Yes and no. The Linear Collider doesn't depend on the discovery of the Higgs per se, but it does become more compelling if the LHC (or Fermilab) discovers _something_. The most likely scenario is that the LHC (which comes online in 2007 or so) at CERN will discover some new things - supersymmetric particles, the Higgs, the physics that gives us neutrino masses, etc. The Linear Collider would then be used to study what's been discovered. If the LHC doesn't see anything interesting (which most physicists think is unlikely, because of various arguments, but it's possible), then the Linear Collider will be a lot less useful. But there are a LOT of different ideas for what the LHC could discover - it doesn't all hinge on testing one particular model.
From the physicists' point of view, though, you don't want to wait that long. Say the LHC starts in 2007 (though such projects are often delayed) and discovers something by 2009. Then you start a proposal for the Linear Collider, which you finalize by 2012. Then you build it, and it's working in 2020. That's a LONG wait! These projects take so long that physicists want to get the ball rolling and construction started ASAP.
Most of the mass in the universe is indeed "missing". In the past 10 years, however, we have learned quite a bit about its properties - it so far seems like real stuff, not just a mathematical artifact. It's still very possible, however, that there is no missing mass and that we need to change our ideas about gravity.
No, the effects of gravity don't move instantaneously. In general relativity, its effects propagate at the speed of light. Therefore, if the sun was moved right now, the earth's orbit wouldn't be altered for 8 minutes or so. There's so far no connection known between this and quantum entanglement.
One thing people forget about the Higgs boson is that it doesn't necessarily need to be there, at least not in its usually-understood form. In the electroweak theory, there is a symmetry of nature which makes the electromagnetic and weak forces look the same at high energies (i.e. in the early universe when things were very hot). At low energies, this symmetry is "broken", and so the two forces look different. Its sort of like a ball perched at the top of a perfectly symmetrical hill - when the ball stays on top the situation has a lot of symmetry, but the symmetry is gone when the ball randomly chooses one side to roll down. The predictions of this theory have been stunningly successful (it led to a Nobel Prize in the 1970s). In this theory, the Higgs boson and its associated interactions control the way in which this symmetry is broken - it controls the shape of the "hill".
However, all the theory really says is that this symmetry exists and that something breaks it - there's no guarantee that it's a single new particle (Higgs boson) that does the job. There may be several Higgs particles, or even some entirely new physics that breaks this symmetry, and all the experimentally-verified parts still work. The usual idea of a single Higgs boson is only the simplest case.
Even though we don't know what form this new physics will take, there are pretty good (though far from airtight) arguments that say that whatever it is has to happen at energies below about 1 TeV. The idea is that if the "natural" energy of electroweak physics is a billion TeV, say, then it would be very strange for the energy scale of the weak force to be at 0.1 TeV (which it is) - a bunch of really big numbers need to almost cancel, but not quite, in order to get that kind of discrepancy. Physicists are thus fairly convinced that either (1) there is a Higgs boson in this energy range, and so the LHC will find it, or (2) something else even more interesting happens in this energy range, and so the LHC will find that. This is, of course, not a sure thing by any means.
There is a sense in which statements like Hawking's are less scientifically satisfying than predictions about the properties of materials or even predictions about what will be seen at particle accelerators. In physics we're always working in mathematical reverse - we look at the complicated results of a zillion experiments and try to figure out the fundamental principles that let us explain them all. Theoreticians (like Hawking) also try to work forward and see what they can derive from these principles. It's always possible that these derivations go a little too far and can yield wrong results. If a theorist claims they can tell you what's happening inside a black hole, take it with a grain of salt - it might be right, but so far we can't be sure.
There's still a big difference between that and pink elephants. Quantum field theory and relativity have been tested ridiculously strictly (especially the former) over a very wide range of scales and energies. Even though physicists believe they aren't the final answer, they give the right answer so often that one starts to believe that they contain insight into the truth. If those two theories start to tell you something, you think about it seriously, even if you can't yet see how to test it. Even if it's wrong, the reasoning involved might lead you in new directions toward new fundamental principles. I can't say the same for the previous poster's offhand remarks about the distribution of chromatically diverse pachyderms.
Astronomers have a whole range of different ways to measure distances, each of which works in a different regime. They form a "cosmological distance ladder" - you attempt to calibrate each new method during its overlap region with the previous method.
Parallax is the method for the very shortest distances (nearby stars).
For intermediate distances (distant stars in our own galaxy, relatively nearby galaxies), most of the methods come down to finding some sort of "standard candle" - something that you know the intrinsic brightness of, so you can use its apparent brightness and the inverse square law to calculate its distance. Astronomers tend to use particular types of variable stars (stars with a well-defined cycle of brightness changes) for this purpose. For galaxies, you can sometimes use averaged properties of all the stars to estimate the distance.
