Fermi National Laboratory


Questions and Answers from Virtual Ask-a-Scientist of September 22, 2003

More information about the program

moderator
Welcome to Virtual Ask-a-Scientist. I am Elizabeth Clements, of the Office of Public Affairs at Fermilab, and I will be your moderator for the evening. Our guest scientists tonight are Mike Albrow, Department Head of Fermilab's Experimental Physics Projects and Jodi Wittlin, of Fermilab's DZero experiment. And now we are ready for your questions.

Harvey
Hi.

moderator
Hi Harvey. Thanks for joining us tonight. We are ready for your questions.

Chem-Student
What is the DZero experiment?

Jodi Wittlin
Hi Chem-Student! The DZero experiment is one of the two main collision detector experiments on the collider ring here at FNAL. You can learn more about the specifics of our detector at the website the moderator posted above.

B-36
Why isnt my question being posted?

moderator
Hi B-36. Mike Albrow is working on your question right now. Your question will be posted with his answer.

B-36
If you accelerated a subatomic partice to a speed so close to the speed of light that its mass exceeded the Chandrasekhar limit, would it become a black hole?

Mike Albrow
No I'm afraid (or maybe I'm happy) that it would not. The reason is that if you could run alongside the particle it would appear to you to be going slowly, or even to be at rest. The physics has to be the same in each frame, so if it doesn't happen in one frame it won't happen when it's going very fast.

Harvey
What's it like to be a physicist at Fermilab?

Jodi Wittlin
Personally, I think it's great. FNAL is a wonderful place to be a physicist. I like being with so many other people who are physicists, and being able to interact with and learn from them.

Todd
What is the latest news in the search for the Higgs Boson?

Chem-Student
When I was reading the front page of the website, one of the questions was, "Can we create Black Holes in the Supercollider..." can you?

Jodi Wittlin
Well, without being "wishywashy", it's possible, but only under very specific circumstances, and only if certain theories are right.

Harvey
Why is there an Experimental Physics division? Isn't all you do experimental?

Jodi Wittlin
Actually, everything we do isn't experimental...we have a large theory group, as well as divisions for things like the beams production and the computing division.

B-36
Was that an answer to my question, Jodi?

Jodi Wittlin
Oh, I'm sorry..that was an answer to the Black Holes question... we're working on yours!

Ron
I must have been "dozing" but where did all the dark matter and energy come from?

Mike Albrow
You were not dozing when the dark matter and energy was created! The (exciting) fact is that although we are now very sure that dark matter and dark energy exist, and indeed form most of the universe (normal matter is about 4% only) we do not know what they are. Dark matter is probably very heavy particles that we have not yet made in the laboratory. Dark energy is a mystery but it is making the universe expand ever faster. Both probably came out of the big bang.

Mike Albrow
Hi Harvey, being a physicist at Fermilab can be terrific! Not only are we always doing new things, and looking at data that no one has seen before, but every week there are new things to be learned that other physicists do. It can be hard with long hours sometimes, but it is lots of fun and with lots of interesting people.

Todd
Sure, what is the latest news in the search for the Higgs Boson?

Jodi Wittlin
Well, we haven't found it yet, but I promise we're trying! Right now, both the CDF and D0 experimental collaborations are studying the data we've been collecting, and we'll keep looking through our data for hints of the Higgs.

Ron
I have much admiration for the people of Fermilab. You rightfully should be proud of what you are doing, you are at the top of the field (no pun intended).

Jodi Wittlin
Ron, thanks for that comment. I admire everyone here as well..it's an amazing group of dedicated people we have at Fermilab.

B-36
If you produced a photon with the right amount of energy, would it turn into a particle and its anti-particle?

Mike Albrow
Photons do continually turn into particle-antiparticle pairs, like electron-positron pairs, but if the photon is all alone they have to disappear again, they are called virtual electrons. It is energy and momentum conservation that prevents the virtual particles from becoming real. But if the photon passes close to an atomic nucleus for example the nucleus can give enough energy to make the particle-antiparticle pair real.

Balthus
Do you think you'll find evidence of the Higgs?

Jodi Wittlin
Do you mean here at FNAL or in general? I believe we will eventually find the Higgs, but whether it's at FNAL or at the new collider being built in Switzerland called the LHC, will depend on the physical properties of the Higgs, in particular, its mass.

Todd
What are the hints of the data that will provide evidence that the particle seen really is the Higgs Boson?

