Questions and Answers from Virtual Ask-a-Scientist of January 29, 2004
More information about the program
Moderator
Welcome to Virtual Ask-a-Scientist! Chris and Ken are ready for your questions!
Ken Bloom
I'd like to point out that the temperature at Fermilab tonight is -1 degree Farenheit. At these temperatures, our brains go superconducting, so Chris and I will be able to answer your very difficult questions tonight!
Moderator
Ken and Chris are part of Fermilab's CDF experiment. Learn more about CDF here: http://www-cdf.fnal.gov/
PhysicsPhans
Has the mass of the Higg's Boson been determined yet?
Chris Hays
Not yet, we haven't even seen it yet, we hope to see within the next five years. There is some evidence its weight is between 115 and 150 times the weight of a hydrogen atom, but there are a number of assumptions that go into that estimate.
aheidar
What is a black hole?
Chris Hays
A black hole is an object with such a large gravitational force that nothing can escape, not even light.
Mary
What is a black hole and how does it relate to physics
Chris Hays
Black holes have so much mass that not even light can escape their graviational pull. Evidence for black holes has been observed at the center of a number of galaxies, and we believe there is even a black hole at the center of the Milky Way!
alis
how can you explain the aurora borealis using physics?
Ken Bloom
There is a lot going on with the aurora borealis! It starts with the "solar wind," which is a stream of charged particles that come out from the sun. It's not very well understood. But when these come into the earth's magnetic field, under certain conditions they are accelerated, and knock into gas atoms in the atmosphere. This gives energy to the atmosphere atoms and excites them, and then they emit that energy in the form of light, much like a neon sign.
topJunkies
Why does Fermilab have buffalo?
Moderator
Fermilab is famous for its buffalo! We have a heard of about 30 right now. Their numbers will be up to about 60 in the spring when they have their babies. Fermilab's reason for having buffalo actually goes back to our founding director, Robert Wilson. He wanted the lab to more than just a place for science. He was an outdoors man himself from Wyoming, and had an appreciation for nature. We have the buffalo to really remind us of our prairie heritage.
Erol
If extra dimensions do exist, what purpose can they serve?
Ken Bloom
Well, you can't use them for extra closet space. The idea is that gravitons, the particles that carry the force of gravity, can travel in those extra dimensions, unlike the normal everyday particles that you and I are made of. Because the gravitons can spread out like that, the force of gravity becomes weak compared to other forces, like electromagnetic forces. So if the extra dimensions exist, we need them to keep gravity weak.
Moderator
Thanks for all of your great questions! Please be patient as Chris and Ken are working away!
Mary
how does a lightning work
Ken Bloom
Ever walk on the carpet on a dry, cold day, and then touch a piece of metal, and you get a little shock? That's a miniature form of lightning. What happens is that you are picking up some extra electric charge by walking on the carpet, and that charge jumps to the metal when you touch it. This makes a little spark. Lightning happens when rain clouds accumulate a lot of charge, and that charge jumps to the earth -- making a very big spark!
topJunkies
We are wondering how we can see live particle collisions... I heard we can actually see them!
Chris Hays
There are many kinds of particle collisions, particles collide at low energies all around us. The kind of interesting, high-energy collisions, we produce at Fermilab, annihilate protons and anti-protons into rarer forms of matter, such as top quarks. We don't observe these collisions like we observe the rest of the world (with our eyes), rather we use fancy particle detectors to observe the results of the collision. We can use these detectors to 'see' things like muons, electrons, photons, and quarks, and we can reconstruct exotic particles like the top quark.
PhysicsPhans
Are the buffalo ever slaughtered? Who gets to eat the resulting food?
Moderator
Some of the buffalo are auctioned off every year in fall. Some go to breeders and others do get slaughtered.
Don S.
Hello all, thanks for your time tonight. It is bitter cold and a good night to be inside.
Moderator
Hi Don - It's bitter cold here too. Chris and Ken are ready for your questions. Fire away!
Erol
The graviton has been "indirectly observed", how is that?
Ken Bloom
I'm not sure that the graviton has been indirectly observed, beyond the fact that we know that gravity is a real force, and there must be a particle that carries that force. If we do discover those extra dimensions, then that would probably be indirect evidence for gravitons.
aheidar
what creates this extreme gravitational force?
