Fermi National Laboratory


Questions and Answers from Virtual Ask-a-Scientist of November 18, 2003

More information about the program

Moderator
Welcome to Virtual Ask-a-Scientist! Harald and Greg are ready for your questions!

Student
Why do certain particles not have spins whereas other particles do?

Greg Davis
Quantum Mechanics tells us that if a particle can spin, it will. The only particles with no spin are particles that are the same in all directions, like points or spheres.

sci123
What are stars made of?

Harald Fox
Stars go through a whole evolution. They start of just gathering all the material in their vicinity through gravitation. The material they consist of in the beginning is almost only hydrogen. But as stars heat up when the matter is crushed together fusion starts and the star fuses hydrogen to helium. Later in the live of a star when almost all the hydrogen fuel is burned heavier elements are being produced. The star slowly builds many elements up to Iron. Heavier elements can be produced by the death of a star in a supernova.

Student
In theoretical physics, what is the "baryon decuplet"?

Greg Davis
I think the baryon decuplet are the ten ground state baryons that can be made from just up, down, and strange quarks. If you lay them out it forms a triangle. This is not something we think about much anymore, though it was important for coming to understand the quark model.

Cinder
Is the Tevatron still in a shutdown?

Greg Davis
The Tevatron is still shut down, but will be up again in about a week.

sci123
What is the tevatron?

Greg Davis
The Tevatron is the world's highest energy particle accelerator. It creates proton-antiproton collisions with a center of mass energy of 1.96 TeV. It is nearly four miles around.

Student
What is the "meson nonet" in theoretical physics? Is it a method of classifying mesons?

Harald Fox
Similar to the decuplet, baryons consist of 3 quarks, mesons of 2 (quark+antiquark). If you build the possible combinations out of the low mass quarks you end up with these combinations of 8, 9 or 10.

BentArm
I saw a show on PBS the other day with a scientist from Fermilab. Can you tell me what work Fermilab is doing regarding String Theory? I don't really understand the connection.

Greg Davis
String theory makes predictions about particle interactions at energy far beyond what we can achieve today. If Fermilab had a much bigger accelerator - many thousands of times bigger - it would be obvious if string theory were true. However, the theory does make some subtle predictions about interactions at our energy, and we are looking for those signals.

sci123
If strings exist, what do they give off?

Greg Davis
If string theory is true, then all fundamental particles are strings. This means a string would give off and absorb only other strings.

BentArm
Thanks, Greg. Is there any relationship between the Higgs Boson and String Theory?

Greg Davis
Most of my colleagues are convinced the Higgs must exist, but are not very confident about string theory. As far as I know, the Higgs is consistent with string theory. If there is no Higgs Boson, then a great deal needs to be re-thought, and that might include string theory. I am not sure.

Charlie
What would we see if we were traveling with the speed of light?

Harald Fox
When you travel at the speed of light or just below it time gets dilated. So for the rest of the world your lifetime becomes longer. We can see this in cosmic rays. Particles that normally don't live long enough to make it through the atmosphere to the surface of the earth actually do because their lifetime increases. In the limit of traveling at the speed of light everything would happen at an instant.

sci123
If we could tear the space fabric, how would that create a wormhole?

Greg Davis
I am not sure I understand the question. Spacetime can have singularities, and it probably does. What happens to a person who hits it, is unknown. The most likely answer is simply destruction, but some cool theories suggest these are wormholes that take you to another place. A singularity - usually called a black hole - is created when there is too much mass in too small a place.

Student
Why do neutrons decay when they are in isolation?

Greg Davis
Because a proton plus an electron plus a neutrino are a little bit lighter, and it is allowed. Feynman said, "That which is not forbidden is mandatory." Eventually the decay must happen.

Brutis
What is gravity, and do all things including comets have gravity?

Greg Davis
Comets certainly do feel gravity. Every particle with energy, including the atoms that make up comets, feels the pull of gravity.

BentArm
What about the LHC? Will it find the Higgs? If so, what about Fermilab?

Harald Fox
The LHC at least has a pretty good chance to find the Higgs! Theory and measurement both prefer a relatively light Higgs boson. The LHC detectors are designed to search for the Higgs in that region. So if the Higgs has some resemblence to what we think it is there is a good chance that it's found at the LHC. The highly active regions in high energy physics move back and forth. A few years ago CERN with the LEP experiments was a fascinating place to be. While CERN is preparing for the LHC the hot spot is Fermilab. When LHC is running Fermilab has the challenge and the chance to prepare for the future. It may be neutrino physics; it may be B-physics; or it also may be the Linear Collider that is discussed in the community.

sci123
Is there any difference in the disasters that happen when two atoms collide and when an atom is split?