Jodi Wittlin
Todd, we'll basically comb our data for events we can't attribute to anything else, to start with. We also believe we understand enough about the Higgs to know how it's produced and how it decays... a "signature", if you will.

AaronB
I know that it is not directly related to high energy physics, but its close; Can compounds have Curie or Neel points above 1000*C?

Jodi Wittlin
Hi Aaron: Mike and I just consulted, and we're not sure of the answer to that...it's really solid state physics, which isn't our area of expertise!

Chem-Student
Have you actually attempted to create a black hole, is the idea purely theoretical, or are you afraid of the result of the experiment?

Mike Albrow
Big black holes, the sort you find in space (there is one in the center of our galaxy with a mass millions of times the sun's) are of course impossible for us to create (!!!) but there are theories in which space has more than three dimensions, with the extra dimensions tightly curled up much smaller than a proton. But in some theories there can be an extra dimension that is as big as 1/1000th the size of a proton (that's big for us). In that case there could be tiny black holes with a mass perhaps only 1000 x the mass of a proton. We might see these in our experiments and are looking. No sign yet! But don't worry if we do make some, they will immediately evaporate and not swallow up the earth!

bitthal
Do you think there is a fifth fundamental force?

Jodi Wittlin
As far as I know, we don't have any experimental evidence of one...

B-36
So all you'd have to do is blast enough photons into the vicinity of some atomic nuclei and you could make enough anti-matter for a bomb?

Mike Albrow
Antimatter bombs are probably impossible for a thousand years, although I should be careful about such predictions. Some physicists thought that a nuclear bomb would be impossible. However we have been making antimatter as hard as we can at Fermilab for years, and although we can make 100 billion antiprotons per day, in all the years we would not even have made a fraction of a gram! That's not much. Antimatter fuel for rockets is also totally unrealistic, unless someone can figure out a way to make it millions of times more efficiently than today.

brian
Have you seen any signs of the Higgs particle?

Jodi Wittlin
No, Brian, we haven't.

Chem-Student
Are there any particles that Fermilab or FNAL have discovered that are smaller than quarks and leptons?

Jodi Wittlin
No, Chem-Student, we haven't discovered any particles that are more fundamental (or smaller) than quarks and leptons, at least not yet!

Todd
So if the Higgs Boson is the carrier of mass, does that mean that all particles that have mass have the Higgs boson?

Jodi Wittlin
Todd, I'm not sure what you mean by "have" the Higgs Boson. The particles we know of aren't made up of Higgses, if that's what you mean.

Balthus
So what happens at Fermilab once the LHC starts running?

Mike Albrow
Fermilab will surely stay a top particle physics lab. For one thing we are heavily involved involved in experiments at the LHC, but there is also a program of physics to do at the Tevatron that is not the prime focus of the LHC experiments. I think there can be a very active program at the Tevatron for a few years more. Besides that there is an increasingly active program with neutrino beams, with two big experiments now and more to come, and some other experiments using particle beams. Some of us want to build a muon storage ring as a neutrino "factory" for more of these experiments. But in the longer term a large number of us would like to see a long straight electron-positron collider here. And in the VERY long term (25 years) a Very Large Hadron Collider, perhaps 5 times higher energy than the LHC.

bitthal
Can you describe the particle with 5 quarks?

Jodi Wittlin
The particle was discovered by 4 different collaborations and is named the "theta-plus"..it's made of 2 up quarks, 2 down quarks, and a strange anti-quark. You can read a journal article about it at www.cerncourier.com/main/article/43/7/1

ekphys
Hello! Checking in to see if any of my physics students had visited, actually! I visited in April of '02 and found FNAL quite interesting.

moderator
I'm glad that you had such a good visit. We have a very active crowd tonight, so some of your students might be logged on.

B-36
If you produced a photon with an energy of roughly 18,800,000,000,000 ev and sent it close to a group of atomic nuclei, wouldn't it turn into a proton and an anti-proton?

Mike Albrow
Yes it can do and sometimes does, but it is much more likely to turn into a "meson" made of a quark and antiquark, like a "rho" or "J/psi".

bitthal
Have you been able to or do you think it is possible to isolate a quark by itself at all?

Mike Albrow
People have tried very hard to kick a quark out of a proton and let it free, without success. It is almost certainly impossible, but theorists have not yet been able to prove that. So we keep looking, and there will be an experiment at the future LHC to look for free quarks. The idea that they are always trapped, never free, is called "confinement" and we would like to prove (or even more fun, disprove) it.

brian
What is the approximate mass of an electron neutrino?