For cosmological distances (very distant galaxies) the most common trick is to use redshift. Because of the universe's expansion, an object twice as far away is receding from us twice as fast, and so its light is Doppler-shifted twice as much. Ideally, you look for known features of the object's spectrum and see what wavelength they have ended up at. This is what people are talking about when they measure the distance to Hubble's latest find.
There is also a complementary method that uses standard candles at cosmological distances. In this case, you use Type Ia supernovae, a particular type of exploding star that looks pretty much the same every time. They're bright enough to be seen very far away, and again you can get the distance using the inverse square law (modified by general relativity). It's the difference between this method and the redshift method that provides the strongest evidence for dark energy - it shows us that the universe is expanding faster than we expect, and that this expansion is accelerating.
As far as I know, anyone who talks about tachyons as physical particles which we might use to construct warp drives or build a better mousetrap, is venturing into crackpot domain. The word does have a useful meaning in particle theory, which is indicated by the last paragraph of the entry. I'll give it a go, but this may not be helpful - it's unfortunately rather technical and abstract.
Imagine you're trying to see how some particle (field) behaves. You can sum up a lot of the field's properties by a potential energy function. This can be a crazy function with lots of peaks and valleys in it, and what it tells you is how much energy it costs for the field to be in a given state. Usually, the field chooses to sit in the minimum energy state possible - the "ground state", the deepest of the valleys. If you "kick" the field with some kind of interaction, it will go into oscillations rolling around the bottom of the valley. These excitations are what we call particles. (Sorry, I said it was technical and abstract).
A tachyon occurs when you made a mistake of sorts in your work - you picked the ground state to be at a peak rather than a valley. So the field value is such that you are perched atop one of these peaks. It turns out this would seem to correspond to a bizzare particle called a tachyon - a particle for which the square of its mass is negative (since the potential function is curving down instead of up). This isn't a real particle, though - if you "kick" the field when it's in that state, it won't oscillate normally to give particle states - it will roll off the peak and into a valley. This often happens when you spontaneously break a symmetry of your theory. Imagine your potential function looked like the letter "W". You might choose your ground state to be the one with left/right symmetry, but then you'd be on the peak of the W - you'd eventually roll off to the left or right and break the symmetry.
The take-home message is that the tachyon state isn't a real particle, it's an unstable situation that is an indication that you picked the wrong ground state. I think that in the early days of particle physics people didn't understand this kind of thing so well and thought tachyon particles might actually exist.
Sorry if I can't figure out how to make that much clearer.
The usual assumption is that WIMPs interact very weakly among themselves, as well as with ordinary matter. We expect them to remain as "smeared out" clouds, not as planet-scale objects. If WIMPs collapsed and clumped the way ordinary matter does they actually wouldn't be able to explain our observations - galaxy rotation curves ("watching star and galaxy orbits") indicate that the dark matter cloud is much bigger and smoother than the visible galaxy.
That being said, many models yield WIMPs which interact weakly with each other and ordinary matter (hence the hope of detecting them at all). We also expect (though the reason for this is more theoretical) that the universe may contain approximately equal amounts of WIMPs and anti-WIMPs. They wouldn't annihilate much because of their weak interactions, but in places where WIMP density is unusually high (the galactic center, WIMPs captured in the sun's core, etc.) you might see a gamma ray signal from WIMP annihilation. Gamma ray astronomers are looking for this sort of indirect evidence, and some even claim to see a signal.
I apologize, the last statement was arrogant and wasn't needed. I was reacting to the "if I don't understand it then those fancy scientists must be wrong" card that I hear played far too often, which often comes from a different sort of arrogance.
My end point was that I don't know of other explanations that are just as plausible, and that there actually is a great deal of evidence. The exact identity of dark matter is, of course, still a mystery, and it's even possible that this whole concept will be replaced by something much more interesting.
The thing that makes the dark matter explanation compelling is that it makes so many different observations work. We don't have to fine tune things so much - it all fits together. Here are some examples.
1. Galaxy rotation curves - you can watch the orbits of stars in a galaxy to determine the distribution of matter in the galaxy. This shows that there is a lot more matter than can be accounted for by the stars and that it is distributed differently.
2. Gravitational lensing - you can see how light is bent by distant galaxies to map out their matter distributions. Again, there's a lot more matter than the stars can account for, distributed differently.
3. The cosmic microwave background - this one is complicated, but the idea is that you look at the "afterglow" of the big bang, released when the universe was as dense and hot as the surface of a star. We understand the physics of matter at these temperatures very well, and by studying the signatures of vibrations in this hot plasma, we can measure the properties of the early universe. We can see from this that the universe contains a lot of matter, and that the large majority of this matter is not composed of ordinary atoms (hard to explain, but fairly rock solid).
