Wednesday, April 29, 2015

IceCube Neutrinos Are Truly Cosmic

Latest data analysis from IceCube concludes that the neutrinos that had been reported are consistent with them having a cosmic origin.

Two groups have now analyzed a larger data set (covering years 2010 to 2013). The first work, conducted by the IceCube collaboration, identifies a total of 137 high-energy neutrinos (above 35 tera-electron-volts). The team shows that the number of tracks to showers is incompatible with exotic flavor ratios, such as 1:0:0 and 0:1:0. A similar analysis was performed by theorists at Italy’s Gran Sasso Science Institute in L’Aquila and the Gran Sasso Laboratories in Assergi. They focus on a higher energy range (above 60 tera-electron-volts) and find the ratio of tracks to showers is consistent with several astrophysical (nonexotic) models. Future data and analysis, which may include a method for tagging tau neutrinos, could eventually distinguish between these different source models.

I want to always try to impress upon people reading this, especially non-scientists, on how this is an example of "Physics doesn't just say what "What comes up, must come down". It must also say when and where it comes down!" In other words, there must be a strong QUANTITATIVE aspect of physics.

In this example, just detecting neutrinos is not sufficient (i.e. you found out that what goes up, must come down). The energy of the neutrinos, the interaction channels, etc...etc. are strict, mathematical descriptions that make numerical predictions (i.e. when and where it comes down). Only when the data are compared to these models can one distinguishes the type and nature of these neutrinos. Without the quantitative aspect of the physics, a neutrino will look like any other neutrinos.

Zz.

Tuesday, April 28, 2015

History of Physics Education in the US

I've only managed to read about 1/3 of the paper so far, but I thought I should highlight it on here for discussion for those so inclined.

There is a 12-page paper on the history of physics education in the US published in this month's issue of AJP[1]. Even though it is a "brief" overview of the history, it has to be one of the most comprehensive survey of physics education in the US that I've ever come across. It begins all the way back from 1860s to the present day, and looked at what has changed and what has remained the same.

I think that it is interesting to see some of the same efforts and arguments being made way back then, and to see how some things just are implemented or aren't effective. There's a lot of history to be learned from this paper because people tend to have short memory and do not remember what works and what doesn't.

Zz.

[1] D.E. Meltzer and V.K. Otero, Am. J. Phys. v.83, p.447 (2015).

Thursday, April 23, 2015

How Big Is The Sun?

Hey, you get to use some of your high-school geometry and trig to make sense of this video!



Zz.

Accelerator Development For National Security

So let me point out this news article first before I go off on my rant. This article describes an important application of particle accelerators that has an important application in national security via the generation of high-energy photons. These photons can be used in a number of different ways for national security purposes.

The compact photon source, which is being developed by Berkeley Lab, Lawrence Livermore National Laboratory, and Idaho National Laboratory, is tunable, allowing users to produce MeV photons within very specific narrow ranges of energy, an improvement that will allow the fabrication of highly sensitive yet safe detection instruments to reach where ordinary passive handheld sensors cannot, and to identify nuclear material such as uranium-235 hidden behind thick shielding. "The ability to choose the photon energy is what would allow increased sensitivity and safety. Only the photons that produce the best signal and least noise would be delivered," explains project lead Cameron Geddes, a staff scientist at the Berkeley Lab Laser Accelerator (BELLA) Center.
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To make a tunable photon source that is also compact, Geddes and his team will use one of BELLA's laser plasma accelerators (LPAs) instead of a conventional accelerator to produce a high-intensity electron beam. By operating in a plasma, or ionized gas, LPAs can accelerate electrons 10,000 times "harder" or faster than a conventional accelerator. "That means we can achieve the energy that would take tens of meters in a conventional accelerator within a centimeter using our LPA technology," Geddes says.

I've mentioned about this type of advanced accelerator scheme a few times on here, so you can do a search to find out more.

Now, to my rant. I hate the title, first of all. It perpetuates the popular misunderstanding that accelerators means "high energy physics". Notice that the production of light source in this case has no connection to high energy physics field of study, and it isn't for such a purpose. The article did mention that this scheme is also being developed as a possible means to generate future high-energy electrons for particle colliders. That's fine, but this scheme is independent of such a purpose, and as can be seen, can be used as a light source for many different uses outside of high energy physics.