Jodi Wittlin
Brian, the electron neutrino has a mass of nearly,but not quite, 0. Here's some info on neutrino masses and oscillations: http://www.ps.uci.edu/~superk/glossary.html

AaronB
Are there any particles, even theoretical, that are smaller than 1 Planck volume?

Mike Albrow
Nobody has too much idea about what nature might be like on a much smaller scale. The Planck scale physics is weird enough. I don't think it would be very useful yet to worry what happens below that. Space-time becomes foamy and disconnected in weird ways and perhaps particle become meaningless.

#1 Alex
In pertaining to Dark Energy, the universe is moving faster. Do you think this is because of negative mass? Or is there a 5th fundamental force we have yet to discover?

Mike Albrow
The universe seems to be accelerating faster because of dark energy, but it's still a mystery. Wheter it's due to negative mass or a 5th force I have no idea ... maybe something like that.

ekphys
What is the status/progress of the Neutrino project to the Sudan Mine in MN?

Jodi Wittlin
The Minos experiment is nearing completion. You can get an update on where they are at http://www.fnal.gov/pub/ferminews/ferminews03-06-27/p4.html

Lambdalana
Aside from their use in photomultiplier tubes, are photons used in particle physics?

Jodi Wittlin
We use them to identify types of particle decays in our detectors. Also high energy photons are used to probe protons and measure their structure.

cynic
What happens if the Higgs does not exist?

Jodi Wittlin
A lot of physicists go back to the drawing board to explain how it all works! It will be a very exciting time for us whether we find the Higgs or we don't.

B-36
What's the best possible efficiency you could get for making energy into anti-matter?

Mike Albrow
It's extremely small. Perhaps you can get an idea by saying (just rough numbers) our machines here use 50 Megawatts for 10 hours to make 100 billion antiprotons. Take the mass of those anti-p and convert to energy with E = mc2 and see what you get. I think you will find it is VERY inefficient, try it.

B-36
How can you have a subatomic particle composed of a quark and an antiquark? Wouldn't the quark and the anti-quark annihalate each other?

Mike Albrow
You are right! The quark and antiquark do annihilate each other, but that can take enough time for the particle (we call that a meson) to travel quite far. If moving fast some (pi meson) can travel 100's of meters before the q-antiq annihilate. Others travel mm, or even only about 10-12 = 0.000000000001 cm.

#1 Alex
What signs, if any, have you found for the Higgs?

Jodi Wittlin
There were some signs in 2000 that some of the experiments at CERN in Switzerland may have seen the Higgs. This was not convincing, however, and they could not claim a discovery.

Ron
How long can you store muons in a storage ring? I thought that they had a very short lifetime?

Mike Albrow
You are right, you can't keep them for long as they decay. But when they go very fast, within a sliver of the speed of light (99.9% c) time dilation (clocks run slow!) makes them live much longer. The much longer factor is Energy/mass. Then they can go hundreds of times round a storage ring before decaying.

cynic
What is responsible for most of the entropy in the Universe?

Mike Albrow
Nearly all the entropy in the universe is carried by photons. The microwave background is a big chunk of it. Starlight too. Only about one part in a billion of the total entropy is in matter.

Chem-Student
Are you guys not getting my questions or are you racking your brains trying to answer everyones questions:-)

moderator
Hi Chem-Student, We have a lot of good questions coming in. Our scientists are working on it right now. Thanks for being patient! :)

Chem-Student
Did you get my question? If a photon splits into its particle-anti particle pair near the event horizon of a black hole and one of the pair got sucked in but not the other what would that do?

Mike Albrow
I have got it now! The questions are flying in thick and fast! I can't keep up! One gets sucked in and the other can (it doesn't always, but it can) escape with more energy than the incoming photon. Energy is still conserved, the black hole gets a tad lighter.

Todd
If we have enough information about the Higgs to know its signature, what is keeping us from concluding that it exists? Is just a matter of building larger accelerators or more accurate detectors?

Jodi Wittlin
Todd, we simply haven't seen the signature distinctively.... The Higgs is a hard particle to find! It's like looking for a needle in a haystack, so we're working on both making the haystack bigger (by building larger accelerators AND by taking more data with the one we have) and by making more precise detectors and using the detectors we have in new ways.

