Severian

The actual measurement (from WMAP) is: [math] \frac{n_B - n_{\bar B}}{n_\gamma} = (6.1 \pm 0.3) \times 10^{-10}[/math] where [math]n_B, \, n_{\bar B}[/math] and [math]n_\gamma[/math] are the number of baryons, anti-baryons and photons respectively. The number of photons is just used for normalization - the important thing to notice is that the number of baryons minus anti-baryons is different from zero (more than can be explained from the small error). BTW, baryons are things like protons and neutrons.

No. Since all speeds are relative, your motion changes the speed of the cannonball you observe, as you say. Indeed, this is present in normal Newtonian mechanics too. The difference is how you compute the change from one observer to another. If the cannonball is doing 10,000fps (fast cannonball!) compared to you, and your friend is moving at 5,000fps relative to you in the same direction as the cannonball, Newtonian mechanics tells us that the cannonball will be doing 5,000fps relative to him. This is not true in relativistic mechanics since velocities don't add linearly. However, the momentum, defined as [math]p=\gamma mv[/math] with [math]\gamma=\frac{1}{\sqrt{1-v^2/c^2}}[/math], does add linearly, so you can still work it out. (In fact, it is because [math]\gamma \approx 1[/math] for slow objects that makes [math]p \propto v[/math] making it look like velocities add linearly in 'real life'.) No. there is no such thing as absolute speed. Everything is relative.

Tachyons aren't in condradiction with SR, but that is not the same as being predicted by SR. Scientists tend not to like tachyons, because if their mass squared is negative they contribute negatively to the energy of the universe. So the lowest energy state is therefore to have more (infinitely more!) of the tachyonic particles and the entire vacuum destablises. The fact that the universe exists is fairly good evidence for the non-existence of tachyons (there could be some mechanism preventing their creation, preventing the destabilisation, but it is not clear what that mechanism would be).

The speed of the object isn't an intrinsic property of the object. One can only have speeds relative to something else. So the ship has a 'speed relative to observer 1' and a 'speed relative to observer 2'. These are different quantities, so they don't have to be the same. That is why it is called 'relativity'. (Incidentally, the adding of velocities as you describe is not true in SR, but that is a different issue.)

I must admit, after reading this thread I nearly deleted this site from my bookmarks. Only Lucaspa's posts prevented me from doing so.

As I said, I have never seen it proven. Remember you can't use the renormalization group equations because they break down when the coupling becomes non-perturbative. Ironically you have to use a lattice, but I thought that had only been done for [math]\phi^4[/math] theory (Luescher?). As you yourself point out, QCD has no Landau pole but it is a gauge theory, so it is certainly not generic. Also note that QCD never reaches its infra-red pole due to hadronization. I suspect that QED would do something similar at very very high energies - that is non-perturbative interactions with the vacuum would turn the beta function around. (I don't see how this would work though since you don't have enough freedom in the theory to create bound states.) I understand your point, but I would not expect my final theory of everything to be divergent in the ultraviolet. I think that would be a sign that the theory is wrong. So I don't see any inconsistency in having an upper cut-off on the energy set by a lattice. Even if the Landau pole were present in the theory, the cut-off itself prevents it. Are you saying that a viable theory has to permit arbitrarily high energies? This is just an aesthetic argument. To my mind, string theory's big problem at the moment is that it is non-predictive, so it really doesn't get out of the starting gates as a desirable theory. Unlike some people, I am willing to give string theory a chance to actually make some quantitative (or even qualitative) prediction, but until it does, why should I even consider it? I think it was a big tactical mistake for certain string theorists to invoke the landscape and admit that string theory give you anything you want. I wouldn't say I know him personally. We have met and I have heard several of his talks. He recently gave a talk about his 'OSET' idea at CERN and insulted just about every experimentalist in the room - they weren't very happy afterwards. He comes over as very arrogant and doesn't pay very much attention to the literature. I think he is very good, and has some nice ideas, but he is no Witten (or Weinberg).

It is a rather bogus argument in my opinion. Firstly, I don't think the Landau pole in QED has ever been proven (though I could be wrong). Secondly, gravity looks nothing like QED so I see no reason why there would be a Landau pole in gravity. Even if there were, it's presence must be due to a poor description of the theory itself, not the approach taken (i.e. LQG). A Landau pole is intrinsically non-physical and is only tolerated in QED because we expect a UV completion. Don't believe the hype about NA-H, especially not from his grad students.

There is such a lot of crap in this thread, so lets try and clear things up a bit. Anti-matter is just like matter but with opposite quantum numbers (but the same mass and spin). It has positive energy. An example of anti-matter is the positron which is the anti-particle of the electron. When matter and its antimatter variant come into contact, they can annihilate to form photons (they do ths because the quantum numbers cancel, giving the same quantum numbers as the photon and it is energetically favourable to decay to a lighter particle). Exotic matter is any type of hypothesised matter which is not a part of the Standard Model. So antimatter partners of known fields (like the positron) are not exotic matter, neither is the Higgs boson. However, supersymmetric particles are exotic matter, although nowadays people don't really call them that since so many people expect supersymmetry to be discoverd soon. An axion wold be a good example of exotic matter. Notice that nothing in this definition of exotic matter implies that it will annihilate with ordinary matter. In fact, it is rather unlikely to do so since it would have to have exactly the opposite quantum numbers to some known matter particle.

