Fermi National Laboratory


Questions and Answers from Virtual Ask-a-Scientist of March 19, 2002

More information about the program

Curriculum Vitae, Roger L. Dixon
Curriculum Vitae, Robin D. Erbacher

Moderator
Hi! Welcome to virtual Ask-a-Scientist! Roger and Robin are ready to answer all your physics questions. Fire away!


Carl
Roger, can you tell me a little about astrophysics?

Roger Dixon
Astrophysics attempts to use the knowledge we have of the way matter behaves at the very smallest scales-- quarks and leptons-- and uses it to understand the universe at the very large scales. Got any specific questions about how all this works?


Moderator
On this webpage you can see Live Events from the detectors of CDF and DZero http://www.fnal.gov/pub/now/live_events/index.html


Bill
How big is the tevatron? How much bigger will the new accelerator in Europe be?

Robin Erbacher
The Tevatron is approximately 4 miles in circumference. The LHC at CERN is 27km. One mile is 1.6 km.


Carl
I see that Fermilab is allowing easier visitor access. When will this be back to normal?

Robin Erbacher
Hi Carl, There is a press release right off of the FNAL website which explains the status. The good news is that we now allow pedestrians and cyclists into Fermilab without having to register. People in automobiles still have to request visitor's passes and arrive in the Pine street entrance, unless they want to go to the Lederman Science Center only. We hope that we will return to normal access soon, but we do not have a date.


BarbE
I noticed on Robin's CV that she is interested in - was it Top Quark? Is Fermilab working on quarks?

Robin Erbacher
Hi Barb, This is Robin. Yes, Fermilab scientists are working on studying many different quarks. The top quark is the heaviest of them all, and was discovered at Fermilab in 1995. We still have many things we'd like to learn about this quark, so we are busily sifting through the data as they come in!


Moderator
Recent Fermilab Press Release: Fermilab offers guided tours. (http://www.fnal.gov/pub/presspass/press_releases/guided_tours.html)


BarbE
Are there any quarks left to be "discovered", or are they all accounted for now?

Robin Erbacher
Well, all of the quarks that we have so far expected have been discovered, which we consider a great success for our models that predicted them. There may be something called squarks, which are the supersymmetric partners of quarks, but so far this has not been proven and is only a very elegant theory.


Moderator
On this webpage you can see Live Events from the detectors of CDF and DZero http://www.fnal.gov/pub/now/live_events/index.html


sri
What will happen to the Tevatron after the LHC goes into operation with the new upgrades ?

Roger Dixon
The Tevatron will probably continue to run after the LHC comes on. It will still have useful physics to do. However, there will come a time when we will want to replace it with a machine that will be more interesting and more competitive.

sri
Will that be the VLHC?

Robin Erbacher
The VLHC is a wonderful project, but very ambitious for the current technology. The US high energy physics community is now supporting a future Linear Collider, which would be an electron-positron colliding machine in the 500GeV-1.5TeV range. This is so far in the design and proposal stage, so we'll see what happens.


Barney
How are things progressing with NumiMinos?

Roger Dixon
The MINOS detector being constructed in the deep iron mine in northern Minnesota is progressing very well. It will be done well in advance of the beam, which is also progressing well at Fermilab, but a little slower. The detector should be finished by the end of 2003, I think.


Moderator
Fermilab publishes a bi-weekly magazine called FermiNews. On this webpage you can read the latest issue http://www.fnal.gov/pub/ferminews/ferminews02-03-15/index.html


KLHess
There was an article in the current American Scientist entitled "Is String Theory Even Wrong?" Any comments on this from Fermilab?

Robin Erbacher
Hi KLHess, That sounds like a very interesting article. Unfortunately, neither Roger nor I have read it, though now I plan to go look it up. Fermilab itself doesn't usually make official comments on articles. Do you have any specific questions that maybe we could answer about that?

KLHess
The author, Peter Woit, suggested that theorists are paying too much attention to a theory that "cannot be falsified by any conceivable experimental result." He suggests it's time to explore some alternatives.