4. Light elements - Most of the universe's helium, deuterium, lithium and beryllium were created in the early universe, not in stars (the conditions aren't right). Again, the physics is very well-understood, nothing fancy. By studying the relative ratios of these elements, we can figure out the properties of the plasma in which they were formed (a bit hotter and you get less deuterium, the temperature falls too quick and you get less helium, stuff like that). Again, the universe has a lot of matter, and most of it isn't made of atoms.
5. Structure formation - if you work things out on supercomputers, you find that (if the universe containst only ordinary matter) the universe hasn't been around long enough to form the galaxies and galaxy superclusters that we see. Adding dark matter to the mix makes galaxies form faster - just enough faster!
And the beautiful thing is that all of these different arguments give essentially the same answer for the amount of dark matter and its basic behavior. You can tweak your theories to explain some of these observations, but no one has been able to explain them all - except with dark matter, the SIMPLEST explanation!!
Before you say something is "clearly inferior intellectual flotsam", learn what you're talking about...
A particle is only detectable if it interacts with your detector - it doesn't matter very much if it's heavy or light. Matter is almost entirely empty space (think about the space inside an atom between nucleus and electron), and so a particle should just pass through atomic matter unless it "reaches out and grabs" the electrons or nucleus. Protons, electrons, and most ordinary particles do just this - they interact strongly with matter, either via electric charge or the strong nuclear force. Dark matter particles are expected to be like neutrinos, only heavier - they interact so weakly that billions can pass through your body every second and never interact.
It's true we should consider the possibility that our model of gravity is wrong, and some physicists are working on just this idea.
The thing to remember is that there isn't just one observation that general relativity and dark matter are meant to explain - there are an enormous number of different kinds of measurements, ranging from star orbits to gravitational lensing to the abundances of light elements in the universe. It's actually very difficult to tweak (or even completely rewrite) our gravitational theory in such a way that it does away with dark matter and yet makes all the observations work so precisely. It might be true that our model of gravity is wrong, but dark matter is actually the SIMPLEST explanation we know of for the amazing stuff we see in the universe, not some kind of weird idea that's getting ruled out.
Umm... no one HAS ever observed anything travelling faster than light. People have built particle accelerators that try their darndest to make things go as fast as possible, and they only hit 0.9999.... times the speed of light. That's a triumph of relativity, not a failure. And all the mass dilation effects, etc. all come out exactly as predicted...
Re:Scientists think Einstein was wrong?
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Testing Relativity
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· Score: 1
The standard model doesn't give any real _wrong_ answers that I know of. There is the nasty detail that most field theory calculations give infinity if you do them naively, but there are well-defined ways to deal with those infinities and calculate finite answers, which are almost invariably correct. The only possible exception that springs to mind is the recent Brookhaven result about the muon's magnetic moment, but that's still being verified.
I would say that the problems come in the questions that the standard model can't answer - things that aren't within its scope. The standard model can't tell you the mass of the electron or the behavior of gravity - it's not that it gives the wrong answer, it's just that these are things you have to put in by hand, they aren't things the model is able to explain. Assumably we will someday be able to do experiments which are accurate enough that the standard model will give the wrong answer, just like it took a long time to construct an experiment for which classical mechanics gave the wrong answer.
It's worth noting that this experiment is fairly unlikely to give us any sort of answer about string theory. Physicists don't really understand string theory enough to determine whether it predicts any sort of signal that could be detected in this way - some theorists think it might, others disagree. It 's pretty likely that this experiment won't see anything new at all, in fact, but it's still important. If it sees nothing, we may be able to rule out some theories (though maybe not, since theorists are clever), and if it does we'll have discovered something truly remarkable. Science reporters seem to like to say that everything in physics is all about testing string theory, but there's more to it than that. In 10 years we may say string theory was crazy, or that it's right but has nothing to do with this sort of experiment. The point is to learn something about the universe, to see what rules it follows on different scales. We'll never know until we try it!
Re:Scientists think Einstein was wrong?
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Testing Relativity
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· Score: 4, Informative
It's not so much that Einstein's relativity is wrong so much that it's incomplete. General relativity (and special relativity) have passed with flying colors every test we've ever put them to. Quantum field theory (the framework of particle physics) has done at least as well (in fact, it predicts some numbers in nature to more than 10 decimal places - far better than general relativity!). These theories are GOOD - they give the right answers.
The problem is that both are incomplete in some way we don't quite understand. There are fundamental problems with making a quantum field theory of gravity - the two frameworks are very different, and they don't play well together. I wouldn't say that either is "wrong", they're just both incomplete. Both theories are probably nearly-perfect approximations to some sort of underlying framework (for example, string theory).
