Science discussion, continued from other thread

[Kelly]

Is there any proof for string theory?

Since the LHC has failed to create its expected black holes, perhaps not yet. However, perhaps their energies are higher than those predicted, and they might find them in the future when higher energies are used.

Another method of detecting extra dimensions is described here:

South Pole Neutrino Detector Could Yield Evidences of String Theory

In part, it states:

Researchers at Northeastern University and the University of California, Irvine say that scientists might soon have evidence for extra dimensions and other exotic predictions of string theory. Early results from a neutrino detector at the South Pole, called AMANDA, show that ghostlike particles from space could serve as probes to a world beyond our familiar three dimensions, the research team says...

AMANDA, funded by the National Science Foundation, attempts to detect neutrinos raining down from above but also coming "up" through the Earth. Neutrinos are so weakly interacting that some can pass through the entire Earth unscathed. The total number of "down" and "up" neutrinos is uncertain; however, barring exotic effects, the relative detection rates are well known.

AMANDA detectors are positioned deep in the Antarctic ice. The NSF-funded IceCube has a similar design, only it has about six times more detectors covering a volume of one cubic kilometer. A neutrino smashing into atoms in the ice will emit a brief, telltale blue light; and using the detectors, scientists can determine the direction where the neutrino came from and its energy.

The key to the work presented here is that the scientists are comparing “down” to “up” detections and looking for discrepancies in the detection rate, evidence of an exotic effect predicted by new theories.

“String theory and other possibilities can distort the relative numbers of ‘down’ and ‘up’ neutrinos,” said Jonathan Feng. “For example, extra dimensions may cause neutrinos to create microscopic black holes, which instantly evaporate and create spectacular showers of particles in the Earth's atmosphere and in the Antarctic ice cap. This increases the number of ‘down’ neutrinos detected. At the same time, the creation of black holes causes ‘up’ neutrinos to be caught in the Earth's crust, reducing the number of 'up' neutrinos. The relative ‘up’ and ‘down’ rates provide evidence for distortions in neutrino properties that are predicted by new theories.”

[Kelly]

String Theory for Dummies

Not really for dummies, but for those without much graduate-level math experience.

There is a TV mini-series named NOVA - The Elegant Universe (2003) hosted by physicist Brian Greene and based on Greene's book by a similar name (The Elegant Universe : Superstrings, Hidden Dimensions, and the Quest for the Ultimate Theory). He describes the four fundamental forces, and after discussing gravity, ends up discussing String Theory. He includes M-Theory and the event where Witten proposed it. He also discussed branes and the concept of gravitons leaving our brane (and travelling between universes).

I have watched the show and really enjoyed it. It does do a good job of introducing on to the subject, and is rather entertaining.

You might also wish to read the book. And while at it, Greene has a new book, named The Fabric of the Cosmos: Space, Time, and the Texture of Reality. Again not requiring graduate-level math or physics. He continues with String Theory (and other things) and even touches on Loop Quantum Gravity (a subject that we really have not discussed yet).

My brother (an intelligent person but has no formal physics education) has both books and quite enjoyed them.

Of course, there indeed is a String Theory For Dummies and even The Complete Idiot's Guide to String Theory.

I do not know much about these books, though.

[cosmicbimbo]

In general the "Dummies" Series and "Complete Idiot's Guide" series are very good.

[daveb]

Thanks, Kelly. :) 've bookmarked those for possible future purchase.

I like Larry Gonick's Cartoon Guides to ... and he does have a physics one, but probably doesn't get much into more esoteric stuff like string theory, I'm guessing.

[Henny]

I like Larry Gonick's Cartoon Guides to ... and he does have a physics one, but probably doesn't get much into more esoteric stuff like string theory, I'm guessing.

I liked his "Cartoon History of the United States". It was very helpful.

[Kelly]

Loop Quantum Gravity (fer dummehz)

Again, not really for dummies, but also not requiring a science degree. Loop Quantum Gravity (LQG) is another contender for a possible Theory of Everything (TOE). In the early 20th Century, Relativity (which describes large-scale objects) and Quantum Mechanics (which describes behavior at very teeny sizes) were developed. Both work independently, but a theory of everything needs to show how both can work together, and to unify gravity with the other three forces.