Robin Erbacher
Hmmm. Some of my colleagues feel that way, too. :) Really, though, in my opinion (and everyone has different opinions on the subject) string theory is a very elegant mathematical model, and has been successful at achieving many things that we would like to see achieved in this science, such as Grand Unification. However, being an experimentalist, it is frustrating not to be able to search for strings!

Robin Erbacher
To follow up with KLHess question on the article, the theory of supersymmetry came from string theory, and we can (and in fact do) search for SUSY particles at our experiments.


Milosz
well i would like to know, what properties would an object have to exibit in order to be clasified as a black hole?

Roger Dixon
You would not be able to see it directly as no light can escape from it. You would see x-rays coming from the material that is falling into it as the matter is accelerated and torn apart. You would see evidence that there was a lot of mass in the area where you see nothing. In summary, it would be very strange behavior, and we do see lots of objects out in the universe that fit this description.


Moderator
On this webpage we post an accelerator update on a daily basis: http://www.fnal.gov/pub/news02/update.html

Moderator
Did you know that there is an exceptional variety of birds living, breeding on Fermilab grounds? Here is a link to our "bird pages": http://www.fnal.gov/pub/about/campus/ecology/wildlife/birds.html


puzzled
I can understand the repulsion between two electrons as the result of bombardment of each by virtual photons. But how does attraction between a positron and an electron work using the same virtual photon principles? Keep in mind that I'm not overly fond of falling back on "skyhooks" or mysterious fields as an explanation. Are the virtual photons between oppositiely charged particles 180 degrees out of phase so that when they interact they cancel out leaving the net force behind the particles and so they are "pushed" toward each other?

Roger Dixon
Good question. This one is difficult, The main difficulty is that you are trying to build up the attractive force between two particles by looking at just one tiny part of it. You have to remember that there are many interactions going on between the two charged particles and the net force is the result of all those interactions. It is not a single scatter. It is many scatters, and the net result is an attraction.

Roger Dixon
Also, remember that the virtual photons themselves can split into charged particles pairs and all of these get involved in the net interaction.


sri
What are the chances that the linear collider (if built) will be at Fermilabs ?

Robin Erbacher
Hi sri, Fermilab has endorsed pursuing the LC as the next major project here. It is a very ambitious goal. The German community is looking at a similar proposal called TESLA right now, and Japan is trying to write a proposal as well. Unfortunately, it is often a question of political support and willingness to be a leader in science around the world to make it happen. We only have some small amount of control over political decisions. But you all have a voice via your congresspeople!


Moderator
At Fermilab we have an education center called "Lederman Science Center". This is their homepage: http://www-ed.fnal.gov/ed_home.html

Moderator
QuarkNet is a research collaboration between high school students, teachers and particle physicists. This is the QuarkNet website: http://quarknet.fnal.gov/


Milosz
are there any projects going on (or planed), where users can volenteer their spare CPU clock cycles to help find new balck holes, and other objects in the universe (ala seti)

Roger Dixon
I am not aware of any such projects (other than SETI) which uses people's CPU's at home. Black holes are observed by x-ray satellites and ground based instruments, but those efforts always have enough computing power built into them. Much like Fermilab does not go to individual's cpu's to analyze our data.


Moderator
Fermilab gets a lot of physics questions from curious people. Physicists answer these question and they get posted on the Fermilab website: http://www.fnal.gov/pub/inquiring/questions/index.html

Moderator
On the Fermilab website you can find a High Energy Physics timeline, explaining who discovered what and when. This is the url: http://www.fnal.gov/pub/inquiring/timeline/index.html


puzzled
Is my view of the repulsive force between like charge particles to simplistic?

Roger Dixon
Well, not exactly. You view is basically right, but it is the subtleties of all virtual interactions that can go on to make the net force that is difficult to predict from basic interactions.