Chris Hays
An extremely large amount of mass in a small space produces the gravitational force necessary to produce a black hole.
Mary
How much force is used to create a lightning?
Ken Bloom
A typical bold of lightning has the power of one million million watts. So that's the power of ten thousand million 100 W lightbulbs like the ones in your home!
Cid_H
How close have physicists gotten to finding a unified filed theory.
Ken Bloom
Depends on whom you ask! Theoretical physicists, who construct the mathematical models used to predict physics phenomena, have come up with very many grand unified theories. But the experimental physicists, who test these models, have yet to verify any of those theories. One interesting prediction of many GUTs is the decay of the proton. People have been looking for years, but have yet to find any evidence for proton decay.
theta
I'm creating an animation of an atom. Should electrons be represented as strings, balls, or clouds?
Chris Hays
Quantum mechanics describes electrons as clouds surrounding the nucleus. The clouds represent the range of positions one would observe from a large number of measurements of the electrons within the atom.
topJunkies
So, what exactly are these extra-dimensions? Can we travel through them?
Ken Bloom
We can't, to our knowledge...otherwise we probably would have done so already! We believe that only certain kinds of particles can travel in the extra dimensions, and we're not made of them. Sorry, you are stuck here.
Annie
What project are you currently working on at Fermilab??
Ken Bloom
I work on CDF, which is an experiment that studies what happens in proton-antiproton collisions at the Fermilab Tevatron. My particular interest is in the physics of the top quark, the most recently discovered and by far the heaviest of the six quarks.
Moderator
Fermilab produced its first high-energy particle beam on March 1, 1972. Since then hundreds of experiments have used Fermilab's accelerators to study matter at ever smaller scales. Here an overview of the top ten achievements so far. http://www.fnal.gov/pub/inquiring/physics/discoveries/index.html
Erol
Does anti-matter travel back in time?
Chris Hays
No, anti-matter simply describes particles that have exactly the opposite charge as particles.
Erol
Time stops in a black hole (accroding to theories), possibly how and why?
Ken Bloom
Inside a black hole, the curvature of space-time is infinite, and under those conditions "time" is not a very good concept. So that's effectively like it being stopped.
Moderator
Wow! We are getting a terrific response from all of you! Thanks for sending all of your great questions. Chris and Ken are answering them one by one. Thanks for your patience!
Don S.
I'd like to revisit a question asked last month, electron + positron annihilation, what happens to the gravitational field? At first it seemed plausible that a graviton should be emitted in addition to the 2-511kev photons. However, after reading a bit more I've seen references to GR describing warped space-time due to energy alone, no mass. I am not a student of GR, can you help me out here, do photons warp space-time, i.e., manifest gravity? Is this how to account for the gravitational field of the two particles after annihilation?
Chris Hays
Yes, that's exactly it. Gravity is produced by energy, and since massive objects have such a large amount of energy (remember Einstein), the largest gravitational effects come from massive objects. But energy, such as the photons from light, also produce gravity.
Charles
Since there is so much space between atoms and the particles that make them up, it's been a common theory idea that one could just 'get stuck' in an object (i.e. walking down the road, atoms of my shoe and the road interlock).... what keeps this from happening?
Ken Bloom
And for that matter, if you are made of atoms, and the chair is made of atoms, why don't your atoms slip right through the chair's atoms? The forces that bind your shoe together are stronger than any forces that might bond your shoe to the road. Why particular materials stay together while others stick to other things or get enmeshed in them is a matter of the chemistry of that material.
topJunkies
Thank you for telling me about how we can't "see" the collisions, but used detectors to see electrons, muons, and those guys. But how do you separate pions from kaons?
Ken Bloom
That can be hard! There are two different ways, and both depend on the fact that the pion and kaon have different masses. Because of that, they will lose energy in material at different rates, so we can try to measure the energy loss of the particles. Also, a pion and kaon of the same momentum will travel at different velocities, so if we can measure the velocity of the particle, and its momentum, we can determine the mass, and thus whether it's a pion or a kaon.