Unfortunately, the confusion is also perpetuated by the way funding for accelerator science is done within the DOE. Even though more accelerators in the US is used as light sources (synchrotron and FEL facilities) than they are for particle colliders, all the funding for accelerator science is still being handled by DOE's Office of Science High Energy Physics Division. DOE's Basic Energy Sciences, which funds synchrotron light sources and SLAC's LCLS, somehow would not consider funding advancement in accelerator science, even though they greatly benefit from this field. NSF, on the other hand, has started to separate out Accelerator Science funding from High Energy Physics funding, even though the separation so far hasn't been clean.

What this means is that, with the funding in HEP in the US taking a dive the past several years, funding in Accelerator Science suffered the same collateral damage, even though Accelerator Science is actually independent of HEP and has vital needs in many areas of physics.

Articles such as this should make it clear that this is not a high energy physics application, and not fall into the trap of associating accelerator science with HEP.

Zz.
The compact photon source, which is being developed by Berkeley Lab, Lawrence Livermore National Laboratory, and Idaho National Laboratory, is tunable, allowing users to produce MeV photons within very specific narrow ranges of energy, an improvement that will allow the fabrication of highly sensitive yet safe detection instruments to reach where ordinary passive handheld sensors cannot, and to identify such as uranium-235 hidden behind thick shielding. "The ability to choose the photon energy is what would allow increased sensitivity and safety. Only the photons that produce the best signal and least noise would be delivered," explains project lead Cameron Geddes, a staff scientist at the Berkeley Lab Laser Accelerator (BELLA) Center.

Read more at: http://phys.org/news/2015-04-national-high-energy-physics.html#jCp
The compact photon source, which is being developed by Berkeley Lab, Lawrence Livermore National Laboratory, and Idaho National Laboratory, is tunable, allowing users to produce MeV photons within very specific narrow ranges of energy, an improvement that will allow the fabrication of highly sensitive yet safe detection instruments to reach where ordinary passive handheld sensors cannot, and to identify such as uranium-235 hidden behind thick shielding. "The ability to choose the photon energy is what would allow increased sensitivity and safety. Only the photons that produce the best signal and least noise would be delivered," explains project lead Cameron Geddes, a staff scientist at the Berkeley Lab Laser Accelerator (BELLA) Center.

Read more at: http://phys.org/news/2015-04-national-high-energy-physics.html#jCp

Wednesday, April 22, 2015

Quantum Entanglement For Dummies

Over the years, I've given many references and resources on quantum entanglement on this blog (check here for one of the more comprehensive references). Now, obviously, many of these sources are highly sophisticated and not really meant for the general public. It is also true that I continue to get and to see question on quantum entanglement from the public. Worse still, the Deepak Chopras of the world, who clearly do not understand the physics involved, are bastardizing this phenomenon in ridiculous fashion. But the final straw that compelled me to write up this thing is the episode of "Marvel Agent of Shield" from last night where the top brass of HYDRA was trying to explain to Bakshi what "quantum entanglement" is and how Gordon was using it to teleport from one location to another. ABSURD!

So while this is all brought about by a TV series, it is more of a reflection on how so many people are really missing the understanding of this phenomenon. So I intend to explain this is very simple language and using highly-simplified picture to explain what quantum entanglement is. Hopefully, it will diminish some of the false ideas and myth of what it is.

Before I dive into the quantum aspect of it, I want to start with something that is well-known, and something we teach even high school students in basic physics. It is the conservation of momentum. In Figure 1, I am showing a straight-foward example of conservation of linear momentum case, a common problem that we give to intro physics students.


In (a), you have an object with no initial linear momentum. In (b), it spontaneously splits into two different masses, m1 and m2, and go off in opposite directions. In (c), m1 reaches Bob and m2 reaches Alice. Bob measures the momentum of m1 to be p1.. Now, this is crucial. IMMEDIATELY, without even asking Alice, Bob knows unambiguously the momentum of m2 to be p2 simply via the conservation of linear momentum. He knows this instantaneously, meaning the momentum of m2 is unambiguously determined, no matter how far m2 is from Bob. When Alice finally measures the momentum of m2, she will find that it is, indeed, equal to p2.

Yet, in all the years that we learn classical physics, never once do we ever consider that m1 and m2 are "entangled". No mystical and metaphysical essays were ever written about how these two are somehow connected and can "talk" to each other at speeds faster than light.