KLHess
The moderator is informing us of a number of what I would call "outreach" programs. Do you have an individual that coordinates such outreach activities? I have just completed year 1 of a pilot program I founded called Science Buddies. www.klhess.com/mentoring The program enables high school students to mentor middle school students (junior high in the Midwest) doing a science fair project. The students are backed up by professional scientists. If you have an outreach czar, I would be interested in contact information.

Moderator
I suggest that you get in touch with the Education Office here at Fermilab. Phone number is (630 840 3092.


Moderator
Fermilab is on 6000 acres of prairie and farm land. Here is a link to information about the restoration of the prairie: http://www.fnal.gov/pub/about/campus/ecology/prairie/back.html

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


MikeA
What is a Linear Collider? Is it linear as in a "straight line" or is it also circular, like the Tevatron?

Robin Erbacher
A Linear Collider is indeed in (more or less) a straight line. In some of the designs, the electrons are accelerated on one side in a straight line, and the positrons (antimatter electron) are accelerated on the other side, but the two accelerators are not exactly in a straight line. This saves real estate. But you can correct the beam positions with magnets in the final focusing. Electrons do better being accelerated in a straight line because if they go in a circle, they radiate away some of their energy in synchrotron radiation.


sri
Can Fermilabs produce and store antimater consitently and reliably. Do you forsee any commercial uses of antimatter in the near future ?

Roger Dixon
Fermilab produces and stores antimatter reliably for the collider. The quantity we produce is very small compared to what you would need to make a star ship, but people are beginning to think of commercial uses for it. I am only vaguely aware of these. Try searching for antimatter in the internet and see what you come up with.


Moderator
And to make the Fermilab animal story complete, I would like to inform you about the butterfly activity. A total of 51 species of butterflies were seen on the Fermilab campus during the past three years. http://www.fnal.gov/pub/about/campus/ecology/wildlife/butterflies.html


puzzled
Well can I generally assume then that whatever are the complexities of the total interactions, that the "attractive" force bewteen unlike charged particles is really due to a net propellant force toward the opposite particle which looks like an attraction but is really a propulsion toward each particle?

Roger Dixon
I don't know what you mean by "propellant force" but the particles are attracted to one another, and in principle, you can build that attraction up from the basic interaction between the two particles. You have to integrate over all possibilities to get the right answer.


Moderator
Back to physics. At this moment we have an exhibit called "Pulse - Accelerator science in medicine". We put it online: http://www.fnal.gov/pub/pulse/


phreak
Where are the electrons of a lightning bolt an instant before the bolt. Does their extremely high potential come from their being near each other??

Roger Dixon
I would state the reason for the potential in a little bit different way than you have. There is an excess of electrons in a different place than there is an excess of positive charge. This is what causes any electrical discharge or current to flow. Right before the lightening strikes the electrons are distributed in the clouds, air and ground a little more unevenly than they are when there when there is no threat of a lightening strike. This uneven distribution causes some strong electric fields that eventually causes the electrons to avalanch, or begin flowing in one direction. This becomes your lightning strike.


Milosz
How does the Fermi National Accelerator compare to the CERN counterpart?

Robin Erbacher
Well, CERN and Fermilab are similar laboratories in what their missions are, and in the scientists that work there.


Milosz
Let me restate that, how does Fermilab's accelerator compare to CERN's techinaly?

Robin Erbacher
Follow up to Milosz: For example, I could go and work at CERN because they are particle physicists just like me. And people who have worked at CERN come here as well. In fact, many scientists who have worked at LEP, the recently finished experiment there, are now working on the Tevatron here since the LHC is still several years away.

Robin Erbacher
Milosz continued: If you are referring to the actual experiments and machines, well that depends on which experiments you are comparing to. Earlier in this session I mentioned that the new project being developed at CERN (the LHC) is going into the LEP ring, which is 27 km. (1mile = 1.6km) The Tevatron is about 4 miles. But really the important thing is what kind of science are we doing. The LEP experiment at CERN used electrons and positrons, and made many precision measurements on the W and Z bosons. They also searched for new physics, like SUSY particles and Higgs. The Tevatron uses protons and antiprotons. The different methods can do different types of physics, so they are complementary.


puzzled
But I thought the photon (virtual or not) was the force carrier in EM reactions. How can an electron's photon reach out and "grab" a positron or proton? There has to be a physical action even at the sub-atomic level, no?