Greg Davis
I don't generally think of processes of particles as disasters. Large atoms are too big and so under the right circumstances they will split. Some, like U235, are so unstable they will split spontaneously and give off energy. Other atoms are smaller than is ideal and will join together and give off energy. Those that are smaller than iron can fuse together and those that are larger can split. In either case, they give off energy. To create these large atoms requires putting energy in.

Charlie
Since the effect of time dilation also takes place in the event horizon of a black hole, we can assume that accelerating to the speed of light and entering a black hole is the same thing, right?

Harald Fox
It depends what you mean with "the same thing". There is certainly a difference between sitting on a rocket and being accelerated slowly and falling into a black hole. For once, if you get past the event horizon you won't be able to get out again. On a different level however it doesn't matter what exactly provides the acceleration, what happens to time and time dilation is the same.

Student
At present, what do scientists believe that is contributing to the expansion of the Universe?

Harald Fox
It turns out that 75% of the energy in the universe comes from dark energy. This dark energy is equivalent to the cosmological constant that Einstein introduced into his General Theory of Relativity. This cosmological constant has exactly that effect: fueling the expansion of the universe.

Brutis
What lies beyond the quark?

Greg Davis
Do you mean the next frontier of discovery after quarks? Some would say the Higgs boson. Other than that, I don't know, but we are looking. Maybe the quarks themselves are made of smaller particles. We are looking for that here.

skiracer
hi, can you tell me what string theory is?

Greg Davis
Sure. String theory is a theory that says that all of the fundamental particles of the universe are really tiny loops of string. The theory also says that the diameter of this string is 10-35 meters, much smaller than we can see even here at Fermilab. It probably won't be confirmed or disproven for a very long time - if ever.

Student
What is Supersymmetry?

Harald Fox
Supersymmetry ads another symmetry to nature. The effect is that to every particle that we know, there should be a supersymmetric partner of that particle that differs to the original one by spin 1/2.

skiracer
What does the standard model say then?

Greg Davis
String theory is not part of the Standard Model at all, though it is consistent with it.

Brutis
How about string theory?

Harald Fox
That's an option, too. Many theorists are working on string theory and it has many interesting and compelling aspects. One of which is that it provides a natural framework to combine Gravity and the other forces that we know.

BentArm
What does "spin 1/2" mean?

Greg Davis
A spin 1/2 particle has a specific amount of total angular momentum equal to 1/2(1 + 1/2) = 3/4 times hbar. hbar is a fundamental constant of nature. If you measure the direction of the spin of such a particle, there are only two possible answers. A spin 1 particle could have three answers, and as the spin goes up the number of possible measurements goes up. A particle with a great deal of angular momentum can have essentially any direction, like a real macroscopic top.

skiracer
Are you doing any experiments to prove string theory?

Harald Fox
We look for it in the experiments we do. Some versions of string theory predict the existence of extra dimensions. These extra dimensions may be discovered through the decay of particles and we're looking for those. So far we couldn't find any hint though.

skiracer
Yes, I know that but what is standard model about???

Greg Davis
The standard model is the theory of all particle physics we understand today. It tells us there are six types of quarks, six types of lepton, and explains the three forces that interact with them, the strong force, the weak force, and the electromagnetic force. The fourth force in nature, gravity, is still a mystery on this scale.

Charlie
When a body accelerates its mass increases. The heavier the body becomes, the more curved the spacetime around it gets. At the speed of light, the mass of a body would be infinite, and so will the spacetime curvature near the body, right?

Harald Fox
Yes, probably. But this is not an experiment you can do. As you state above, the object becomes heavier and heavier, so instead of putting energy into speeding the object up you put energy into making it heavier and heavier. So your object will never reach the speed of light.

sci123
If extra dimensions exist, what do they look like?

Greg Davis
If extra dimensions exist, their most remarkable quality is surely that they aren't obvious, like the four we already know about. Theorists suggest that we can't see them because they are "curled up" on themselves into a tiny tube. How big is very much an open question. Why this happened is also a mystery.

skiracer
Are you doing anything to prove string theory???