Erol
Is it possible that there are "smaller" particles than the already known elementary particles? I mean strings (theoretically) are many times smaller than the known elementary particles, therefore couldn't smaller particles compose these known elementary particles?
Chris Hays
Yes, this is exactly the type of thing we look for at Fermilab -- right now there is a graduate student in my group who is looking for evidence that electrons are actually composed of smaller particles. So far, there has been no evidence for "compositeness," as the theory is called, but we are still looking. We are still very far from the string scale, however, so there is lots of room for compositeness.
Erol
Under what circumstances does a mass collapse in order to form a black hole?
Ken Bloom
I'm not sure that the formation of black holes is very well understood. But if you have sufficient mass at a sufficient density, you will get a black hole. In particular, there is a special value of a mass for stars, and if a star is more massive than that value, something has to happen to it. One option is that it becomes a black hole.
Charles
What kinds of practical applications does research with Particle Physics have?
Ken Bloom
It's hard to point to any immediate practical applications. But to do this kind of physics, we have to develop all sorts of technology, and some of that has had some very important applications. Did you know that the World Wide Web started as a system that particle physicists developed to share information and documents between computers? We also do a lot of work in electronics and computing that can have applications outside of our research. Of course, in the end, you never know what you are going to get when you do basic research in fundamental physics. There may be applications that emerge decades from now which will stem from the research we are doing today!
Erol
What is required to become a physicist a FermiLab?(Years of school, degrees) And how difficult is ir to acquire a position?
Chris Hays
We have people with a range of degrees working at Fermilab studying the collisions. The professors organize the research for their university, they have Ph.D's, and professorships are very competitive. The physicists most directly involved with the experiments are post-doctoral researches, who spend their entire time working on the experiment and are not distracted by classes. Both Ken and I are postdoctoral researchers. There are also graduate students, who are using the data to write a doctoral thesis. Finally, we have undergraduates, who typically spend a summer to help build some component of the detector or to help analyze the data.
KQ
(This user has entered Fermilab Virtual Ask-a-Scientist) (IP = 64.252.197.232)
Guest
What research is being done with lightning right now
Ken Bloom
I'm not sure if this is the answer you are looking for, but let's try! Of course, lightning has important effects on the earth -- the associated thunderstorms affect our climate and all that energy being discharged in a lightning strike can affect the atmosphere. So there is a lot of work being done to track lightning storms and follow up on their potential effects.
barnabus
There's a lot of hubub about a new linear collider at Fermilab. Why is that needed?
Chris Hays
Historically, we have achieved the greatest understanding through a complementary approach of producing the highest energy collisions to search for new heavy particles (as is done here at Fermilab) and of producing very clean collisions (as has been done at CERN in Switzerland) to measure the known particles very precisely. The linear collider would provide a very clean environment with which to measure the Higgs particle. The Higgs hasn't been discovered yet, though, and that will be the role of the Large Hadron Collider at CERN. Once they find it, we'll know how to tune our linear collider to measure it very precisely.
Erol
I've heard that the Riemann Hypothesis has something to do with the nucles of an atom, do you know anything about this by chance?
Ken Bloom
Chris and I don't think we know anything about this. Can you be more specific?
PhysicsPhans
What do you think (as a scientist) about our president's desire to send astronauts to Mars?
Ken Bloom
As a scientist, I think that it will be very interesting to study Mars. Is the earth a unique planet, or could it be that there are lots of others like it? The rovers that are operating on Mars even as I write are working on this problem, and I think that unmanned missions will be our best source of science about Mars for many years to come. There are going to be many challenges in sending humans to Mars, and in the time it takes to solve them, we should be able to learn a lot about the red planet with robotic missions.
Brianne
what is a charged hadron? I have heard about this, but never understood what is was or where it is located
Ken Bloom
A hadron is a particle that is made of quarks. Protons and neutrons are hadrons, but electrons are not. A charged hadron is a hadron that carries a net electric charge. So the proton is a charged hadron, and the neutron is not. There are many other kinds of charged hadrons (and neutral ones, for that matter) that we see in particle-physics experiments, but not in everyday life.
theta
I know the cloud theory, but how would you visualize it? Is it a steam cloud around a few central nucleons--how would one actually animate an electron?