Roger Dixon
Yes, the photon is the force carrier, and virtual photons are responsible for the force between any two charged particles. All I have been trying to say is that one single interaction between a photon from one of the charged particles and the other particle does not necessarily lead to a deflection that brings the particles together. But, when you add up millions of these interactions with all the possibilities that can take place with the virtual photon, the net effect between two like-charged partciles is an attraction.


Moderator
On this webpage we post an accelerator update on a daily basis: http://www.fnal.gov/pub/news02/update.html


phreak
i have another one....If space is expanding why don't we observe the distance to say the moon, increasing??

Roger Dixon
The simple answer is that everthing we use to measure is expanding. So, how do we know that the universe is expanding? Because we see things moving away from us. And the light that comes from distant places in the universe is stretched out. We can tell this from absorption and emmission spectra, etc. Also, the effect between the moon and earth is miniscule on the scale of the Universe.


Moderator
Every year a Tornado and Severe Weather seminar is organized at Fermilab. This year this very popular seminar is on Saturday, April 13. Here is information about the program. http://www.fnal.gov/pub/news02/tornado.html


K. Michael
Do you have any videos on your website?

Moderator
Yes, we have VideoNews and streaming video of lectures and colloquia. Here is the url: http://www-visualmedia.fnal.gov/VMS_Site/s_videostreaming.html


Moderator
Virtual Tour: The next best thing to visiting Fermilab in person. http://www.fnal.gov/pub/about/tour/index.html


puzzled
OK, I think I'll follow up on this with a Saturday visit to AAS at the Lederman Center. A pad and pencil will add to the visualization. One further question, what actually defines charge, i.e. what is it about an electron that makes it negative and what is it about a positron that makes it positive? We toss these terms around as if they're givens, but I suspect there is more to it that would help with the explanation of attraction and repulsion.

Roger Dixon
Good idea on going to Lederman. Anyway, charged particles all emit and aborb virtual photons. It is always difficult to describe a properties of the particle by beginning with the fundamental emission and aborption of the photons. But the properties of this cloud of photons around the particle does determine what the other particle interacting with it sees and does. In the end you have positive and negatively charged particles. The charge is not defined by the cloud. It is defined by the way the particles behave, which, in principle could be determined form the virtual cloud if you were a lot smarter than me. Your question is really a good one for a theorist. They might tell you how to begin the calculation, and maybe even finish it.

puzzled
Thanks very much. You HAVE been helpful. I'll try these questions in more detail on your colleagues on Saturday. See you again.


phreak
Does the presence of a body( say an atom) affect the growth of the space it occupies or the space around it??

Robin Erbacher
Einstein's gravity (general relativity) equations do combine space with all of the matter around it, and does demonstrate these effects. However, we don't really know how to apply GR to things on the scale of the atomic size. Gravity is so weak compared to the other forces: 10^-41 times weaker than the electromagnetic forces. Particle physicists deal with very small particles, so gravity never comes into play. However, on the scale of planets and such, the GR equations become relevant.


Moderator
Fermilab publishes a bi-weekly magazine called FermiNews. You can sign up, it's free! Here is a link to the online version of the magazine http://www.fnal.gov/pub/ferminews/ferminews02-03-15/index.html Here is a link to the online subscription form http://www.fnal.gov/pub/ferminews/web_signup_fnews/sign_up.html


Carl
Do you guys do any weapons work there?

Robin Erbacher
Hi Carl, No, we do not work on any weapons here at Fermilab. We are specifically doing scientific research for a knowledge base in particle and astrophysics. Of course, along with that comes huge strides in technology, some of which can then be applied to advance society (examples: world wide web, superconducting magnets, accelerators in medicine, and on and on). Other Dept of Energy labs do work on weapons, but we are more like a giant university here.