Greg Davis
Not directly, our measurements are looked at by theorists who use them to refine their theories. Also, when they make predictions about things we could see, we look for them. We don't have any signals yet though.

skiracer
Who were the main contributrers to string theory?

Greg Davis
There have been many physicists who have worked on string theory. Perhaps the most famous is Ed Witten from Princeton University. Fermilab also has a theorist name Joe Lykken who has worked on string theory and was featured in NOVA's presentation, "The Elegant Universe."

skiracer
I have learned a lot about the standard model but still don't understand what it is.....help?

Harald Fox
It's the theory of the particles and their interactions. It was developed over the last decades (and probably still is). There are 3 forces within this theory: 1) the strong force, responsible for holding the nucleus in the atom together 2) the weak force, causing the beta-decay and 3) the electromagnetic force. Those forces are mediated by bosons. Then there are the other particles of the standard models that interact via those fundamental forces: neutrinos via the weak force, electrons (and its siblings) via the weak and electromagnetic force, and quarks, which interact via all 3 forces.

skiracer
What is the DZero experiment???

Greg Davis
DZero is the experiment that both Harald and I work on. It is a large detector that looks at the particles emmitted from the high energy collisions the Tevatron provides. We have over 500 collaborators from around the world who helped build it, run it, and analyze the data. Our webpage is at http://www-d0.fnal.gov.

sci123
What are quarks and lepton?

Greg Davis
Quarks and leptons are some of the fundamental particles in the Standard Model. In both types, there are six "flavors" that come in three pairs called doublets. All leptons and quarks feel the weak force, but only quarks feel the strong force. The six leptons are the electron, muon, and tau, and each has a neutrino partner. The six quarks are up & down, charm & strange, and top & bottom.

Student
Is there such a phenomenon known as "proton decay"? If so, what is/are the products of proton decay?

Harald Fox
There were whole experiments dedicated to the discovery of the proton decay. So far it hasn't been found. There was a GUT (Grand Unified Theory) that predicted this decay. If we had found it, that theory would have been confirmed and we would know a lot more about the structure of the fundamental forces that we see. But, the proton lives longer than 1.6x1025 years and that theory was ruled out.

skiracer
Sounds awesome, can visitors come near the experiment??

Greg Davis
We have open houses approximately every month where something is open, occasionally they are experiments. If you are a student, your teacher could arrange a tour for your class. We do this sort of thing all the time.

skiracer
When will the transcript of this be available on the web

Moderator
Skiracer, the transcript will be up within the next couple of weeks. Look for it on the Virtual Ask-a-Scientist webpage: http://www.fnal.gov/pub/inquiring/virtual/index.html

skiracer
What do you consider yourselves??? Scientists Experimentalists? Theorists?/

Greg Davis
Harald and I are both experimental physicists. This is one type of scientist, and most of the scientists at Fermilab are like us. The lab also does have some theorists who do not work on experiments, but rather spend there time thinking about theories and making calculations.

skiracer
What was or is your most recent discovery???

Harald Fox
I think a very important recent result was the WMAP data. WMAP is a satellite that measures tiny fluctuations in the temperature of the Cosmic Microwave background. The result of that measurement is that we know only 4% of what makes up the energy in the cosmos. The rest is Cold Dark Matter and Dark Energy. It also tells us that the Universe is flat to an amazing degree. This data gives confirms predictions by Inflation, a rapid expansion of the universe shortly after the big bang. On the particle physics side it's probably the discovery that neutrinos can oscillate and therefore must have mass.

Charlie
Isn't there a possibility that the effect of gravitational collapse whould occur as a moving body accelerates to the speed of light? If this happened, then we whouldn't have to put more energy, because the body whould collapse under its own weight and it whould form a black hole. What do you think about that?

Greg Davis
A single body that is not a black hole can not become one just through speed. The reason for this is actually very cool. Imagine you are sitting on the particle. The particle thinks it is sitting still and the rest of the universe is wizzing by. There is no reason for IT to become a black hole. On the other hand, some people theorize that if two particles hit each other very hard, they could become a black hole. We don't have any evidence of that yet, but it could be that we just haven't created high energy enough collisions yet. Don't worry though, such a black hole would evaporate extremely quickly.

skiracer
I am a student, but I could not probably visit with my class even though my teacher would love that because we are located in Colorado!!!!! Wish I could though!