Since neither theory can be the whole story, we expect that when we impose difficult enough tests on either one, they will begin to break down slightly - the world won't quite do what the theory seems to say. This is an excellent way to look for clues as to how these two frameworks fit together. You can look at this as an extension to relativity or a replacement for it.
My random theory is that the reason that the U.S. gets a lot of crackpots has a bit to do with our history. We're taught from elementary school on up that the U.S. was founded on the democratic notion that the "common man" is equal to (or better than) whoever is in power at the time. This populism is great for a lot of reasons, but it also means its hardly surprising Americans don't trust authority figures. Many people feel that an ordinary person with common sense could walk right in and show the snotty types who think they know everything that they're doing things all wrong. So we get people who think that evolution contradicts the "common sense" of the Bible, quantum mechanics contradicts classical common sense, etc. and that whatever weird ideas they have are better. Some people think that, since they're as good as anyone else, if they don't understand something then it must be wrong.
I second that observation - I'm one of the only physicists on my experiment who doesn't use a Mac laptop! OS X has a lot of appeal in many parts of the science community - it allows a user the ability to transparently use a lot of unix/linux functionality (ssh, xwindows, etc) to deal with workstations and data servers and yet gives you a fun, slick user interface when you want it. Not to mention that Mac laptops, while somewhat delicate, are very nice.
The solution to the problem you mention first (how come the light hasn't already passed us) is that the universe is bigger than its current "horizon size" (the distance light could have traveled since the big bang). We can't see anything beyond the horizon, but that doesn't mean it isn't there. The light that our immediate neighborhood emitted 13 billion years ago has long since passed us, but there are points 13 billion light years away whose light has just had time to reach us today.
The way that the universe ends up bigger than its horizon is explained by the theory of inflation. The idea is that the universe expanded faster than light (distances grew exponentially rapidly, in fact) for a tiny fraction of a second after the bang, expanding by a factor of 10^50 or so in 10^-30 seconds. Since the expansion was faster than light, some points ended up far enough away that their light hasn't yet had time to reach us. This is not as ridiculous and contrived an idea as it sounds - there's actually a number of good particle physics ideas that could make things like this happen, and it's the only known way to explain a lot of our observations of the universe (including the one we're talking about now). The idea is accepted in some form or another by essentially all cosmologists.
As another poster mentioned, there doesn't need to be an edge or a center - imagine you're an ant on the surface of an inflating balloon. It will feel like everything on the surface is rushing away from you uniformly, regardless of where you are on the surface.
The fact that galaxies get "slapped together so quickly" is actually a rather good piece of the evidence for the existence of dark matter. The amount of visible matter in an ordinary galaxy (or galaxy cluster - most of these simulations are actually done with clusters and not individual galaxies) would actually take quite a bit longer to form than what we observe. These objects form because the occasional bit of the gas in the universe is slightly more dense than the neighboring bits, and that clump will tend to attract other bits by gravity and grow. The growth rate gets faster as the clump gets bigger (and hence exerts a stronger gravitational pull). We can get an idea of the size of the original "clumps" in the gas by looking at the patters of hot and cold spots in the cosmic microwave background (the leftover "heat" of the early universe), and they're not big enough for galaxies and clusters to form so quickly.
Here's where dark matter comes in. If there's extra "stuff" in the universe that isn't visible, then galaxies are actually a lot heftier than they seem and are able to grow much faster. There's a lot more to it than that, but this is the basic idea.
As far as we understand it, there is no "edge" to the universe - at least not one we're expecting to ever be able to see. The universe as we know it has been around for about 13 billion years since the big bang. During that time, light has only been able to travel a certain distance - 13 billion light years (there are some technicalities with the fact that the universe is expanding as the light is traveling, but that's the gist). So we don't expect to ever be able to see farther than that distance, and most theories predict that the universe inflates (expands really fast) early in its life and so is actually much bigger than that distance. So if there is an edge, it's so far away light hasn't had the chance to get here from there.
However, we can't even see that far. Earlier in the universe's history, it was much hotter and denser. Until about 300,000 years after the big bang, it was so hot and dense that it was opaque to light - light from before that epoch isn't able to travel very far without scattering, and can't reach our eyes. We can, however, see the last light that was released from the hot, dense gas just as the universe became transparent - this is seen as the cosmic microwave background.
After that, the universe was very dark and homogenous - there were no stars or galaxies, and hence nothing for us to see! This period is called the "dark ages", for obvious reasons. After some hundreds of millions of years, gravity caused gas to clump together enough to produce the first stars and galaxies. These are the earliest things (other than the microwave background) that we could hope to study in a telescope picture. Some theories suggest that these might be weird objects - supermassive stars a hundred times bigger than our sun, bizzare protogalaxies, etc. - and they'll definitely teach us a lot about how galaxies form.