Moderator
A short while ago we put together an online photo collection that introduces Fermilab in all its facets. Here is the link: http://www.fnal.gov/pub/about/whatis/picturebook/index.html

Moderator
What is the Tevatron doing right now? Check the Tevatron status: http://www-bd.fnal.gov/servlets/d11?project=outside


K. Michael
What's the difference between CDF and DZero?

Robin Erbacher
Hmm. Well, during the Tevatron Run 1 (~1986-1996) there was a much bigger difference. They were designed differently: CDF built in a large magnet and a tracking chamber, whereas Dzero built a finely segmented calorimeter. Both experiments produced a lot of very nice results, and together they discovered the top quark. Today for Run 2 the detectors are much more similar, although both have different strengths and weaknesses. We can look forward to very interesting results out of both of them. I would say that they are complementary, but we also need each other to combine our statistics so that we get more precise answers.


Milosz
i have a school debate about the big bang, i am split half way (it happened / it didn't happen) after seeing all the "evidence" for both sides, epecial hearing all the arguments that shot holes in what i belived about the big bang to this moment, if you could tell me one argument for the big band, that would explain why it did occur and how do we know that

Roger Dixon
There are two very strong pieces of evidence for the big bang. The first is the fact that all the other galaxies in the Universe are moving away from us. The second is that we see all the radiation that is leftover from the bang, and it has exactly the properties we would predict for it. So, there was a time when the universe was much, much, much smaller. Now if you ask a more difficult question such as was there really a singularity, you might get a good discussion going and find that there is some disagreement about what happened on the earliest and smallest scales.


david
I was just wondering in all the experiments involving CP Violation and the occurence measured for mesons was the velocity of the mesons ever measured, if not do you happen to know the velocities of Kaons and B-mesons

Robin Erbacher
Hi David, The velocities (momenta) of the various particles that are created in these experiments vary. We measure them with our tracking detectors in the experiments. We need to know the momenta so we can perform the necessary measurements. Of course, in the end we try to stop the particles in our calorimeters completely, so they give off their energy and we have a good measure of their energy. B mesons decay very repidly, though, so we usually see the daughter particles that come from them. We can then reconstruct the original.


Moderator
Fermilab has a big audience that visits the lab for cultural events. On this page you can see what we offer: http://www.fnal.gov/pub/events/culture.html


phreak
Is the modern science close to explaining gravitational force on quantum scale ( gravitons..). Is it such a big deal!??

Robin Erbacher
Good question. There are now very popular models for quantum gravity. I forget the title, but there is a very nice treatment of such ideas in a book by Andre Linde from Stanford University. Stephen Hawking always has nice treatments of such things as well. As far as gravitons go, this is the boson (force carrier) for the gravitational force. However, on the scale of subatomic particles, it is impossible to see gravitons or measure their properties (though we have quantum numbers for them) since gravity is 10^-41 times weaker than the electromagnetic force. There are several experiments that are trying and have tried to measure gravity waves. One is LIGO (CalTech is involved) and another is the Gravity Probe B out of Stanford, that is due to be launched (or has been launched... I have to check).


Hale_Bopp
Okay, I have a question about red shift that I have never really understood. We see objects moving away from us as red shifted. That means the photons have lost energy. What happens to the energy? Is energy not conserved in general relativity?

Roger Dixon
The answer to your question lies in the Einstein equation. Yes the photons have lower energy, but essentially, they have given it up to the expansion of the universe. Energy is conserved.


Moderator
Did you know that Fermilab had the second (or third) website in the U.S.A.? Read more about this: http://www.fnal.gov/pub/help/history.html


Rachel
I saw an article on the web today about a huge asteroid that zipped past earth recently, but went undetected for a few days because it came from the direction of the sun. How often does this happen, and what can we learn from these types of events?

Roger Dixon
Since I don't really work in that field, and we don't do that sort of astronomy at Fermilab, I can only answer you in general. Asteroids do zip by the come close to the earth quite frequently, and there are many asteriods that have not been found. We find new ones all the time. And, it is not only the ones that are coming toward us from the sun that have not been observed. It is just that it is very difficult to find and measure the orbits of all of them. An object that is 10 kilometers across is difficult to see, but it would do considerable damage to the earth if it scored a direct hit. You know, they might have to cancel the NFL preseason, or something.