Lambdalana
Is a photon a baryon or a lepton

Jodi Wittlin
Photons are neither baryons or leptons! Check out the particle physics glossary at http://www.particleadventure.org/particleadventure (along with some other interesting particle "stuff"!)

Cinder
What does it mean that the Higgs boson is the "carrier of mass"?

Mike Albrow
Hmm. Tricky! It is impossible to explain the Higgs in a few sentences, but: An electron in your little finger and an electron in the little toe of a creature in the Andromeda galaxy have exactly the same mass!!!! Wow!! How do they know what mass to have? What links them? In this theory there is a field throughout the universe (the Higgs field) and all particles interact with it. Sometimes one can think of the field as some sort of resistive medium ("molasses") that stops the particles travelling at the speed of light, which they would if they had no mass. Or a crowd of people that slows down someone trying to walk through. But it's not a great analogy because the Higgs field does not slow down the particles, it just gives them resistance to acceleration. Electrons, muons, quarks, all couple differently to this H field, and that gives them different masses. That's the best I can do in a few minutes.

Gdutch
Have you found any evidence of the Higgs particle?

Jodi Wittlin
There were some signs of the Higgs in 2000 at CERN, but we haven't seen it here yet.

moderator
You are all asking great questions! You are certainly testing our scientists' typing skills!

neutrino
I have been told that bosons are "the force carriers" but am still unclear as to what they actually are.

Mike Albrow
Among all the fundamental particles we know, there are two classes, one (fermions) with spin (in some fundamental unit) 1/2 or 3/2 and some with spin 0 or 1 or 2. Spin 1/2 are called matter particles like electron and quark (also proton but that is composite, not fundamental). Spin 1 particles are swapped or exchanged between these to bind them together or push them apart. These are photons, W and Z bosons (weak force) and gravitons (spin 2), quanta of the gravity field, not yet detected. The Higgs is also a boson, spin 0, not yet detected, but will give rise to a force between particles of matter.

moderator
Need to learn more about particle physics? Go to http://www.interactions.org

cynic
How is Fermilab able to put protons and antiprotons in the same accelerator and not have them colliding all the time?

Mike Albrow
The accelerator is 4 miles around. The protons and antiprotons are kept in 36 little bunches about 60 cm long and less than 1 mm in diameter. As the bunches counter-rotate they are steered to avoid each other everywhere except at the two places where the experiments are. So they only annihilate where we are interested in seeing the collisions.

DAMTP
Could you address the question: Can the weight of the Higgs particle be accurately predicted based upon current data?

Jodi Wittlin
It can't be "accurately" predicted, but current data and models give us a range of masses where we can expect to find the Higgs.

B-36
Is it possible that the quantum foam has a surface tension and that that explains why general relativity is innaccurate at the subatomic level?

Mike Albrow
That's really into unknown territory. General relativity will break down at the quantum foam (Planck) scale because spacetime is not at all smooth there, and the topology not well defined. Surface tension probably has no meaning on this scale.

neutrino
Is it possible that there is mostly matter rather than antimatter in the universe as far as we know because of some process similar yet opposite to what is being done at Fermilab to create antimatter?

Mike Albrow
At Fermilab (and other such labs) when we create antiparticles we create an equal number of particles. We do not know how the universe we see became nearly all matter. There are several ideas, but none have been tested in the lab so we really don't know yet.

Lambdalana
Mike could you explain to me why nearly all the entropy is carried by photons?

Mike Albrow
Entropy is given by counting the number of possible states. For every proton in the universe there are about 1000 million photons, so they have most of the states.

#1 Alex
What has been the most exciting experiment for you to work on?

Jodi Wittlin
I find being on D0, here at FNAL on the energy frontier, to be the most exciting experiment I've been on! But my previous experiments were pretty interesting and exciting as well.

Chem-Student
If one of the pairs of the particle-antiparticle photons escapes with more energy than the first then how does the energy transfer from the particle that is getting sucked in?

Mike Albrow
Tricky, but it's as if the particle getting sucked in has negative energy. In such strong gravity fields strange things happen!