Greg Davis
If you do find yourself in Chicagoland, contact the Education Office, we'd be happy to show you around. There have been school groups that have come from very far away. Ask you teacher, you might be surprised by his or her answer.

skiracer
What are your opinions on string theory???

Greg Davis
I don't think that it will be confirmed or disproven in my lifetime, the strings are just far too small. It would be cool to be proven wrong on that prediction, but I am not optimistic.

sci123
Is it possible to exceed the speed of light? Have you done any experiments on it?

Harald Fox
Theory of Relativity forbids to cross the speed of light boundary. You can never accelerate a body to the speed of light or beyond. In the accelerator we're using that's our daily bread and butter. We're accelerating protons and antiprotons to an energy 2000 times their rest mass. But never beyond the speed of light, sorry.

Jon
Hello I am a high school student from Troy, MI interested in particle physics and in working at a lab. What kind of education would I need?

Greg Davis
If you want my job, then you need to go to college and study physics, probably as your major. Then you go to graduate school at a program that will send you to Fermilab. I am a Ph.D. student now.

Jon
Would I need a graduate degree to work though?

Greg Davis
I got my M.A. while I was here and will be finishing my Ph.D. in January. It has taken many years, I graduated from college in 1997 and then went directly to the University of Rochester, which now employs me.

sci123
Where is FermiLab located?

Harald Fox
It's in Batavia, Illinois. It's about an hour west of Chicago.

sci123
How do auroras form?

Greg Davis
Auroras are cool, and I've only seen photos, never the real thing. What happens is that particles travel along the earth's magnetic field. That field is strongest near the poles, and that is why there are only enough such particles to be seen there.

skiracer
What is your opinion on the standard model

Greg Davis
The Standard Model is a great success. It has made some incredible predictions that have all worked out so far. It has been changed some over the years to accomodate new data, but not much. Unfortunately, it does not predict what happens in some realms, like that of gravity. It is probably just an excellent approximation in our realm of some greater theory of everything.

sci123
When is the best time to see the meteor shower tonight?

Greg Davis
I didn't know there was one tonight. I would check out "Sky and Telescope" magazine online to see.

Charlie
What tells us that the Higgs field isn't just another ''ether'' for modern physics?

Harald Fox
In the end nothing, but there are some differences. I think of the ether more as a philosophical construct to be able to understand the universe. I haven't seen any theory that really needed the ether. The Standard model however does. Without the Higgs particle many of the calculations we are doing are simply not possible. You need the Higgs to cancel out other terms in our equations. It also provides an understanding of the symmetry breaking of the electromagnetic and weak forces. Thus it's an integral part of our standard model, in terms of understanding and in terms of calculation. But in the end it's "just" part of a theory that can be proofed wrong by the experiments. If it doesn't exist though we have to look for something else.

Jon
Where does the new meson discovered fit in the particle scheme? It's a pretty big deal as I see it.

Greg Davis
I don't know too much about this, but I have seen some stuff. It is very cool to see a new particle, but I am not shocked because we really don't know how to make calculations about the strong force very well. It is probably a state that we just didn't think of before.

Jon
Thank goodness finally particle physicists have gotten together to make Interactions.org as a site to tie together all the info on this subject floating around on the web. I love the updates. Thank you also for taking the time to answer mine and the others questions. They help a lot.

Greg Davis
I am glad you like it!

Student
What is the maximum energy the FermiLab can accelerate particles to in giga-electron volts?

Harald Fox
The Tevatron can accelerate protons and anti-protons to 1960 GeV! It's at the moment the accelerator with the highest energy in the world. In a few years LHC at CERN in Geneva, Switzerland will be the accelerator with the highest energy.

skiracer
How is string theory providing a bridge between quantum theory and theory of relativity?

Greg Davis
String theorists claim that it is exactly that bridge. It might be. It does seem to explain how all four forces: the strong, the weak, the electromagnetic, and the gravitational can coexist, but it is just impossible to verify if it is true, at least so far.

Guest
Where is the Sky and Telescpe magazine?

Greg Davis
I don't remember the address, but if you put "Sky and Telescope" into google.com, I am sure you will find it.

Jon
What do you mean "we really don't know how to make strong force calculations very well"?

Greg Davis
Good question. We have a theory of the strong force. It is a very complicated differential equation. We can find good approximate solutions at some energies, but not all. If we understood the strong force completely, we would be able to do a calcuation showing why the proton has the mass it does, like we can calculate the properties of a Hydrogen atom. Right now, we can not do that. So new states, like the new meson from Belle, can still happen.