So it's not the "edge", but it's probably quite near the edge of what we'll ever see.
I agree, it's very possible that some basic notion of ours about gravity is wrong - dark energy is very possibly a manifestation of that.
This doesn't mean the stuff on the webpage you link to is any good. The main page contains such crap as an attempt to use "logic, mathematics, and geometry" to explain why the constitution isn't working, how propulsion systems for UFOs work, and so on.
This is yet another example of someone thinking they can provide a "simple" explanation for the scientific phenomenon-of-the-week without bothering to learn any real facts about what he's trying to explain. Such stuff almost invariably makes no physical predictions and gives you no way to calculate anything important - it's just pseudological bluster.
Science is hard, and it works a lot better than some armchair philosophers seem to think - if you want to make a contribution, learn something about it.
You're right, the natural step when we learn that the universe doesn't obey Newton's laws should be to try to modify Newton's laws, not to imagine that there is a magic 95% of the universe with funny unobserved properties.
The thing is that this isn't the only evidence for dark matter. There are a number of different lines of evidence which lead to the same conclusion - the orbital behaviors of galaxies and their clusters, the adundances of various light elements in the universe, the behavior of the cosmic microwave background, x-ray emission from clusters, etc. It turns out that no matter how hard we try, we can't modify Newton's laws to get the right answer to all of these. Gravitational lensing (the bending of light by the mass of distant galaxies and clusters) is really impressive in this regard - modifying Newton's laws (and general relativity) in the desired ways should have essentially no effect on it, and it definitely looks like there's dark matter (and even allows us to map its distribution). Dark matter really seems like the SIMPLEST answer, from the point of view of someone who knows the data!
Dark energy was the subject of the article, however, and that's quite a bit different. As of right now, I'd say that we DON'T have very convincing evidence that this isn't just a modification of general relativity. All of our particle physics-related ideas seem far too complicated.
Oh, and chaotic systems still obey the laws of classical physics - the systems are just so complicated that knowing how the individual atoms are behaving is not very helpful for predicting the behavior of the macroscopic system.
Dark energy certainly acts a bit like antigravity, but it's generally not believed to be quite that. We really have no clue of its exact nature, however - we just know vaguely what it does. The usual suggestion (which dates in some ways back to Einstein, though he never guessed at dark energy) is that it's a cosmological constant - an additional term in the equations of general relativity. Others suggest it's a new kind of particle field. Either way, it has negative pressure. The details of negative pressure are a little confusing, but the gist is that if dark energy is the dominant form of energy/matter in the universe, the universe will expand nearly exponentially rapidly. It's not really an antigravity force, but it is really strange.
The fact that the universe is accelerating is not the same as the "big rip". The accelerating universe, as we understand it now, sort of means that the space between everything and everything else is getting bigger all the time. However, in order to discover this (and the expansion of the universe in general), we have to look at very distant galaxies - we don't see our own galaxy flying apart, and some other galaxies bound together in our local galaxy cluster are orbiting or moving toward ours.
In general, objects that are in bound states - whether gravitational bound states (like solar systems and galaxies) or other bound states (atoms, etc.) will remain held together even as the distant galaxies which are not tightly bound to us zoom away. Our own situation on earth would be completely unaffected - you'd need a big telescope to even tell the difference.
The idea of the "Big Rip" is that this condition that "bound things stay bound" (the dominant energy condition) might be violated, that dark energy might be so extreme that not even bound objects could keep from eventually dissipating. That idea is HIGHLY theoretical - there's no particular evidence for it, and until recently most theorists thought it was ridiculous. But, of course, this is science - we have to think about even the weird possibilities.
As a previous poster said, a galaxy like ours takes a couple hundred million years to rotate, and formation times tend to be on that order, also.
The fact that this galaxy exists so early is, in some ways, evidence for the existence of Cold Dark Matter (CDM) - a population of heavy elementary particles that we think comprises much of the universe's "missing mass". The argument is that if CDM didn't exist, then galaxies (and more importantly, galaxy clusters) would take a very long time to form - the gas dynamics of the early universe tends to resist their collapse. CDM provides a way out of this - the dark matter isn't affected by any of that, and it can collapse more quickly to form big "seeds" for galaxies to form around once the gas cools down.