DAMTP
In some literature the Higgs boson has been postulated to be the heaviest particle so far "found"- any thoughts? Thanks

Jodi Wittlin
I haven't seen any literature claiming to have truly "found" the Higgs...only to have found evidence of it. Until we have a definite mass for the Higgs, we can't say whether it's the heaviest fundamental particle, or not. But it is quite likely to be lighter than the top quark which we found to be about 180 times heavier than a proton.

neutrino
Is it possible that there were in fact two universes created in the big bang, and ours was made of matter and the opposite of antimatter? If so could black holes be a sort of "go between" between the two. What do you think of this theory, and what do you have to say about it?

Mike Albrow
I have a warm feeling for that idea as I actually wrote a little note on it back in 1970 (yes I'm old). Like Universe-antiuniverse pair creation. It was neat but it never caught on. Part of the reason is because there is no way of testing it, there were no clear testable predictions, so many said it was not real science. Which is true. However for your idea that black holes might connect the two, would one be a "white hole"? That would destroy the symmetry. It's fun to think about it, but if you can't test it it's rather beyond physics.

Guest
How long does a particle take to make a full cycle around the collider?

Jodi Wittlin
A single particle can take nearly 50,000 laps of the Tevatron in a second!

neutrino
How exactly do bosons, the photon for example, "carry" forces?

Mike Albrow
Hmmm. Imagine two ball players running along exchanging a ball. That keeps them close. The heavier the ball, the closer they must be. A photon has no mass and the players can be far far away (the electromagnetic force has infinite range). The W and Z are very massive and the range of their force is much smaller than the size of a proton.

Gdutch
Has Fermilab detected any evidence of the five-quark particle that was discovered in other laboratories?

Jodi Wittlin
No, we don't have an experiment here at FNAL looking at this state, but you can read about the experiments that did it at http://www.cerncourier.com

neutrino
how do bosons, higgs and gluons for example, affect the other elementary particles?

Jodi Wittlin
Gluons and the higgs act as force carriers...so you can see Mike's explanation of those right above this to get an idea. The act to carry forces between different particles

Gdutch
If the universe is speeding up, what are the possible causes? Is there any evidence to support the theories of dark energy, antimass, or even a fifth fundamental force?

Mike Albrow
We don't know why its speeding up, we call it dark energy but don't yet know what it is. But there is evidence from the microwave background ... look up WMAP on Google! - about half the energy in the universe is dark energy.

Sue
I am a Middle School Science teacher. My students all do Science Fair Projects to enter in local, regional and state fairs. I have an 8th grader who is interested in doing a high energy physics experiment. Would someone at Fermi be willing to talk to him

Jodi Wittlin
Sue, the best people to answer that would be the ones in the Fermilab Education office...they have resources and information to help your student. Check out http://www-ed.fnal.gov

Guest
Did you get my questions about the neutrino? Its best estimated mass and its oscillatory period?

Mike Albrow
We think there are three different mass neutrinos. We cannot yet measure their masses but they are very small, like less than 1/1000 the electron mass. It is easier to measure mass differences and we are doing that here, Japan and elsewhere. The oscillatory period depends on its energy, experiments are being done to measure all that.

cynic
How is Fermilab able to keep protons together? If they all have the same charge, why does the beam not explode

Jodi Wittlin
Cynic, accelerators take advantage of the way magnets and their fields interact with charged particles to "herd" the particles together. By putting together different sets of magnets, the accelerator physicists can "focus" the beam...just like you might focus light through a lense.

Guest
Hmmm... in your response to "Cinder", the Higgs Field sounds like the "ether". I suppose there is a good reason to think otherwise?

Mike Albrow
Well it sound a bit like the ether idea but in that idea the light waves were oscillations in the ether and so the speed of light depended on your movement through the ether. It did not so that idea was killed. With the Higgs field it's different, and no experiment can detect a motion through the field. The speed of light is the same in all frames. However interestingly there IS a preferred "rest" frame in the universe. It is that frame in which the cosmic microwave radiation looks the same (same temperature) in all directions. So the Earth is moving through that MW bath at some speed, I don't know but it's something like 200 km/sec I think. Don't quote me, look it up.

neutrino
What exactly is the oscilitory period and how does it pertain to elementary particles?

Jodi Wittlin
An oscillation period is the amount of time it takes to go from one state to another, and then back again. Think of tennis...it's the amount of time it takes for you to hit the ball to your opponent, and then get it back. It pertains to particle physics because particles can in fact oscillate between states...that's a subject close to my heart, because I wrote my PhD paper on measuring the oscillation of one type of particle into its anti particle, and then back again!

neutrino
How exactly do bosons work?

Mike Albrow
They sit at their desk in front of a computer terminal!