Moderator
Fermilab maintains a good relationship with the neighboring communities. We often get questions from our neighbors. We answer and post them on our Community Forum website: http://www.fnal.gov/pub/about/community/forum.html

Moderator
A question some people ask us is "Why support science?". We devoted a webpage to the answer: http://www.fnal.gov/pub/inquiring/matter/whysupport/index.html


Milosz
the events of the big bang that happened at later times make sence to me, but the "something from nothing" theory as shown in our books, dosn't make a lot of sence to me, infact it makes as much sence, as the oposite view, that it was created by god in 7 days (adam and eve, etc)

Roger Dixon
The fact of the matter is, you can get back to a time when we don't understand what came before, or why it came. We keep pushing back as far as we can and so far, we keep getting more answers. This means that there will only be questions that can be answered by believing something. And we all do that-- even scientists.


Moderator
To get our protons on the way we use a "chain of accelerators". Here is more information: http://www.fnal.gov/pub/inquiring/physics/accelerators/chainaccel.html

Moderator
This is the website of Cryogenic Dark Matter Search, Roger's experiment: http://www.fnal.gov/pub/inquiring/physics/astrophysics/colddarkmatter.html

Moderator
And this is the website of CDF, where Robin does her research: http://www-cdf.fnal.gov/


phreak
Thanks to all of you guys...you have a wonderful site, too...best compliments!!!!

Robin Erbacher
Mieke, Kevin, and Judy et al of the Public Affairs Office deserve credit for the website. Mieke is the moderator here and Kevin is the ChatMaster. They are great. I have a lot of fun browsing through our site (when I'm not just going to the work-related pages). Thanks for joining us and asking such good questions!


Moderator
FermiNews, our bi-weekly magazine, features stories about Fermilab's experiments and the people that work on them. You can sign up, it's free! This is a link to the current issue: http://www.fnal.gov/pub/ferminews/ferminews02-03-15/index.html This is a link to an online subscription form: http://www.fnal.gov/pub/ferminews/web_signup_fnews/sign_up.html


Carl
What's the best thing about being a scientist?

Roger Dixon
Not having to worry about what you wear to work everymorning. Well, that's not really it. The best part is getting to work on answering some of the big questions about the world we live in and getting paid to do it. It is great to be a part of discovering something important for the first time.


Moderator
The Fermilab Education Office offers seven programs for under-graduate students: http://www-ed.fnal.gov/lasso/program_search/undergrad.lasso


Barney
So...What's the worst part of being a scientist?

Robin Erbacher
Hi Barney, Since I didn't comment on the *best* part of it, I'd say that I agree with Roger. It is really a great feeling to try to understand something for the first time, or to measure something that will progress the knowledge of humankind. However, being a scientist is very challenging in many ways. It takes many years to get to the level of professor or tenured researcher, and you gamble that you will eventually even get to such a position. You are often well into your 30s before you know. It also doesn't pay very much. But we do it for the love of our work. One of the more frustrating things, though, is the fact that our funding (and in fact funding for all of the physical sciences, surprisingly) has been cut constantly now, for more than a decade. We would love it if everyone out there placed as high a value on the work of science as we do, but it doesn't always happen. It's hard when you depend on the government for funding, and they keep changing their minds about whether or not they want to support you.


Moderator
Every Saturday afternoon, from 1 to 3 p.m., two Fermilab scientists answer questions at the Lederman Science Center at Fermilab. This program inspired us to go online and answer questions from people that can't come to the lab. Here is more information: http://www.fnal.gov/pub/visiting/tours/askscientist.html


Rachel
Is there any particular reason that Soudan, Minnesota was chosen for the location for the CDMS detector? Is there something special about that location other than the existence of the mine?