String Theory predicts gravitons—spin 2 "particles" that have interesting features (such as being closed and not attached to our brane, or universe, and can actually travel between universes).

But Loop Quantum Gravity also addresses quantized gravity. Further, LQG does not require a universe in 11 dimensions. Also, as mentioned in http://newphysicsandthemind.net/9.html :

But string theories are background-dependent. The background is spacetime, and in string theories all of the forces—including gravity—operate against the background of spacetime. This seems to present a conceptual stumbling block in the way of using string theories to reconcile general relativity’s gravity with quantum physics’ other forces, because general relativity is a background-independent theory. Under general relativity, the force of gravity shapes spacetime—[it] is spacetime.

So it’s hard to see how a string theory road to quantum gravity can be the whole road: even if string theory’s models provide extraordinary accuracy to the proposed structures of physics’ forces and matter, background-dependent theories will not give us the gravitational exceptionalism that we need. Gravity is not like the other forces. The other forces operate against the spacetime backdrop, in a spacetime grid. Gravity doesn’t. Gravity is the spacetime grid.

Briefly, LQG quantizes space and time. Perhaps this is not a surprise—it seems natural to think that, since everything else is quantized, why not space and time? I had assumed that it was ever since I was rather young. So the concept itself seems obvious. But a workable theory is recent.

In short, from http://www.einstein-online.info/elementary/quantum/loops :

From the point of view of Einstein´s theory, it comes as no surprise that all attempts to treat gravity simply like one more quantum force (on par with electromagnetism and the nuclear forces) have failed. According to Einstein, gravity is not a force – it is a property of space-time itself. Loop quantum gravity is an attempt to develop a quantum theory of gravity based directly on Einstein´s geometrical formulation.

This approach is hard to explain in detail without resorting to the language of mathematics. Part of the problem is a still-unanswered question: Although this approach leads to a quantum formulation for gravity, researchers are still busy trying to work out how a universe like ours – which obeys the classical (i.e. non-quantum) general theory of relativity – can arise from such a quantum foundation.

One aspect of the loop models, though, is easy to grasp. Space, in general relativity, is a continuum. In every part of it, one can define regions of arbitrarily small volume, and every little region can be divided further into yet smaller regions, ad infinitum. In the loop models, the basic structure of space-time turns out to be discrete. In such discrete space-times, there are smallest values for volumes and areas that are not divisible any farther – just as one cannot build a structure smaller than the smallest block in a children's lego set. The fabric of space is called a spin network with lines and nodes, as pictured here:

Nodes can carry numerical values; depending on the number, they stand for volume building blocks of different size. The smallest possible volume is that of a region containing only a single node with the lowest possible value. As you add further nodes and/or make the values associated with existing nodes larger, the volume grows.

Thus, space acquires a grainy, discrete structure – and so does time.

[< retired >]

Researchers at Northeastern University and the University of California, Irvine say that scientists might soon have evidence for extra dimensions and other exotic predictions of string theory. Early results from a neutrino detector at the South Pole, called AMANDA, show that ghostlike particles from space could serve as probes to a world beyond our familiar three dimensions, the research team says...

The person who wrote this is a (most likely unconscious) verificationist. A verificationist believes that scientific theories are 'confirmed' (or made more probably true) by deducing predictions from them and then verifying these predictions via experimentation. A falsificationist, on the other hand, believes that scientific theories can never be confirmed (or considered more probably true) due to the results of experimentation, but can only be falsified.

The leading proponent of falsificationism during the 20th century was Karl Popper. Many philosophers of science had (and have) serious problems with falsificationism. In fact, it's safe to say that today verificationism reigns supreme among practicing scientists, to the extent that many of them are unconscious verificationists. I think that this is a shame. Verificationism (or falsificationism) should be a conscious choice, not an unquestioned default position.

For a recent attempt to rehabilitate Popper, check out this:

http://www.amazon.com/Poppers-Theory-Science-Continuum-Philosophy/dp/0826490263/ref=sr_1_45?s=books&ie=UTF8&qid=1295144308&sr=1-45

Now, back to our regularly scheduled program ... :)

[Kelly]

Loop Quantum Gravity

This is getting to be a hot topic for physicists, and you will likely hear about it from various media in the future.