Guest
What is the best possible efficiency for converting energy to matter?

Mike Albrow
Already answered. It's tiny.

cynic
How many years does it take to become a particle physicist?

Jodi Wittlin
It depends how you define a particle physicist...if you mean how long does it take to get a PhD in particle physics, it takes most people 6-8 years after they finish their Bachelor's degree to get a PhD.

scisarah
How much mass are they thinking neutrinos have now?

Jodi Wittlin
They're very light...less than 1/1000th of the mass of an electron, or 1/1billionth of the mass of a proton!

Cinder
If fundamental particles are pointlike, how do they "collide"?

Mike Albrow
Good question. The short answer is "not head on". When two electrons collide they must have some miss-distance, but they still exchange photons and scatter away. The same with quarks. Protons and antiprotons have size, but the quarks are point-like at any scale we can reach. If they pass by VERY close thay can scatter out through a large angle and we see this, well not the actual quarks but particles they produce, and can deduce that the quarks are smaller than 10-18 cm (0....18 zeros ... 1)

scisarah
I'm glad someone asked about the Higgs.

Jodi Wittlin
I am too, since I'm part of the group searching for the Higgs on D0!

neutrino
Is it possible that neutrinos are both matter and antimatter? Then would it be poosible that there is a quark equivalent of a neutrino and that quark equivalent was both matter and antimatter.

Mike Albrow
There are neutrinos and antineutrinos, matter and antimatter types. Similarly there are electrons and antielectrons and quarks and antiquarks.

Gdutch
Has Fermilab performed any experiments on isolating quarks, and if so, what were the results?

Jodi Wittlin
Yes, we've been looking for isolated quarks, but we haven't found any... the LHC at CERN will also look for them.

cynic
How much entropy does a black hole have?

Mike Albrow
I can't give you a number off my head, but the entropy of a black hole is huge and proportional to its surface area. In fact in some String theory it is equal to the total number of string states that can fit on the surface. Huge! Stephen Hawking first said about the BH entropy, but the business about the number of string states is recent.

Guest
Thanks alot for your time!

Mike Albrow
You are welcome, it's a pleasure, but my fingers are aching from all this typing. Learn to touch type! Mike

scisarah
Any recent developments on black holes? Maybe in conjunction with particle physics?

Jodi Wittlin
scisarah, there have been some interesting discoveries about black holes in astronomy lately, but they haven't really been related to particle physics.

Sinh
I read in the textbooks that Michelson Morley experiment made Physicists discard the Aether notion. Einstein then presented his special relativity. It is funny that Physicists refuse to accept the existence of Aether, but accept the idea of space contraction, a kind of Aether, I think. What do you think about that?

Mike Albrow
The ether as a medium in which light waves propagate was discarded and never found to be useful (or correct) since. Einstein made spacetime an arena for physics that can do things like be bent (by mass or energy) and apparently distorted by changing your motion. This is different from the ether idea.

scisarah
Is red shift the primary way you guys can find black holes?

Jodi Wittlin
scisarah, there are number of ways to look for black holes, but that's really what astronomers are doing...we only look for black holes if we accidentally make one in our accelerators, not on purpose!

Guest
Is it possible to create a black hole in a particle accelerator?

Jodi Wittlin
I think we addressed this a bit earlier this evening...the answer is maybe! It depends on which theories of physics are right, and which aren't. We're always on the lookout for them, though!

neutrino
What exactly is quantum foam?

Mike Albrow
Exactly is a strong word and I cannot say. But the idea is that if you look at spacetime on small enough scales, close to the Planck length, it is no longer smooth, but gets full of holes (hence foam). These holes are actually black holes (and white holes?) on a miniscule scale. Reason? Energy fluctuations allowed by the Heisenberg Unceratinty Relation become so HUGE they can actually deform spacetime into black holes. We do not know if this actually happens because there are no experiments, but it's about the best idea we have.

neutrino
What is the smallest particle ever?

Jodi Wittlin
As far as we know, all "pointlike" particles...electron, taus, neutrinos, quarks, etc. are equally small.

neutrino
Is it possible for anti annihilation to occur?

Mike Albrow
Well, an antiparticle and its particle can annihilate into "energy", and that "energy" in the form of a photon can turn back, so this is like anti-annihilation. We call it pair production.

Sinh
Gravity field bends light ray. Does elctric field bend light ray. If not, why?