Roger Dixon
It was known back in about 1995 that the CDMS collaboration would need a deep site to extend the search for dark matter. They were setting up to run under the Stanford campus at that time. Meanwhile, Fermilab was planning to do the MINOS experiment in Soudan, so it was natural for the CDMS people to get together with Fermilab and plan to do the next phase of their experiment there. This way it was possible to take advantage of an existing laboratory and facilities. Which brings me back to Barney's question-- the worst part of being a scientist? That would be the coffee in Sadie's Bakery in Tower Minnesota-- that and having to go down in a hole and work all day when you are basically a mountain person.


Moderator
How much does your reseach cost anyway? The answer can be found on our Budget webpage: http://www.fnal.gov/pub/about/organization/budget_statistics.html


Spy
I read that lots of foreigners work at Fermilab. How do they all communicate? How do they get along?

Robin Erbacher
Hi Spy, nice icon! :) Yes, we do have a LOT of collaborating scientists from institutions around the world (and sometimes who are employed by U.S. institutions). It's wonderful! I have learned so much about other countries and cultures, and sometimes we meet in other countries to exchange information with physicists around the globe. We communicate in English: the official language now that is used at most conferences. At labs such as CERN in Europe, the official languages are both French and English, but conferences are typically in English. It used to be that German and Russian and other languages were very important as well, but now the default seems to be English. They are making it too easy for us English-speakers to get away without learning another language! But many of us who go to work at a lab in Germany or Japan or Switzerland will learn the local language out of interest and out of necessity to live in that society. It really keeps life interesting.


vv
i missed most of the chat and it might be answered already but from what i know dark matter is not an antimatter, so how these three (matter, dark matter and antimatter) coexist and why if matter is "balanced" by antimatter there is a dark matter too

Roger Dixon
Excellent question. I have been waiting for these dark matter questions. Anyway, you are right. Dark matter is not antimatter, but guess what? Dark matter is made up of dark matter and anti dark matter too-- well maybe. Since we are not certain what it is yet-- we haven't detected and studied it in the laboratory-- we can't be certain of this, but one of the favorite theories would predict this. In fact, one of the ways to detect it might be to see energetic neutrinos from the annihilations.

Roger Dixon
By the way, matter is not really balanced by antimatter in the universe. As near as we can tell, the universe is made up of matter and not antimatter. This has to do with almost all the matter in the universe annihilating and there being just a little bit of matter left over due to something called CP violation-- maybe. What was left over is what we see today.


Moderator
Fermilab's founding director, Robert Wilson, loved to sculpture and design. He greatly influenced the design of the entire laboratory site. Here is more info: http://www.fnal.gov/pub/about/campus/architecture.html

Moderator
Order Fermilab brochures online: http://www.fnal.gov/pub/about/public_affairs/brochures.html


mre1
i've heard it said that the "fabric of the universe" is bent/curved the closer one is to something with mass, like planets. what is the "fabric of the universe"?

Roger Dixon
The fabric of the Universe is spacetime, and yes, it is bent by matter. Surprisingly, space is not nothing. It is something that can be bent. Virtual particles pop in and out of it. It is actually fairly complicated, and we are just learning about all of its subtleties.


Spy
Hey Robin. Thanks for the answer. Sounds as if you really get to go places. Cool.

Robin Erbacher
Yes, travel is one of the "perks" of being in such a global field, but we also use a lot of email. Communicating with collaborators who are far away was one of the reasons the world wide web was developed at CERN and then at SLAC. But certainly nothing compares with going there and sharing information and designing things face to face.

Spy
... I need to run now. I'll be back, Spy


Moderator
Virtual Tour: The next best thing to visiting Fermilab in person. http://www.fnal.gov/pub/about/tour/index.html


Rachel
Why the need for the extreme cold temperature in the CDMS detector? Is this done in other detectors as well?