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Yes and no. The Linear Collider doesn't depend on the discovery of the Higgs per se, but it does become more compelling if the LHC (or Fermilab) discovers _something_. The most likely scenario is that the LHC (which comes online in 2007 or so) at CERN will discover some new things - supersymmetric particles, the Higgs, the physics that gives us neutrino masses, etc. The Linear Collider would then be used to study what's been discovered. If the LHC doesn't see anything interesting (which most physicists think is unlikely, because of various arguments, but it's possible), then the Linear Collider will be a lot less useful. But there are a LOT of different ideas for what the LHC could discover - it doesn't all hinge on testing one particular model.
From the physicists' point of view, though, you don't want to wait that long. Say the LHC starts in 2007 (though such projects are often delayed) and discovers something by 2009. Then you start a proposal for the Linear Collider, which you finalize by 2012. Then you build it, and it's working in 2020. That's a LONG wait! These projects take so long that physicists want to get the ball rolling and construction started ASAP.
Most of the mass in the universe is indeed "missing". In the past 10 years, however, we have learned quite a bit about its properties - it so far seems like real stuff, not just a mathematical artifact. It's still very possible, however, that there is no missing mass and that we need to change our ideas about gravity. No, the effects of gravity don't move instantaneously. In general relativity, its effects propagate at the speed of light. Therefore, if the sun was moved right now, the earth's orbit wouldn't be altered for 8 minutes or so. There's so far no connection known between this and quantum entanglement.
One thing people forget about the Higgs boson is that it doesn't necessarily need to be there, at least not in its usually-understood form. In the electroweak theory, there is a symmetry of nature which makes the electromagnetic and weak forces look the same at high energies (i.e. in the early universe when things were very hot). At low energies, this symmetry is "broken", and so the two forces look different. Its sort of like a ball perched at the top of a perfectly symmetrical hill - when the ball stays on top the situation has a lot of symmetry, but the symmetry is gone when the ball randomly chooses one side to roll down. The predictions of this theory have been stunningly successful (it led to a Nobel Prize in the 1970s). In this theory, the Higgs boson and its associated interactions control the way in which this symmetry is broken - it controls the shape of the "hill".
However, all the theory really says is that this symmetry exists and that something breaks it - there's no guarantee that it's a single new particle (Higgs boson) that does the job. There may be several Higgs particles, or even some entirely new physics that breaks this symmetry, and all the experimentally-verified parts still work. The usual idea of a single Higgs boson is only the simplest case.
Even though we don't know what form this new physics will take, there are pretty good (though far from airtight) arguments that say that whatever it is has to happen at energies below about 1 TeV. The idea is that if the "natural" energy of electroweak physics is a billion TeV, say, then it would be very strange for the energy scale of the weak force to be at 0.1 TeV (which it is) - a bunch of really big numbers need to almost cancel, but not quite, in order to get that kind of discrepancy. Physicists are thus fairly convinced that either (1) there is a Higgs boson in this energy range, and so the LHC will find it, or (2) something else even more interesting happens in this energy range, and so the LHC will find that. This is, of course, not a sure thing by any means.
There is a sense in which statements like Hawking's are less scientifically satisfying than predictions about the properties of materials or even predictions about what will be seen at particle accelerators. In physics we're always working in mathematical reverse - we look at the complicated results of a zillion experiments and try to figure out the fundamental principles that let us explain them all. Theoreticians (like Hawking) also try to work forward and see what they can derive from these principles. It's always possible that these derivations go a little too far and can yield wrong results. If a theorist claims they can tell you what's happening inside a black hole, take it with a grain of salt - it might be right, but so far we can't be sure.
There's still a big difference between that and pink elephants. Quantum field theory and relativity have been tested ridiculously strictly (especially the former) over a very wide range of scales and energies. Even though physicists believe they aren't the final answer, they give the right answer so often that one starts to believe that they contain insight into the truth. If those two theories start to tell you something, you think about it seriously, even if you can't yet see how to test it. Even if it's wrong, the reasoning involved might lead you in new directions toward new fundamental principles. I can't say the same for the previous poster's offhand remarks about the distribution of chromatically diverse pachyderms.
Astronomers have a whole range of different ways to measure distances, each of which works in a different regime. They form a "cosmological distance ladder" - you attempt to calibrate each new method during its overlap region with the previous method.
Parallax is the method for the very shortest distances (nearby stars).
For intermediate distances (distant stars in our own galaxy, relatively nearby galaxies), most of the methods come down to finding some sort of "standard candle" - something that you know the intrinsic brightness of, so you can use its apparent brightness and the inverse square law to calculate its distance. Astronomers tend to use particular types of variable stars (stars with a well-defined cycle of brightness changes) for this purpose. For galaxies, you can sometimes use averaged properties of all the stars to estimate the distance.