Chris Hays
The cloud is at some fixed radius, and there is a certain probability of finding the electron at a given point on the cloud. If this is a computer animation, you could produce an opaque cloud surrounding the nucleus at a given radius. The most easy model to visualize is of the electron orbiting the nucleus, which doesn't demonstrate the probabilistic aspects of the atom, but is otherwise a reasonable model.
PhysicsPhans
Referring back to Erol's anti-matter question: Does that mean that an electron is the "anti-matter" of a proton?
Ken Bloom
No. A particle and its anti particle always have the same mass, and the electron is about 2000 times less massive than the proton. The antimatter partner of the electon is the positron, and the antimatter partner of the proton is the antiproton.
Moderator
We are getting some queries about the Riemann Hypothesis. Here is a webpage that sums gives some more information: http://www.math.ubc.ca/~pugh/RiemannZeta/RiemannZetaLong.html
Kristin
What causes the intense gravitational force within blackholes?
Ken Bloom
It's the amazing concentration of mass inside a black hole, sufficient to cause a tremendous curvature of space-time. I hope that's a good enough answer for you -- try again if it isn't!
Erol
Is the force of gravitiy infinite?
Ken Bloom
It is infinite in extent -- the gravitational field of an object goes on forever, but the strength of that field (and therefore of the force) falls off pretty rapidly with the distance from the object. The only way to get a truly infinite force, however, would be to have a truly infinite mass, and that doesn't happen.
Erol
Will the LHC produce results that the Tevatron can't?
Ken Bloom
We hope so! The LHC will produce collisions that are seven times more energetic than those we have at the Tevatron. Einstein said that E = mc^2, which means that energy can be converted to mass. This means that we should be able to produce more massive particles at the LHC than we can at the Tevatron. Those massive particles would be new discoveries for us.
Moderator
Sign up for the Interactions.org high-energy physics news wire: http://www.interactions.org/
Guest
what is a charged hadron? and where is this located at in the atom
Ken Bloom
See above -- the proton is a charged hadron, and protons sit in the atomic nucleus.
KQ
What does LHC stand for?
Moderator
It stands the Large Hadron Collider, which is being built in Switzerland.
KQ
At CERN?
Moderator
That's right.
Guest
I have heard that you can use light to learn about the components of proteins...how does this work
Ken Bloom
You can determine the shape of objects by shining light on them, and seeing how the light is reflected (scattered, really) off the object. Different molecules have different scattering patterns, so intense light sources can be used to understand the shape of protein molecules, and therefore the amino acids that comprise them.
Don S.
Thank you Chris, that's pretty darn interesting. Are higher energy photons deflected to a greater degree by gravitational fields than lower energy, like a type of birefringence?
Chris Hays
Our most fundamental understanding of gravity is that it is the curvature of space-time (Einstein again). Anything travelling in a gravitational field follows a curved trajectory along a space-time path. In this model, the energy of the particle in the gravitational field does not matter, just the field itself. It is the same reason that all objects fall with the same acceleration when dropped near the surface of the Earth. The higher energy photon will *produce* a larger gravitational field than a lower energy photon, but it will be deflected the same amount when it encounters a gravitational field.
Erol
Are you aware of the Superconducting Super Collider (SSC)? What's outlook for it if there is any?
Moderator
The SSC was cancelled about ten years ago. I would say that the outlook is pretty bleak.
Kristin
At what rate is the universe expanding?
Ken Bloom
It's around 80 km/s/Mpc -- that is, stars that are a megaparsec away from us appear to be receding from us at the rate of 80 kilometers per second.
KQ
What was the SSC looking for?
Moderator
They were looking for the same stuff that we are: fate of the universe, dark energy, dark matter, higgs, amongst other stuff.
Ken Bloom
Not sure -- maybe you mean the photoelectric effect? This can be used to measure Planck's constant. Try us again?
Guest
how large is a neutrino?
Chris Hays
As far as we can tell, a neutrino is a fundamental particle and we have not been able to measure its size. The best we can say is that it is very, very small. The nucleus of the atom is a million times smaller than the atom. We know that the neutrino is at least a million times smaller than the nucleus. At Fermilab, we are able to extend this limit, and at the Large Hadron Collider in Switzerland, they will be able to go to distances ten times smaller.