Mike Albrow
Yes, all energy bends light rays. But the energy in an electric field (at least, any we can conceive of) is much too small for any bending to be visible.

Sinh
What happens for an electromagentic wave if it travels in a superconductive waveguide?

Mike Albrow
The superonducting waveguide will reflect the wave perfectly and you will have a waveguide without attenuation.

moderator
We have about fifteen minutes left. Please submit your final questions now. This has been our most popular chat session so far. If your question did not get answered, check back in a week or so for the transcript. Mike and Jodi will be able to answer any missed questions after the session is over, and they will be posted on the transcript.

Sinh
Why the velocity of light is a constant in space?

Mike Albrow
This is a why question and most why questions like that cannot be answered. Actually it's the speed of light that is constant in space, velocity has direction and can be changed. But I know what you mean. All experiments agree with the hypothesis that is is constant and we believe it to be true until proved otherwise. Don't ask why ask how!

Sinh
Going further in General Relativity, Einstein said that space can be bent! If we do not accept space as some thing other than "absolute vacuum- complete nothingness", how can we imagine we can bend some "nothing"?

Mike Albrow
Space and the vacuum is not really "nothing". It has shape. It also happens to be full of virtual particles and dark energy and stuff. There is no longer any "nothing" in physics.

Guest
Thank you all, until next time.

neutrino
Is it possible that most black holes actually are not the incredibly large ones, but rather miniscule, and if so how can they have zero mass, and/or size?

Jodi Wittlin
It's certainly possible that some, or most, black holes are smaller than what we think of as "black holes in space", but they can not have zero mass.

neutrino
How can particles exist if they are points, which would then make them infinitely small and therefore how would distance apply? l

Mike Albrow
As far as we know these particles have no size, but if you zoom in to much tinier distances they may look like little strings. The concept of distance may apply at that scale scale or not, but they still exist. Who told you something has to have size to exist? But I expect they do at a much smaller scale.

Sinh
I think the number of "quarks flavors" as 6 is somehow connected with the number of "space dimensions", currently forwarded by many Physicists.

Mike Albrow
It is certainly POSSIBLE that the number of quark flavors is related to the number of space-time dimensions. But nobody has yet figured it out.

moderator
Physics is our mission, but buffalo may be Fermilab's main attraction for visitors. What are buffalo doing at a physics laboratory? Here is the answer: http://www.fnal.gov/pub/about/campus/ecology/wildlife/bison.html

Jodi Wittlin
You know, I actually really like the buffalo here at FNAL. The baby ones in the spring are actually pretty cute!

moderator
The buffalo are very cute. Every spring about 30 or so bison are born. They are very popular with the local community.

Jodi Wittlin
I think it's experimental evidence of how diverse the science is at Fermilab...we have bosons, and buffalo!

moderator
Indeed! Bosons, buffalo and butterflies - oh my!

neutrino
Can a wavelength be infinitely small and/or infinitely large?

Mike Albrow
The wavelength can in principle be enormous (not infinite, but one might imagine galaxy-size) or tiny (but not infinitely small ... let's say a few planck lengths.)

cynic
What is the final state of the Universe?

Mike Albrow
Many possibilities. It could expand for ever, all the protons decaying, all the stars collapsing and decaying or turning into black hoiles, all the black holes will eventually evaporate. All you will be left with is photons, electrons (one per cubic light year and decreasing, neutrinos with enormous wavelengths,, and cold cold cold cold. Or it could crunch back to a collapse, but we don't think that.

Josh
Here's my idea for making the anti-matter for an anti-matter bomb: Blast photons with the correct energy for making the subatomic particles that comprise atoms into chambers. These chambers would have air in them so there would be atoms close by from which energy could be drawn so these photons could turn into subatomic particles. You could use one chamber to make each of the subatomic particles that comprise an atom. Antineutrons might be more difficult to control because they have no charge. If so, what you could do is make the antiquarks that comprise antineutrons and combine them into antineutrons later. According to my calculations, if you could achieve 10% efficiency and you doubled the power output of the United States and used all the extra power for making the anti-matter bomb, you could produce enough anti-matter for a 1 gigaton bomb in 3.134 years.