Now, let's go to the quantum case. Similar scenario, outlined in Figure 2.


Here, we are starting to see something slightly different. We start with an object with no net spin in (a). Then it spontaneously splits into two particles. This is where it will be different than the classical case in Figure 1. Each of the daughter particles has a superposition of two possible spin states: up and down. This is what we call the SUPERPOSITION phenomenon. It was what prompted the infamous Schrodinger Cat thought experiment where the cat is both alive and dead. This is crucial to understand because it means that the state of each of the daughter particle is NOT DETERMINED. Standard QM interpretation says that the particle has no definite spin direction, and that until it is measured, both spin states are there!

Now, when one daughter particle reaches Bob, he then measures it spin. ONLY THEN will the particle be in a particular spin state (i.e. the commonly-described as wavefunction collapsing into a particular value). In my illustration, Bob see that it is in a spin-down state. Immediately, the spin state of other particle at Alice is in the spin-up state to preserve the conservation of spin angular momentum. When Bob measures the pin of his particle, he immediately knows the spin of the particle at Alice because he knows what it should be to conserve spin. This is similar to the classical case!

This superposition of state is what makes this different than the above classical example. In the classical case, even before Bob and Alice measure the momentum of their particles, there is no question that the particles have definite momenta all through its trajectory. Classical physics says that the momentum of each particle are already determined, we just need to measure them.

But in quantum physics, this isn't true. The superposition principle clearly has shown that in the creation of each of those two particles, the spin state are not determined, and that both possible states are present simultaneously. The spin state is only determined once a measurement is made on ONE of the particles. When that occurs, then the spin state of the other particle is also unambiguously determined.

This is why people have been asking how the other particle at Alice somehow knew the proper spin state to be in, because presumably, before any measurement is made, they both can randomly select either spin state to be in. Was there any signal sent from Bob's particle to Alice's to tell it what spin state to be in? We have found no such signal, and if there is, it has been shown that it will have to travel significantly faster than c. No matter how far apart the two daughter particles are, they somehow will know just what state to be in once one of them is measured.

This, boys and girls, is what we called quantum entanglement. The property of the quantum particles that we call "spin" is entangled between these two particles. Once the value of the spin of one particle is determined, it automatically forces the other particles to be in a corresponding state to preserve the conservation law.

But note that what is entangled is the property of the particle. It is the information about the property (spin) that is undergoing the so-called quantum teleportation. The particle itself did not get "teleported" the way they teleport things in Star Trek movies/TV series. It is the property, the information about the object, that is entangled, not the entire object itself. So in this example, the object doesn't jump around all over the place.

The physics and mathematics that describe quantum entanglement are more involved than this cartoon description, of course. There are mathematical rules resulting in physical constraints to the states and properties that are entangled. So you just can't pick up anything and say that you want to entangle it with something else. It just doesn't work that way, especially if you want to clearly observe the effects of the entanglement.

The important lesson to take away from this is that you can't learn physics in bits and pieces. If you simply focus on the "entanglement" aspect and are oblivious to understanding the existence of quantum superposition, then you will never understand why this is very different and mysterious than the classical case. In physics, it is not uncommon that you have to also understand a series of things leading up to it. This is why it is truly a knowledge and not just merely a series of disconnected information.

Zz.

Monday, April 20, 2015

Cyclotron Radiation From One Electron

It is a freakingly cool experiment!

We now can see the cyclotron radiation from a single electron, folks!

The researchers plotted the detected radiation power as a function of time and frequency (Fig. 2). The bright, upward-angled streaks of radiation indicate the radiation emitted by a single electron. It is well known theoretically that a circling electron continuously emits radiation. As a result, it gradually loses energy and orbits at a rate that increases linearly in time. The detected radiation streaks have the same predicted linear dependence, which is what allowed the researchers to associate them with a single electron. 

Of course, we have seen such effects for many electrons in synchrotron rings all over the world, but to not only see it for one electron, but to also see how it loses energy as it orbits around is rather neat. It reinforces the fact that we can't really imagine electrons "orbiting" around a nucleus in an atom in the classical way, because if they do, we would detect such cyclotron radiation and that they will eventually crash into the nucleus.