Jon
How do WIMP's fit into the standard model and are there any results from the CDMS experiment?

Harald Fox
They don't really fit into the "Standard Model" as we know it, but that might just mean that we don't know everything yet. In fact 25% of the Universe is made up of Cold Dark Matter and we don't know what it is! We have a few ideas though. One of them is Supersymmetry. Supersymmetry predicts a lot of new particles and one or more of them could make up this Cold Dark Matter. This would be an extension of the Standard Model though. The CDMS experiment contributes to these searches. Although they didn't find any WIMP they certainly have results. Check out http://cdms.berkeley.edu for example.

Charlie
What is the most important thing you have learned in your career as experimental physicists?

Greg Davis
What a great question. I have learned a great deal about the universe itself and how it works, and that is the thrust of our research. Of course, I have also learned about electronics, computers, and working with other people. When you work on something so big and complicated you also learn a lot about yourself. I have been very surprised at times to see both what I am and am not capable of personally. Maybe that is the most important thing.

Charlie
Are positrons electrons travelling backwards in time, and if yes, can matter turn into antimatter by moving faster than the speed of light?

Harald Fox
The Theory of Relativity forbids that something can be accelerated to or beyond the speed of light. So you cannot turn an electron into a positron that way.

Jon
What do you scientists answering questions do at the lab (theoretical, experimental etc.)?

Greg Davis
Harald and I are both experimenters on the DZero experiment. We spend some of our time running and improving the detector and some of our time pouring through the data trying to understand what it is telling us. Recently, I have also spent a lot of my time writing my doctoral thesis. We also spend some time doing outreach to the public, like this.

Student
Are there any other stable baryons apart from protons and neutrons?

Greg Davis
Baryons are particles made from three quarks. The only stable baryon is the proton, even free neutrons decay eventually, though it takes a long time before they do. In nuclei, the neutron is effected by the environment and can sometimes become stable. No other baryon is stable at all.

Charlie
What is the bridge that connects our spacetime with the extra dimensions?

Harald Fox
Well, so far we don't know whether there are extra dimensions. There are theories though that work in as many as 11 dimensions. One possibility is that we are confined to our usual 3+1 dimensions, but that gravity can see all dimensions that exist. This kind of theory would predict that there is a small deviation of Newton's law at small distances. Once way to discover extra dimensions is to search for that!

Jon
Are tachyons still believed to exist or are they just hypothetical and what exactly are they?

Greg Davis
Tachyons are very cool and might exist. However, Special Relativity tells us that we can not interact with them. If we cannot interact with them, we cannot detect their presence.

Guest
Thank you soooo much for all the info...I wish that you did this more often!!

Greg Davis
Skiracer, we try to do this monthly, but the schedule is not fixed. Each time, you get different people to chat with.

Student
Why is parity not conserved in weak-interaction beta-decay?

Harald Fox
That's a feature of the weak interaction. On the technical side: the weak interaction could have been a scalar (S), a vector (V), and axial-vector (A) or a tensor (T) coupling. In the end it is an experimental measurement that nature has picked an interaction that looks like (V-A). But there is no reason for it as far as we know. It's just a fact of life.

Student
Is "mirror asymmetry" exhibited in subatomic particles?

Harald Fox
The mirror asymmetry is exactly the parity violation you asked about earlier. So yes, parity or mirror symmetry is violated by the weak interaction, for example in the beta decay of the element Co60. This is by the way one of the famous experiments that established parity non-conservation.

Student
How do particles interact via the weak force?

Greg Davis
The weak force is mediated by the Z and W bosons. The Z boson has no charge and the W has a charge of plus or minus the electron charge. They are very massive, and that is why the force is "weak." Particles need to be very close to exchange a massive particle like these.

Student
Is there such a particle known as the "upsilon"?

Harald Fox
Yes, an Upsilon is a Meson that consists of a b-quark and an anti-b-quark. Its existence is exploited at SLAC where the Upsilon resonance is used to create b-mesons.

Charlie
What is space and time?

Greg Davis
Space and time are not really separate ideas, there is really just one thing: spacetime. Spacetime is the 3+1 dimensional "space" where we live. "Space" in quotes is a mathematical term, not a physical one. I say 3+1, because we have three spatial dimensions and one time. The reason it is one thing however, is because while everybody agrees that there are these 3+1 dimensions, we disagree on their measurement. This is the idea that time slows down when travelling close to the speed of light.