Mike Albrow
My first response is: Why would anyone want to make an antimatter bomb? We have far far too many huge weapons as it is. Don't even think about it. Now to the physics. Fermilab makes more antimatter in the form of antiprotons than anywhere else on earth. We make about a million million on a good day. Still if you ran it with 100% efficiency all day and all night, and could collect all the antiprotons you made, it would take over 10,000 years to collect one gram. ONE GRAM! That's 1 million years to get 100 grams, a few ounces. Then you have to make the antiprotons combine with positrons to make a neutral atom, antihydrogen, otherwise they all repel each other. That is very difficult. We have succeeded with great difficulty in doing it for a few thousand anti-atoms. But they immediately hit the walls of the vacuum chamber and annihilate. You have to find a way to keep them, which is very very difficult. In principle one can think about some form of "magnetic bottle". Even if you could do that, I cannot imagine that you could keep any more than an extremely dilute gas of a few or a few hundred atoms. We have not done it with hydrogen yet, and antihydrogen will be even much harder. So I am delighted to tell you that no-one on earth will make an antimatter bomb for a thousand years, maybe for ever, and I hope I'm right. Also, you can completely forget about antimatter powered rockets, for the same reasons. Forget it.

Guest
What would have a wavelength of a few plancks?

Mike Albrow
The Planck length is roughly equal to 1.6 x 10-35m in the Standard Model. In models with extra dimensions of space it can be much bigger. In "superstring theories" one can imaging "particles" as "superstrings" with wavelengths of this order. But as spacetime becomes sort-of "frothy" on the Planck scale it is not clear that wavelength has much meaning there.

cynic
If a particle has no size, how can it have a spin?

Mike Albrow
Good question! Do not think of a particle as a spinning ball, of course not if it has no size. What a particle really has is the quantity called "angular momentum". Angular momentum is a directed quantity (like the Earth has a rotation axis) but not a vector, it's called a "spinor". So an electron's angular momentum is a spinor ... put it in a magnetic field and its spin can point either along (UP) or against (DOWN) the magnetic field but in no other direction. It can also be in a state which is a mixture of up and down, like 60% up and 40% down. In quantum mechanics particles are weird and not like balls, there is no surface or pole or equator, it's just a point with angular momentum!

Sinh
Electric field is stronger than gravity field. Electric force is stronger than gravity force. Then why the bending of space caused by E field is smaller that the bending of gravity?

Mike Albrow
Gravity adds up because it does not have + and - charges like electricity. So every proton, neutron and electron in the whole Earth adds up to make the Earth's gravity which gives a warped space time which is still quite small in some sense. But the Earth has about no electric field because every electron charge is cancelled by a proton's charge. Gravity IS bent spacetime (don't say bent space, it's bent spacetime). Still, if you have an electric field, the electric field has energy and everything with energy bends spacetime, ie causes gravity. But the effect is so small it would be very, VERY hard to detect.

Sinh
What creates the field of gravity or electric field, that means what supplies the energy for those fields? We can say that mass and charge are the causes of those field, but I think mass and charge are actually the measure units of such fields, not the causes of such fields. For example, if we say we have three dollars, we can assign the idea that we have a mass of three (dollars). But a number three does not make dollars! What do you think?

Mike Albrow
The gravity field IS caused by mass or rather Energy-momentum, and the electric field by charge or a changing magnetic field. Don't say mass is just the unit measure like dollar a unit of currency. Currency is currency no matter what the unit, and mass is mass whether it's ounces or grams. Once a field is there you don't need to "supply" energy to keep it there.

Guest
Einstein's Cross - please address as part of the matter-antimatter question of a co-universe- any relavence?

Mike Albrow
Einstein's Cross is (probably) a quasar, the light being bent by the gravitational field of a galaxy it passed by, so the cross shape is an illusion. This has no relevance to antimatter and nothing to do with a co-universe.

Sinh
If we accept that we and matter are "local light waves in Aether" and a local reference frame is made by light wave, then the speed of a reference frame in Aether is caused by contraction or change of wave in Aether, will it explain why the light velocity is the same in all reference frame and the time dilation effect too?

Mike Albrow
We and matter are not "local light waves in Aether" and a local reference frame is not made by light wave. And by the way, light velocity is NOT the same in all reference frames, but light speed is. (Velocity has direction, speed is just a number.)

moderator
Thank you everybody for participating in tonight's session. You all asked very good and challenging questions. Be sure to check back for the transcript! Goodnight!

Jodi Wittlin
Good night everyone! I hope to see you visit us at Fermilab sometime in the future!

Mike Albrow
Good bye everybody around the world from Mike at Fermilab.

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