Although String Theory is rather popular, some are uncomfortable with it, and even dislike it. Here is a jab:

There are valid criticisms of String Theory, as well as people who very much believe in it. The cartoon below is entitled How to answer stupid critics of string theory:

So, the debate is on. Some prefer a universe of 11 dimensions and many parallel universes, with gravity from one universe affecting others, and some prefer a universe in 4 dimensions made of spin foam.

(as far as I know, string theory can be used to calculate the entropy of black holes, despite Leslie's statement; also, it appears that the boys have a Spin Network diagram on their refrigerator—why would they have that if they oppose Loop Quantum Gravity?)

An interesting intro to the topic is Three Toads to Quantum Gravity by Lee Smolin. Two of these roads were String Theory and Loop Quantum Gravity. Smolin also has an intro to LQG:

Am invitation to Loop Quantum Gravity

[daveb]

Interesting stuff about loop quantum gravity. I've never seen much about it (other than the Big Bang Theory show bit that didn't register). It seems promising. I'll try to read that article later.

[Kelly]

In yesterday's news:

Higgs Boson Already Found?!?

Higgs Boson Already Found?

Posted on January 18, 2011 by Ira Flatow

The Higgs boson, which is being hunted at the Large Hadron Collider, has probably been found already, as early as 11 years ago, says Amir Aczel. Where? Probably, he says, in the particle smasher (LEP) that was dismantled to make way for the LHC, over a decade ago. And perhaps at Fermilab in Batavia, Illinois.

Really? When Aczel came on Science Friday to talk about his new book “Present At The Creation,”he dropped hints that the Higgs had already been discovered but had yet to be confirmed. “There is not enough statistical evidence yet,” he said. We need “99.99… percent confirmation.” Just like Sagan used to say: Extraordinary claims require extraordinary evidence.

But Aczel says he feels the evidence exists if scientists dig through the “noise” of the test results. One enticing piece of non-scientific evidence: Aczel says he’s already seen on the cafeteria wall of CERN, where they display pictures of particles found at the lab, a picture of the Higgs boson.

As for Fermilab, the Higgs “is probably there already.” Just sift through the data. The Cern folks are a bit concerned about being beaten to the punch. They aim to run the LHC straight through a scheduled maintenance stop next year, says Aczel.

And if they find it? So what. Lots of scientists don’t care, he says. “We want something more interesting,” like finding evidence for dark energy.

You just can’t satisfy some folks.

Hmm...

A Feynman diagram of one way the Higgs boson may be produced at the LHC. Here, two gluons decay into a top/anti-top pair, which then combine to make a neutral Higgs.

A Feynman diagram of another way the Higgs boson may be produced at the LHC. Here, two quarks each emit a W or Z boson, which combine to make a neutral Higgs.

A Powerpoint presentation on the search for the search for the Higgs Boson at the LHC is available here:

http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/Conferences/2003/aspen-03_dam.ppt

[Bobandirus]

Do excuse my poor physics knowledge, but doesn't the existence of the Higgs give more weight to The Standard Model, and more against string theory and other exotic stuff?

[michaeld]

Wow, lot of stuff to catch up on here. I'll try and post some replies later this evening. But one quick response.

Do excuse my poor physics knowledge, but doesn't the existence of the Higgs give more weight to The Standard Model, and more against string theory and other exotic stuff?

No. The Standard Model is expected to be a low energy limit of string theory. The Standard Model cannot itself be a complete theory as it does not contain gravity. (You can add classical gravity by hand but for a number of reasons this is not tenable in the high energy limit.)

The Higgs is an unusual case in that not finding the new particle (more precisely, showing it doesn't exist in the energy range it'd have to) would actually be much more interesting than finding it. Everyone expects it to exist. Indeed electroweak symmetry has to be broken somehow and the Higgs mechanism gives the likely answer. If it's shown not to exist then it'd mean there's very interesting new physics at reasonably low energies (compared to the Planck and String scales anyway).

[Bobandirus]

Fair enough :lol: My knowledge of that bits of physics is rubbish

[Kelly]

Can we do some real physics?

