Geometry of Causality
 05:15: ... from my stationary point of view, I define my xaxis as a long string of spacetime events at different distances, but that all occur ...
 12:07: ... out of the mathematical singularity at the center of black holes is with string theory, which proposes that particles that we see in regular 4D ...
 12:22: One idea is that the inside of an event horizon is composed of a ball of raw strings, a socalled fuzzball, and that no infinite density exists.


20161116: Strange Stars
 13:09: ... go through the black hole information paradox, Hawking radiation, some string theory, the holographic principle, other ...


20161012: Black Holes from the Dawn of Time
 03:21: For example, the collapse of cosmic string moves and the collision of bubble universes?


20160601: Is Quantum Tunneling Faster than Light?
 10:15: Throw in some string theory and black holes and a really unique writing style and it's a very insightful Pop Sci book.


20160302: What’s Wrong With the Big Bang Theory?
 04:31: ... together and what some of the resolutions might be [CLEARS THROAT] string theory another ...


20151216: The Higgs Mechanism Explained
 01:32: But now, add some energy to that field at a particular spot, and it's like plucking a guitar string.


20150923: Does Dark Matter BREAK Physics?
 06:58: Sinking down into the depths of quantum field and string theory, you can find all sorts of strange fish, WIMPs, axions, neutralinos.


20150819: Do Events Inside Black Holes Happen?
 00:24: That means no Hawking radiation, no string theory, and no quantum anything baby steps.


20150729: General Relativity & Curved Spacetime Explained!
 08:32: ... even when people are referring to relativity or string theory or whatever, it's just a lot easier to say the word gravity than ...


20150617: How to Signal Aliens
 09:13: ... has a balloon in it filled with helium that's attached to the floor by a string and I simultaneously drop the van off a cliff and cut the string ...


20150610: What Happens to a Helium Balloon in Freefall?
 00:26: Now, in that balloon video, there's a heliumfilled balloon attached by a string to the floor of a minivan.
 00:39: And at the same moment that I let go, I want to cut the string that holds the helium balloon to the floor.


20150603: Is Gravity An Illusion?
 04:51: That is the new vertical and the pendulum string and the balloon string are just aligning with the vertical the way they always do.