Its a typo, obviously. Stop being such a wanker... By the way, it is fixed now.

Well, you could always sneak in. Nobody checks at the door. (Though there is a registration fee, so I am not encouraging this.)

The 2007 EPS conference on particle physics is currently taking place at Manchester, and I thought a few of you might be interested. The main website is: http://www.hep.man.ac.uk/HEP2007/ and the scientific program can be found at: http://agenda.hep.man.ac.uk/conferenceTimeTable.py?confId=70 Most of the talks are now online, so you can have a browse if you like. I found this talk quite interesting: http://agenda.hep.man.ac.uk/getFile.py/access?contribId=105&sessionId=3&resId=0&materialId=slides&confId=70

It's not a spheroid. It's a geoid. Minor point I know.

Superstrings look like wriggly eels (without the eyes of course). I though everyone knew that!

Unfortunately it doesn't work, since the Standard Model doesn't have enough CP violation to do this. Ho hum! Let's be honest, no-one has the foggiest what is going on. He may have been asking about what happened to all the 'universes' with different vacua, a la Linde and Susskind. If that were the case, then in their fantasy model, the other 'universes' are still there - they are just so far away that we don't see them (there is a tendancy for the local area to copy the same vacuum, so one would expect our local area to look the same). But it is not a billion different 'universes', it is 1015000!

I think you have a misconception about antimatter. A positron does not have negative energy - it has positive energy, just like an electron. In fact, it is convention which one is matter and which is antimatter. The fact that the 'cancel each other out' is just that they have opposite quantum numbers (eg charge, lepton number etc) so the resulting object must be neutral etc but will still have energy. In fact, when a positron and electron meet and annihilate, they produce light. Your statement "how do we know that the "anti-photon" isn't the same as the regular photon" is exactly correct. The photon is its own antiparticle.

Science can never answer the question 'why'. It just answers 'how'. We can only ever contruct theories that describe how the universe works, but to say 'why' it is like that is philosophy, not science. Classical gravity is very well understood in terms of General Relativity. If you don't agree with that then you are not understanding GR. Quantum gravity on the other hand, is not understood (yet).

The amount our PhD students learn in their first year is ten times more than everything they have learned in their entire undergraduate studies.

It'll all in in tears. Mind my words...

There has been a recent upsurge in the number of people studying 'string phenomenology' in the US. But all that goes to show is that the string theorists don't understand the word 'phenomenology'.

Nice tits

I hate these sort of puzzles. Any rule which correctly matches the presented numbers provide a valid answer, but there are always multiple rules which supply the same presented numbers but diverge once you get beyond them. But you are always required to get inside the twisted little mind of the guy who set the problem and present the answer that he thought of, even if another is more logical. For example, following Igosaur's lead, I could ask for the next number in the series: 1 11 21 1211 111221 111222211 ?

No - it is definition. Simultaneous events are ones which lie on the same light cone, so all events in a photon's 'life' are simultaneous by definition, and therefore time is meaningless to a photon. You can define time differently if you like, but then you are being non-conventional...

Even if I wasn't paid at all, I would rather be a brain surgeon than a window washer.

There is a problem with each of them, unfortunately. The problem with the W and Z bosons is that they are very heavy. It takes a lot of energy to make them and then they decay very fast. This is why the weak interaction is so short range: the W and Z bosons which 'mediate' the force can't get very far from the source before they decay. The problem with the strong interaction is that it is too strong. If you take two colored objects lift quarks and move them apart, it becomes increasingly difficult with greater distance, just like having an elastic string between them. Eventually the string breaks, or more correctly you put enough energy into the system to make a quark-antiquark pair out of the vacuum. They then move towards your original color charges, making them color neutral.

Having lived in quite a few countries with quite a few different systems, I am of the opinion that a 'free' universal healthcare service (like the UK's NHS) is a bad idea. It breeds inefficiency and ends up providing a worse service for everyone. The only bonus it has is making sure that everyone has medical care should they need it. But this can be done in better ways. In my opinion, the best system is to have a completely privatised health care system (hospitals, general doctors, pharmacies etc) but require everyone by law to have some form of health insurance. It may seem draconian to force people to have health insurance, but what is the alternative? You would have to let people die who didn't have insurance. The current system in the US of allowing people to opt out of insurance but then still patching them up after their car-crash is a bit counterproductive because you reinforce their belief that they don't really need insurance. Since this option is probably not going to be tolerated by the public, health insurance needs to be mandatory. In order to keep the price of health insurance low, the state should provide a subsidised health insurance. This should be a very basic service (basically emergency medical care and life threatening conditions) and would place a limit on the market preventing insurance companies from taking people hostage. It doesn't have to be a big expense for the state, since it can adopt the policy of charging enough to just about break even.