Erol
If Earth or Earth's gravity collapses, will its gravitational pull be the same?
Ken Bloom
If the earth were to collapse, but the mass were to remain constant, then the gravitational pull would be the same, sure. If the earth were to lose mass in this collapse, then no, it would not.
KQ
Will the LHC look for the Higgs boson as well?
Moderator
Yes it will. The Higgs is still a very big quest for physicists. If Fermilab does not find it, there is a very good chance that the LHC will because it will be close to 4 times the size of the Tevatron.
topJunkies
So, what will have to be done to make it so that humans can walk on Mars?
Ken Bloom
The biggest problem is that humans have to get to Mars before they can walk on it. It's going to be a long trip, so they'll need lots of supplies, and it's going to take a very large rocket to launch the astronauts and everything they need. (They might want a building to live in on Mars, too.) Also, there is a lot of radiation in space, and the astronauts will have to be protected from it.
Guest
are you doing any work in the area of the imaging of radioactive materials?
Chris Hays
No, though I did spend one of my college summers at a cyclotron that produced Technicium, which is a radioactive material used to identify tumors.
Erol
When the LHC is built, won't the Tevatron be obsolete?
Moderator
Not necessarily. Fermilab is working on a lot of exciting physics beside just looking for the higgs. Everyone here is very excited about dark energy and dark matter right now. Fermilab could make contributions to discovering things about supersymmetry and extra dimensions that could lead to answers about how the universe was created and where it was going. It's pretty exciting stuff. And then there is always the possibility of discovering something that we are not expecting - that's the best kind of discovery.
Guest
do you do any work in the area of radioactive matter?
Ken Bloom
No, I don't. Occasionally it's useful for me to test a particle detector with a radioactive source, if we don't have a particle beam at our disposal. But that's for the purpose of studying the detector, not the radioactive material.
mazz
did you glow?
Ken Bloom
No, unless I was particularly happy at the time.
KQ
I was reading an article a few days ago and came across the term "Chiral Global Symmetry" {referring to neutrinos}. I was wondering if you could please tell me what this means.
Chris Hays
The Standard Model has an inherent symmetry between "left-handed" and "right-handed" particles. This symmetry can be broken when a particle has mass, but since the neutrinos were believed until recently not to have mass, this symmetry was expected to hold for neutrinos. All particles have a property called "spin." If you point your thumb in the direction of the particle's motion, particles act like they spin in the direction of your fingers -- left-handed particles act like they spin in the direction of the fingers on your left hand; right-handed particles act like they spin in the direction of the fingers on your right hand.
Kristin
What implications will Fermi Lab research have on our society?
Ken Bloom
I believe that any civilization wants to understand itself in a variety of ways. This can happen through the social sciences, history, and the arts. But we also want to understand our origins and our ultimate destiny, and that's what particle physics is about, in the end. I think we contribute to society by doing that. Thinking a little more practically, Fermilab does a lot of work in education. We also have physicists from many foreign countries doing experiments at the lab, so we are also promoting international cooperation. And maybe world peace, then?
Moderator
Thank you so much for all of your great questions tonight! You're making Chris and Ken think! The next chat session will probably be in the end of the March. Look for an announcement on Fermilab's website soon.
Roop
Why is kilogram not a unit of weight?
Ken Bloom
Weight is a force. When a massive body is in a gravitational field, it feels a force, and that force is called weight. So the kilogram is a unit of mass, and the force that it feels is its weight. On the surface of the earth, the kilogram has a weight of 9.8 Newtons -- the Newton is the unit of force in the metric system, like the pound is the unit of force in the English system.
KQ
Does the Z boson have an antiparticle?
Ken Bloom
Yes and no -- it is its own antiparticle!
Erol
Does your work take up alot of time?
Ken Bloom
Well, Chris and I found a couple of spare hours to answer your questions tonight! I would say that we do work pretty hard, but that's because we really enjoy what we do. The problems are often intellecually compelling!