Y'know, macro scale stuff?

Here is something:

Red giant star Betelgeuse is mysteriously shrinking

The red supergiant star Betelgeuse, the bright reddish star in the constellation Orion, has steadily shrunk over the past 15 years, according to University of California, Berkeley, researchers.

Long-term monitoring by UC Berkeley's Infrared Spatial Interferometer (ISI) on the top of Mt. Wilson in Southern California shows that Betelgeuse (bet' el juz), which is so big that in our solar system it would reach to the orbit of Jupiter, has shrunk in diameter by more than 15 percent since 1993.

Since Betelgeuse's radius is about five astronomical units, or five times the radius of Earth's orbit, that means the star's radius has shrunk by a distance equal to the orbit of Venus.

"To see this change is very striking," said Charles Townes, a UC Berkeley professor emeritus of physics who won the 1964 Nobel Prize in Physics for inventing the laser and the maser, a microwave laser. "We will be watching it carefully over the next few years to see if it will keep contracting or will go back up in size."

Townes and his colleague, Edward Wishnow, a research physicist at UC Berkeley's Space Sciences Laboratory, will discuss their findings at a 12:40 p.m. PDT press conference on Tuesday, June 9, during the Pasadena meeting of the American Astronomical Society (AAS). The results were published June 1 in The Astrophysical Journal Letters.

Despite Betelgeuse's diminished size, Wishnow pointed out that its visible brightness, or magnitude, which is monitored regularly by members of the American Association of Variable Star Observers, has shown no significant dimming over the past 15 years.

The ISI has been focusing on Betelgeuse for more than 15 years in an attempt to learn more about these giant massive stars and to discern features on the star's surface, Wishnow said. He speculated that the measurements may be affected by giant convection cells on the star's surface that are like convection granules on the sun, but so large that they bulge out of the surface. Townes and former graduate student Ken Tatebe observed a bright spot on the surface of Betelgeuse in recent years, although at the moment, the star appears spherically symmetrical.

"But we do not know why the star is shrinking," Wishnow said. "Considering all that we know about galaxies and the distant universe, there are still lots of things we don't know about stars, including what happens as red giants near the ends of their lives."

Many people think that Betelgeuse will nova, or even supernova, likely within a million years. It would be an interesting sight.

Betelgeuse is the bright red star in the upper left of the consetellation Orion:

On the bottom right is the even brighter star Rigel.

Here is an infrared pic of Betelgeuse posted recently in Scientific American. Note the interesting bright spots:

[< retired >]

Many people think that Betelgeuse will nova, or even supernova, likely within a million years. It would be an interesting sight.

Not for the inhabitants of the planet Yerp, the fifth planet from the sun within the Betelgeusean solar system. Yerplings take a dim view of Earthlings casually discussing their ultimate demise. :)

[Kelly]

Wave function of Schrödinger's kitty:

The wave function collapses into a live or dead cat when you open the box and take a look.

However, I have the unpopular opinion that the cat is either alive or dead, not both (we just do not know which until we observe).

[cosmicbimbo]

Wave function of Schrödinger's kitty:

The wave function collapses into a live or dead cat when you open the box and take a look.

However, I have the unpopular opinion that the cat is either alive or dead, not both (we just do not know which until we observe).

My understanding was that in one universe the cat is alive and in another the cat is dead.

[Kelly]

My understanding was that in one universe the cat is alive and in another the cat is dead.

I hope that Dr. Michaeld shows up. He can probably discuss that in depth.

[cosmicbimbo]

My understanding was that in one universe the cat is alive and in another the cat is dead.

I hope that Dr. Michaeld shows up. He can probably discuss that in depth.

The question is, How far over my head will the explanation be"? :)

[Ged of Earthsea]

I agree with Joe's purity diagram - except it omits all those pesky logicians to the right of the mathematicians!

OMG! I can't believe someone mentioned logicians! I'm going to cry. I have found my Mecca. I think this moment defines disbelief for me.