For cosmological distances (very distant galaxies) the most common trick is to use redshift. Because of the universe's expansion, an object twice as far away is receding from us twice as fast, and so its light is Doppler-shifted twice as much. Ideally, you look for known features of the object's spectrum and see what wavelength they have ended up at. This is what people are talking about when they measure the distance to Hubble's latest find.
There is also a complementary method that uses standard candles at cosmological distances. In this case, you use Type Ia supernovae, a particular type of exploding star that looks pretty much the same every time. They're bright enough to be seen very far away, and again you can get the distance using the inverse square law (modified by general relativity). It's the difference between this method and the redshift method that provides the strongest evidence for dark energy - it shows us that the universe is expanding faster than we expect, and that this expansion is accelerating.
As far as I know, anyone who talks about tachyons as physical particles which we might use to construct warp drives or build a better mousetrap, is venturing into crackpot domain. The word does have a useful meaning in particle theory, which is indicated by the last paragraph of the entry. I'll give it a go, but this may not be helpful - it's unfortunately rather technical and abstract. Imagine you're trying to see how some particle (field) behaves. You can sum up a lot of the field's properties by a potential energy function. This can be a crazy function with lots of peaks and valleys in it, and what it tells you is how much energy it costs for the field to be in a given state. Usually, the field chooses to sit in the minimum energy state possible - the "ground state", the deepest of the valleys. If you "kick" the field with some kind of interaction, it will go into oscillations rolling around the bottom of the valley. These excitations are what we call particles. (Sorry, I said it was technical and abstract). A tachyon occurs when you made a mistake of sorts in your work - you picked the ground state to be at a peak rather than a valley. So the field value is such that you are perched atop one of these peaks. It turns out this would seem to correspond to a bizzare particle called a tachyon - a particle for which the square of its mass is negative (since the potential function is curving down instead of up). This isn't a real particle, though - if you "kick" the field when it's in that state, it won't oscillate normally to give particle states - it will roll off the peak and into a valley. This often happens when you spontaneously break a symmetry of your theory. Imagine your potential function looked like the letter "W". You might choose your ground state to be the one with left/right symmetry, but then you'd be on the peak of the W - you'd eventually roll off to the left or right and break the symmetry. The take-home message is that the tachyon state isn't a real particle, it's an unstable situation that is an indication that you picked the wrong ground state. I think that in the early days of particle physics people didn't understand this kind of thing so well and thought tachyon particles might actually exist. Sorry if I can't figure out how to make that much clearer.
The usual assumption is that WIMPs interact very weakly among themselves, as well as with ordinary matter. We expect them to remain as "smeared out" clouds, not as planet-scale objects. If WIMPs collapsed and clumped the way ordinary matter does they actually wouldn't be able to explain our observations - galaxy rotation curves ("watching star and galaxy orbits") indicate that the dark matter cloud is much bigger and smoother than the visible galaxy. That being said, many models yield WIMPs which interact weakly with each other and ordinary matter (hence the hope of detecting them at all). We also expect (though the reason for this is more theoretical) that the universe may contain approximately equal amounts of WIMPs and anti-WIMPs. They wouldn't annihilate much because of their weak interactions, but in places where WIMP density is unusually high (the galactic center, WIMPs captured in the sun's core, etc.) you might see a gamma ray signal from WIMP annihilation. Gamma ray astronomers are looking for this sort of indirect evidence, and some even claim to see a signal.
I apologize, the last statement was arrogant and wasn't needed. I was reacting to the "if I don't understand it then those fancy scientists must be wrong" card that I hear played far too often, which often comes from a different sort of arrogance. My end point was that I don't know of other explanations that are just as plausible, and that there actually is a great deal of evidence. The exact identity of dark matter is, of course, still a mystery, and it's even possible that this whole concept will be replaced by something much more interesting.
The thing that makes the dark matter explanation compelling is that it makes so many different observations work. We don't have to fine tune things so much - it all fits together. Here are some examples.
1. Galaxy rotation curves - you can watch the orbits of stars in a galaxy to determine the distribution of matter in the galaxy. This shows that there is a lot more matter than can be accounted for by the stars and that it is distributed differently.
2. Gravitational lensing - you can see how light is bent by distant galaxies to map out their matter distributions. Again, there's a lot more matter than the stars can account for, distributed differently.
3. The cosmic microwave background - this one is complicated, but the idea is that you look at the "afterglow" of the big bang, released when the universe was as dense and hot as the surface of a star. We understand the physics of matter at these temperatures very well, and by studying the signatures of vibrations in this hot plasma, we can measure the properties of the early universe. We can see from this that the universe contains a lot of matter, and that the large majority of this matter is not composed of ordinary atoms (hard to explain, but fairly rock solid).