PhysicsPhans
I don't understand the "gravity infinite" answer. If the field (and therefore force) go on forever, isn't that infinite even though it is very, very small?
Ken Bloom
Yes, I would say so.
Moderator
What is the Tevatron doing right now? Check the Tevatron status: http://www-bd.fnal.gov/servlets/d11?project=outside
Erol
Is there a possibility that there are particles that travel at the speed of light?
Chris Hays
All massive particles must travel less than the speed of light. It would take an infinite amount of energy to get them up to that speed.
Annie
What got you interested in being a physicist at Fermilab?
Ken Bloom
For me, it was largely by chance. I went to college at the University of Chicago, not too far away from Fermilab. I was majoring in physics and was looking for a part-time research job. I happened to fall in with a group that was doing research at the lab, and I liked it a lot. That was fifteen years ago, and the rest is history. As a graduate student, I did research at an accelerator at Cornell University in upstate New York, but I came back to Fermilab because of the exciting scientific opportunities here with the Tevatron, the world's highest-energy particle collider.
markDur
What type of a force is gravitational pull, and how close of a relationship does it have to magnetism?
Ken Bloom
Gravity is the force that one massive body exerts on another. Easily said, but why there is such a thing as graviational force we don't really know. Magnetism is a very different kind of force; it's related to electrical forces. Magnetic forces are typically much stronger -- just try picking up metal off the floor with a bar magnet. Gravity only seems strong because the earth is amazingly huge!
Don S.
Understood Chris, I'm beginning to get the picture. Can you help me understand the gravitational field associated with photons traveling at the speed of light? It seems reasonable to assume the warping of space time should not break the speed of light barrier, so will the gravitational field be "cone shaped" (I'm having trouble trying to frame the question).
Chris Hays
I think I understand what you are getting at. You can think of the gravitational field produced by the photons as ripples in spacetime, or gravitons, moving away from the photons at the speed of light. When you discuss the issue of photon radiation, you are discussing a quantum gravity effect, which is something that we still don't completely understand.
Erol
In Einstein's equation , E=MC^2 , why is the speed of light squared?
Chris Hays
The simple answer is that the units of energy are equal to mass times speed squared.
Don S.
Kind of tired tonight so I'll sign off early. You've given me much to ponder and I thank you for it. Best wishes and I'll be back next month.
mazz
does the language barrier ever make work more difficult
Ken Bloom
Surprisingly rarely. All of our scientific business at the lab is conducted in English, and in general those researchers whose first language is not English speak and write English very well. I wish I could speak Chinese as well as our Chinese collaborators speak English!
KQ
But don't some scientists believe in tachyons, which theoretically could travel faster than the speed of light?
Ken Bloom
I suppose some do, but I don't think there is any evidence for them.
PhysicsPhans
Ken: Can you explain a little more how a particle can be it's own antiparicle?
Chris Hays
An antiparticle is a particle with the same mass and opposite charge. If, in the case of the Z, the particle does not have any charge that can be negated, then the particle is its own antiparticle.
Guest
Generally speaking, how far into the future is mankind from developing a reliable means of controlling gravity? For such things is getting into orbit and maybe...beyond?
Ken Bloom
Hmm, if I could finally get that Atkins diet to work for me, then I could lose mass and there would be less of a gravitational pull on me. That would be one means of controlling gravity. But we don't anticipate any way of changing the strength of the gravitational force given a certain amount of mass, like the mass of the earth.
maverick
With LHC taking over the energy frontier in 2008/09 what will Fermilab's position to attract top notch physicists and engineers?
Moderator
Fermilab still has a lot of exciting physics going on, even with the LHC taking over in 2008/9. Between dark energy, extra dimensions, supersymmetry and who knows what else, I don't think that we will have any problems attracting engineers and physicists.
Erol
Is dark matter responsible for the expansion of the Universe?
Moderator
Theorists believe that dark energy is causing the expansion of the universe to increase.
maverick
As a follow-up to my previous question, is there any major upgrade planned
Moderator
We don't have any major upgrades officially planned yet, but there are many people that have start to lobby for the Next Linear Collider to be built at Fermilab.
PhysicsPhans
Thank you - Chris and Ken - for taking the time to help educate us. We hope you continue to find joy and excitement in your work.