[daveb]

Schroedinger's Cat - I thought it had something to do with the fact that how we observe something at that scale affects what we see, but it doesn't actually change the thing itself. The cat is an imperfect analogy, as any analogy must be when making such a leap. Maybe it's more like the cat could be either dead or alive (but not both at once), but we can't know until we open the box. Was it in one of these threads that someone talked about a theory where light is more discrete than we thought? That when you get down to it there is such a thing as the smallest possible amount of light, that can't be broken down further? Or I could just be rambling in over my head...

(it's about light as waves and as particles, right?)

Man, I'm feeling like a dunce. :redface: :lol:

[Sally]

*edited out really stupid post and left thread to those who know what they're talking about, or certainly more than I know*

[LonePiper]

Man, this thread really makes me regret taking an arts course intead of a science course :(

I like to think of myself as very well-informed for a layman, but the level most of you guys are on is making me feel very jealous.

Mind you, I'm not sure how well I would have done in physics as I detest maths (I'm quite good at it, I just don't enjoy it) but I could have gone into biology or even chemistry...

Still, I'm going to keep a close eye on this thread from now on. I read most of it already, but didn't understand everything. However I did understand more than I expected I would, thanks in part to "Fabric of the Cosmos" by the aforementioned Greene. (And various other popular science books and articles)

[michaeld]

However I did understand more than I expected I would, thanks in part to "Fabric of the Cosmos" by the aforementioned Greene. (And various other popular science books and articles)

Greene is very good. The Fabric of the Cosmos is actually his second book on String Theory and related topics - the first being The Elegant Universe. He now has a third book, being released this very week (edit: in fact it's today!!), called The Hidden Reality. This book is apparently about cosmology with particular emphasis on the possibility of parallel universes. Should be fun. My copy hasn't arrived yet though.

[Ged of Earthsea]

Loop Quantum Gravity (fer dummehz)

Kelly, I quite like the organisation of theories in the Bronshtein cube. It captures the different high-level ideas involved and charts a natural progression towards a unified theory.

[Kelly]

I like the way that the cube puts the theories.

Speaking of books for laymen, I am presently reading Three Roads to Quantum Gravity, by Lee Smolin. Like Greene's second book, it mentions Loop Quantum Gravity. The book is ten years old, and advances in LQG have been made since then, but it seems like a good intro.

[Herr Joseph von Löthing]

My friend made a physics joke in an email to a university admissions department today, as to why he had to reschedule an interview.

'I wish I could be in two places at once, but unfortunately I'm going to be observed in the physics exam.'

I laughed for about 5 minutes.

[Kelly]

Wave function of Schrödinger's kitty:

The wave function collapses into a live or dead cat when you open the box and take a look.

However, I have the unpopular opinion that the cat is either alive or dead, not both (we just do not know which until we observe).

My understanding was that in one universe the cat is alive and in another the cat is dead.

Oh, OK. That is the Many Worlds Interpretation, a.k.a., the Everett interpretation. Here, the universe splits in two, with the cat alive in one and dead in the other. These universes cannot interact with each other.

In the Schrödinger's kitty picture in the original post, we are using the Copenhagen weinterpretation, which makes the kitty a wave function of eigenvalues. The squares of the eigenvalues sum to 1:

In the example above, the kitty has a 50% chance of being alive, and the same for being dead (when observed).

The particle (or kitty, here) is often thought of as a sum of its eigenstates, so it is both alive and dead while it has this wave function.

When the particle (or kitty) is observed, then the wave function "collapses" and only one of its eigenstates will be true. Each possible eigenstate has a probability, so you can predict how many cats will be alive and how many are dead if you know the wave function (and we do—it is 50% each). If we observe a large amount of Schrödinger's kitties, we will end up with very close to half live ones and half dead ones.

The same as with a photon (or electron) when we allow it to go through one of two slits. If we observe the photons, we can count how many go through one slit or the other. But if we do not observe them, then they will go through both (and produce an interference pattern, since they will interfere with themselves).

Back to the Many Worlds Interpretation. Here, the kitty is not a superposition of a live and a dead cat, but it is either alive or dead in any given universe. Since it can be alive or dead, it is both, but in different universes. You, the observer, are in only one universe, so your kitty will be either alive or dead but not both. If the kitty is alive when you open the box and look, your doppelganger will observe a dead cat when he opens the box.