Charlie
What is the difference and the connection between a wave and a particle?

Greg Davis
All particles are waves. The wave nature tells the particle where to go, but it interacts either completely or not at all, like a particle. Big particles, like bowling balls or the moon also behave this way, but their wavelength is absolutely miniscule, so their wave nature is extremely surpressed.

Student
Do all particles that have mass oscillate?

Greg Davis
No, protons are massive, and they do not oscillate. The inverse however is true, only massive particles can oscillate. That is how we determine that neutrinos are massive - they do oscillate.

Student
Can the singularities of black holes be the "location" where Quantum mechanics unifies with Relativity?

Harald Fox
I'm not quite sure what you mean by a location of unification. If a quantum theory of gravitation exists then it exists and is applicable everywhere. It might not be the most convenient and most efficienct way to use it all the time, but in principle you could use it, say in the daily weather forecast. If that's really a fundamental theory it has to be valid everywhere. But you're right in the sense that in a black hole quantum effects in gravity become important. If we want to calculate what's happening very close to the center of a black hole then we need to use this kind of theory.

Student
Are all supersymmetric particles necessarily heavier than their particle counterparts?

Greg Davis
Yes, because they have not been seen yet. If, say the top quark's partner were lighter than the top quark, we would have seen it first.

Student
What does "oscillate" actually mean?

Greg Davis
Oscillate means switch back and forth. It seems that muon neutrinos oscillate to becoming electron neutrinos and tau neutrinos over time.

Jon
How would you go about detecting a graviton? Could it be done at Fermilab?

Greg Davis
This is not something we are looking into at Fermilab, as far as I know, but there are experiments elswhere. The LIGO experiment is looking for this by trying to see things change shape from gravitational waves. That would be many gravitons at once. You can learn more http://www.ligo.caltech.edu.

Jon
Do you do any experiments there with quantum entanglement?

Greg Davis
Not to my knowledge. However, I have friends who work on this kind of thing at the University of Rochester. Work on this is going on all over the world. It doesn't require a huge facility like Fermilab to do this work.

Student
Is there any direct/indirect evidence that the Universe's expansion is due to the presence of dark matter?

Harald Fox
I guess you mean dark energy? There is both in the universe: 25% dark matter and 70% dark energy, at least that's our best estimate right now. Ordinary matter would cause the expansion to slow down. Dark matter in that respect is just like ordinary matter. You actually can detect its presence also in our galaxy when you observe the movement of the stars. What we see globally in the universe is that the expansion is actually accelerating. And the only theory we have for that is dark energy, or the cosmological constant.

Jon
I seem to have heard something about a particle made of 5 quarks; do you know anything about this and could it be possible to have an infinite number of particles with different combinations of 3, 4, 5, 6 etc. quarks or leptons in them?

Greg Davis
The way we understand the strong force, the total number of quarks in a particle has to be either zero or a multiple of three. Most mesons (a month ago we would have said all mesons) have one quark and one antiquark, summing to zero. Baryons have three quarks. You could though have a baryon with four quarks and one anti-quark, summing to three. Leptons do not form composite particles like quarks do.

Student
Do all the states of the particle change after it has oscillated?

Greg Davis
If a particle starts out a muon neutrino and then becomes a tau neturino, it has changed completely from one to the other. Does that answer this question?

Jon
Why must the forces be unified into one, and how would one go about detecting that and why are theories failing to?

Harald Fox
They don't have to, but it would be nice if they would! I guess it's like electromagnetism. Originally those were 2 different forces until Maxwell came up with a combined theory - and that was very successful. Something similar happened with electromagnetism and the weak interaction. In fact there is a unified formalism to describe both forces. In the end it boils down to simplicity: it would be a beautiful theory if there was one that could explain all the forces. And so far this approach has been proven extremely successful. In fact in the end all forces can be traced back to symmetries. From our past experience there is no reason to believe that there couldn't be a global symmetry that governs all forces. But, it doesn't need to be that way.

Student
Well, thank you very much for your time today!

Greg Davis
Its always fun to write to interested people. Thank you all for these questions, some were very thought provoking.

Moderator
Thank you everybody for participating in tonight's Virtual Ask-a-Scientist. I hope to see you at the next chat session on December 18. Good night!

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