Moderator
Thanks PhysicsPhan for joining us tonight! We appreciate all of your questions!
mazz
is it true that scientists got a piece of paper to change rooms by breaking down the particles and then putting them back together again kind of like in star trek
Ken Bloom
Haven't heard that one. There has been some interesting work in "quantum teleportation," in which an exact atomic state can be reproduced some distance away. But this has only been achieved a few atoms at a time -- we're nowhere close to doing it with human-size objects.
Erol
How do atomic clocks work?
Chris Hays
Atomic clocks have units of time measured by the frequency of their radiation. For example, the cesium atomic clock is induced to radiate energy at a well-known frequency, and by counting the cycles of the radiated energy, the elapsed time is measured extremely precisely.
Erol
What are those underground heavy-water facilities used for? it has something to do with neutrinoes.
Ken Bloom
Yes, those facilities are used to detect neutrinos, both from the sun and from distant supernovae, and maybe someday from accelerator-produced neutrino beams that are pointed in the right direction. Such large water tanks (although typically not heavy water) can also be used to look for proton decay.
KQ
So does that mean that another neutral particle, such as a neutron, would also be its own antiparticle? If so, then how come neutrinos are often referred to as having anti-neutrinos?
Chris Hays
The short answer is that neutrinos do have charge (the "weak" charge), and that neutrons are composites of charged particles that have antiparticle counterparts. The anti-neutron contains the antimatter versions of the quarks that make up a neutron.
maverick
If the decision making process is based on technical merit and physics why is there a need for a lobby and all the politics ?
Moderator
That's a tough question, Maverick. High-energy physics is very difficult to understand. When people come here, they can't actually see particles colliding. You can't see dark energy. Because all of this stuff is so difficult to understand, it takes a lot of effort to convince taxpayers to fund it.
Guest
Thank you for great answers during tonight"s session! am looking greatly forward to the march session!
Moderator
And thank you for participating!
Guest
How can you throw a projectile so that it has zero speed at the top of its trajectory?
Ken Bloom
At the very top of the trajectory, the velocity in the vertical direction is instantaneously zero. It may still have a horizontal velocity. To make that zero, it has to be zero to begin with, i.e. you have to shoot the projectile straight upwards.
Guest
Was light stopped?
Chris Hays
Light cannot be stopped when travelling in vacuum. Light can be absorbed by matter, at which point it is "stopped" by transferring its energy to matter.
maverick
Not to harp on the point, but it seems to me that a "good" connection could be made between the abstract pursuits of fundamental physics and benefits to society which would require the physics community to come together and reach some degree of consesus and thereby narrowing down the set of experiments
Moderator
In many ways, the global physics community is coming together to form common goals. The overall questions are where did the universe come from and where is it going? Each different experiment addresses these questions in one way or another. A great example of physics communities coming together is the InterAction collaboration. This is a group of communicators from almost every particle physics lab around the country.
mazz
does working at fermi lab help you get some ladies
Chris Hays
Oh yeah, become a particle physicists and the ladies will flock. It's the best recruiting tool we have, it's why *everyone* wants to be a particle physicist. Actually, there is a general perception in society that physicists are smart, and there is a certain kind of lady that appreciates and is attracted to that. But they're not always easy to find, and there certainly aren't enough ladies in physics.
Guest
Is particle physics like a box of chocolates? I mean you never know what you're gonna get.
Ken Bloom
I suppose it's true -- in a particular collision event, you can't predict what is going to come out of it. But we can make pretty good predictions on a statistical basis, i.e. what is the probability that we will see a specific phenomenon in any given collision.
Moderator
Chris and Ken are wrapping up their final questions now. Thanks again for participating tonight! Good night!
Guest
Could you tell me about the experiment you are working on?
Chris Hays
Ken and I work on an experiment known as the "Collider Detector at Fermilab" (CDF), which measures the particles resulting from high-energy proton-antiproton collisions. We are searching for new forms of matter and measuring the properties of recently discovered particles, such as the top quark.
Ken Bloom
Thanks for joining us tonight! You all had a lot of good questions, and I don't think I've typed this much in one evening since the night before my thesis defense.
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