I don't really believe that, I tend to think that the cat is either alive or dead. True, we do not know which, but when there is an object (or particle) with possibilities that can be summed up in a wave function, I do not believe that universes are constantly splitting off. There are a lot of particles, and the creation of nearly an infinite number of universes, splitting off every time that there is a possibility to do so seems difficult. How many universes must there be by now?

Regarding the particles and kitties as superpositions of eigenstates, I have a problem. The entangled photon pair is a good example. With particles, such as two photons that are made at the same time, and traveling out away from each other with their polarization states at 90 degrees from each other.

Since their electric fields must be 90 degrees apart, then if, say, a year later, when the two photons are two light-years apart, one photon is "observed", or its polarity measured, then if the other photon's polarity is measured just afterwards, then it will (it must) show a polarity 90 degrees apart from the first photon.

Conventional thinking is that the photons' polarities are a wave function with possibilities of being measured in one direction or the other, and that it does not have a definite direction until it is measured (observed) and then its wave function "collapses" and it falls into one eigenstate. And since the other photon must have a polarity 90 degrees from it, the first photon signals the second photon and tells it to collapse its wave function and in what state it should become. And it does so instantly—far faster than the speed of light.

I disagree.

Whereas I do agree that the photon may be thought of as having a possibility of having its polarity in one direction of the other, and that it is unknown until it is measured, I do not think that it did not have a definite polarity until it was measured, but instead, it had one to begin with, when the photon pair was first created. So, a year after the pair was created, and the two photons are measured one right after the other (say, with the first photon's polarity at 90 degrees and the second at 0) and the results are beamed to our experimenters on earth), the experimenters may say, See, that proves superluminal communication, because the first photon had to tell the second photon to collapse its wave function, and it did so in less than a second from two light years away!

Not as far as I am concerned—I think that the reason why the second photon has its polarity at 0 degrees was not because it suddenly collapsed its wave function when the fist one did, but that its polarity already was at 0 degrees, and was ever since it was created.

I am sure that that is blasphemy, but there you have it.

*hides from the inquisitors*

[< retired >]

Back to the Many Worlds Interpretation. Here, the kitty is not a superposition of a live and a dead cat, but it is either alive or dead in any given universe. Since it can be alive or dead, it is both, but in different universes. You, the observer, are in only one universe, so your kitty will be either alive or dead but not both. If the kitty is alive when you open the box and look, your doppelganger will observe a dead cat when he opens the box.

I don't really believe that, I tend to think that the cat is either alive or dead. True, we do not know which, but when there is an object (or particle) with possibilities that can be summed up in a wave function, I do not believe that universes are constantly splitting off. There are a lot of particles, and the creation of nearly an infinite number of universes, splitting off every time that there is a possibility to do so seems difficult. How many universes must there be by now?

In his 1973 book Counterfactuals, philosopher David Lewis presented an argument for what I'll call 'possible world realism' - the belief that any possible world has the same ontological status (i.e., exists in exactly the same way) as the actual world. Needless to say, this position created a great deal of consternation among philosophers. IIRC, David Lewis made no reference whatsoever to quantum physics to support his argument.

I don't get involved in metaphysical arguments, but I do need to take a stance on the whole business of counterfactuals for my current project, hence my interest. The subject is surprisingly tricky, considering that most folks use counterfactuals constantly without even being aware what they are.

Lewis' book was reprinted in 2001, so you might be able to pick up a copy if you are curious what he had to say on this topic. I didn't find his possible worlds realism argument particularly compelling. :)

[LonePiper]

However I did understand more than I expected I would, thanks in part to "Fabric of the Cosmos" by the aforementioned Greene. (And various other popular science books and articles)

Greene is very good. The Fabric of the Cosmos is actually his second book on String Theory and related topics - the first being The Elegant Universe. He now has a third book, being released this very week (edit: in fact it's today!!), called The Hidden Reality. This book is apparently about cosmology with particular emphasis on the possibility of parallel universes. Should be fun. My copy hasn't arrived yet though.

Overall it was a good book, and I know about his others which I hope to read eventually. The only thing that bothered my about the book was his excessive use of Simpsons and X-Files related analogies. They just felt tacky and a little patronising.