Roger Dixon
First of all there are other people trying to make similar "cryogenic" detectors. The reason the detectors have to be so cold is that we are trying to identify nuclear recoils that occur when dark matter, or WIMP, particles bounce off the nucleus. It turns out that one good way to do that is to measure both the ionization and the sound, or phonons, produced in the crystal when the nucleus recoils. To detect these very low level phonons the crystal must be very quiet, which means that you must bring all the motion as close to a stop as you can in the crystal. Hence the extremely cold temperatures-- 25 thousandths of a degree, or about 460 degrees below zero fahrenheit.


mre1
thanks Roger. so, when light exhibits wave-like behavior, is it the spacetime that is waving?

Roger Dixon
Spacetime is bent, or changes shape in a gravitational field. And, yes there can be oscillation, or gravitational waves in spacetime.


Moderator
A glossary and online resources for those who would like to know more. http://www.fnal.gov/pub/inquiring/more/index.html

Moderator
Physics questions from real people and physics answers from Fermilab scientists. http://www.fnal.gov/pub/inquiring/questions/index.html


mre1
i hear that sometimes light acts like particles, sometimes like waves. when acting like waves, what is waving?

Roger Dixon
The electric and magnetic fields are oscillating in a light wave. This wave behavior is governed by Maxwell's Equations.


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

Moderator
Live Tevatron Status shows the current status of Fermilab's Tevatron, the world's highest energy particle accelerator, and is updated every 10 seconds. http://www-bd.fnal.gov/servlets/d11?project=outside


Barney
Why is the Tevatron named the Tevatron?

Robin Erbacher
The Tevatron is so called because we are running at energies close to a TeV, or a tera-electron-volt. Electron volts is a basic unit of energy that we use: the amount of energy it takes to accelerate one electron over one volt. A tera would be 1000 times a Giga (you may be familiar due to the new PC capabilities), or a 1000 billion electron volts. The Tevatron is the highest energy accelerator in the world right now, so we are on the energy frontier. We hope that we can either see evidence for something new here, or even discovery something unexpected.


Moderator
"Is it safe to live near Fermilab" This is a webpage with answers to this and more safety questions: http://www.fnal.gov/pub/about/safety/index.html


mre1
i'm sorry, i'm not very mathematical. are the electric and magnetic fields associated with a particle? do they exist by themselves apart from a particle? do/can they exist independently from each other?

Roger Dixon
The electric and magnetic fields are coupled to the charges on the particles. Again, Maxwells Equations govern how all of this works. What I am saying is that the charges on the particles generate the fields and the motions of the particles cause changes in the fields.

Roger Dixon
Sort of.

mre1
Thanks Roger


aresnik
Could there be a communication medium (other than RF) that could work over far distances with low interference using minimal power?

Roger Dixon
Good question: In fact the Navy spent some money at Fermilab some years back investigating the possibility of communicating with submarines using neutrinos. This only satisfies the low interference over long distances part of your question. It takes significant power to create a neutrino beam, not to mention the problem of aiming it at a particular submarine that is moving around. Anyway, most of us at the Laboratory knew the answer to the Navy's question before they even got started looking into it, but they insisted. It is certainly possible to send a message using neutrinos. The problem is that it would take several days to transmit a simple message such as S.O.S. That is because you need so many interactions before you can be certain to get the contents of the message. That is what you pay for the "low interference" quality of your beam.
It is also possible to communicate with most all frequencies of the electromagnetic spectrum, but there is not a great advantage to taking this route although we have recently been using light in fiber optic cables. People also communicate with their television sets with infrared signals. You could also communicate with any kind of particle beam, but creating them is expensive and clumsy. It is not easy to change aim a high energy beam to any point you want to send a signal, so you are better off with low energy beams which don't go very far. In the end, I don't know how you would win at this game.


Moderator
It's 3 p.m., Fermilab time, and time to wrap up this chat session. Thanks to all of your questions. We all had a lot of fun! In about a week the complete transcript will be online, check the news box on the homepage or go to this url: http://www.fnal.gov/pub/inquiring/virtual/aas_transcript3-19-02.html Next month there is another chat, with different scientists, hope to see you again. Bye!

Back to Questions About Physics Main Page

last modified 5/10/2002   email Fermilab