But I also find it interesting that this has more to do with the effort in trying to determine the mass of a neutrino independent of the neutrino mass oscillation via measuring the electrons mass to high accuracy in beta decay.

Zz.

Saturday, April 18, 2015

Complex Dark Matter

Don Lincoln has another video on Dark Matter, for those of you who can't enough of these things.



Zz.

Thursday, April 16, 2015

Tevatron Data Reveals No Exotic, Non-Standard Model Higgs

She may be long gone, but the old gal still has something to say.

A new paper that combined the data from CDF and D0, the two old Tevatron detectors at Fermilab, has revealed that the Higgs that has been found is indeed consistent with the Standard Model Higgs. It strengthens the much-heralded discovery made at CERN a while back.

...... the two Tevatron-based experiments, CDF and D0, uncovered evidence in 2012 of a Higgs boson decaying into fermions, specifically, a pair of bottom quarks. The two collaborations have again combined their data to check for exoticness in this fermion decay channel. The Tevatron data show no signal consistent with a Higgs boson having spin zero and odd parity (a so-called pseudoscalar) or spin 2 and even parity (gravitonlike). The results are important for building the case that the Higgs boson seen in particle colliders is indeed the standard model Higgs.

Zz.

More Quantum Physics In Your Daily Lives

I pointed to an article a while back about the stuff we use everyday that came into being because of our understanding of quantum mechanics (basically, all of our modern electronics). Now, Chad Orzel has done the same thing in his article on Forbes, telling you how you actually start your mornings by relying on the validity of QM.

The tiny scale of all the best demonstrations of quantum physics can lead people to think that this is all basically meaningless, arcane technical stuff that only nerds in white lab coats need to worry about. This is deeply wrong, partly because I don’t know any physicists who wear white lab coats, but more importantly because quantum phenomena are at the heart of many basic technologies that we use every day.

In fact, I can’t start my morning without quantum mechanics, in the form of my bedside alarm clock.

You may read the rest of his arguments in the article.

I will also add something that I've mentioned before. The presence of quantum effects may be more prominent than what most are aware of, if we go by the evidence for the existence of superconductivity. As stated by Carver Mead, it is the clearest demonstration of QM effects at the macro scale. Yet, a lot of people simply do not recognize it for what it is.

Zz.

Wednesday, April 15, 2015

Use "i,j,k" notation instead of "arrow" representation for vectors in Intro Physics?

That is what the authors of this study have found to be more effective in analyzing students understanding and ability to comprehend vector problems. (The paper is available for free.)

First, we replicated a number of previous findings of student difficulties in the arrow format and discovered several additional difficulties, including the finding that different relative arrow orientations can prompt different solution paths and different kinds of mistakes, which suggests that students need to practice with a variety of relative orientations. Most importantly, we found that average performance in the ijk format was typically excellent and often much better than performance in the arrow format in either the generic or physics contexts.

My question is, is this the result of an inherent conceptional problem in the arrow representation, or simply a matter of correcting some of the ways we teach vectors to students?

Zz.

Thursday, April 09, 2015

How Do Airplanes Fly?

I get asked this often, strangely enough. So it is nice to have a quick illustration via a video on how it works.



Zz.

Where HEP Technology Becomes Commercial

This is a nice article to introduce you to all the benefits that the rest of world gets from the innovations that came about due to the experimental needs in high energy physics, nuclear physics, astrophysics, etc. The effort of HEPTech is clearly to make the technology transfer a conscious and systematic one, rather than just ad hoc or via accident.

Zz.

Wednesday, April 01, 2015

CERN Confirms The Existence of The Force

I can't let April 1st go without at least one goofy post, can I? So here it is!

Zz.

When Physics Demo Goes Wrong

Ouch!!!

Just found this news article on a physics demo for an AP physics class that didn't go as planned.

It apparently shows a physics teacher teaching a class a lesson by taking aim at a concrete block.

But he doesn’t quite hit the block correctly and ends up hitting a fellow teacher in a very sensitive area.


Now I'm all for doing demos in class, since not only can they be educational and fun, it also keeps the students from falling asleep. But I don't know if this is a bit on the more "daring" side. There's certainly plenty of chances for things to go wrong with demo such as this.

If anyone has any follow-up news on this, please let me know. The YouTube video implied that the teacher doing the demo lost his job, and there's confusion on the person holding up the blocks and got hit was another student or another teacher.

Zz.