4. Light elements - Most of the universe's helium, deuterium, lithium and beryllium were created in the early universe, not in stars (the conditions aren't right). Again, the physics is very well-understood, nothing fancy. By studying the relative ratios of these elements, we can figure out the properties of the plasma in which they were formed (a bit hotter and you get less deuterium, the temperature falls too quick and you get less helium, stuff like that). Again, the universe has a lot of matter, and most of it isn't made of atoms.
5. Structure formation - if you work things out on supercomputers, you find that (if the universe containst only ordinary matter) the universe hasn't been around long enough to form the galaxies and galaxy superclusters that we see. Adding dark matter to the mix makes galaxies form faster - just enough faster!
And the beautiful thing is that all of these different arguments give essentially the same answer for the amount of dark matter and its basic behavior. You can tweak your theories to explain some of these observations, but no one has been able to explain them all - except with dark matter, the SIMPLEST explanation!!
Before you say something is "clearly inferior intellectual flotsam", learn what you're talking about...
A particle is only detectable if it interacts with your detector - it doesn't matter very much if it's heavy or light. Matter is almost entirely empty space (think about the space inside an atom between nucleus and electron), and so a particle should just pass through atomic matter unless it "reaches out and grabs" the electrons or nucleus. Protons, electrons, and most ordinary particles do just this - they interact strongly with matter, either via electric charge or the strong nuclear force. Dark matter particles are expected to be like neutrinos, only heavier - they interact so weakly that billions can pass through your body every second and never interact.
It's true we should consider the possibility that our model of gravity is wrong, and some physicists are working on just this idea. The thing to remember is that there isn't just one observation that general relativity and dark matter are meant to explain - there are an enormous number of different kinds of measurements, ranging from star orbits to gravitational lensing to the abundances of light elements in the universe. It's actually very difficult to tweak (or even completely rewrite) our gravitational theory in such a way that it does away with dark matter and yet makes all the observations work so precisely. It might be true that our model of gravity is wrong, but dark matter is actually the SIMPLEST explanation we know of for the amazing stuff we see in the universe, not some kind of weird idea that's getting ruled out.
Umm... no one HAS ever observed anything travelling faster than light. People have built particle accelerators that try their darndest to make things go as fast as possible, and they only hit 0.9999.... times the speed of light. That's a triumph of relativity, not a failure. And all the mass dilation effects, etc. all come out exactly as predicted...
The standard model doesn't give any real _wrong_ answers that I know of. There is the nasty detail that most field theory calculations give infinity if you do them naively, but there are well-defined ways to deal with those infinities and calculate finite answers, which are almost invariably correct. The only possible exception that springs to mind is the recent Brookhaven result about the muon's magnetic moment, but that's still being verified.
I would say that the problems come in the questions that the standard model can't answer - things that aren't within its scope. The standard model can't tell you the mass of the electron or the behavior of gravity - it's not that it gives the wrong answer, it's just that these are things you have to put in by hand, they aren't things the model is able to explain. Assumably we will someday be able to do experiments which are accurate enough that the standard model will give the wrong answer, just like it took a long time to construct an experiment for which classical mechanics gave the wrong answer.
It's worth noting that this experiment is fairly unlikely to give us any sort of answer about string theory. Physicists don't really understand string theory enough to determine whether it predicts any sort of signal that could be detected in this way - some theorists think it might, others disagree. It 's pretty likely that this experiment won't see anything new at all, in fact, but it's still important. If it sees nothing, we may be able to rule out some theories (though maybe not, since theorists are clever), and if it does we'll have discovered something truly remarkable. Science reporters seem to like to say that everything in physics is all about testing string theory, but there's more to it than that. In 10 years we may say string theory was crazy, or that it's right but has nothing to do with this sort of experiment. The point is to learn something about the universe, to see what rules it follows on different scales. We'll never know until we try it!
It's not so much that Einstein's relativity is wrong so much that it's incomplete. General relativity (and special relativity) have passed with flying colors every test we've ever put them to. Quantum field theory (the framework of particle physics) has done at least as well (in fact, it predicts some numbers in nature to more than 10 decimal places - far better than general relativity!). These theories are GOOD - they give the right answers. The problem is that both are incomplete in some way we don't quite understand. There are fundamental problems with making a quantum field theory of gravity - the two frameworks are very different, and they don't play well together. I wouldn't say that either is "wrong", they're just both incomplete. Both theories are probably nearly-perfect approximations to some sort of underlying framework (for example, string theory). Since neither theory can be the whole story, we expect that when we impose difficult enough tests on either one, they will begin to break down slightly - the world won't quite do what the theory seems to say. This is an excellent way to look for clues as to how these two frameworks fit together. You can look at this as an extension to relativity or a replacement for it.
My random theory is that the reason that the U.S. gets a lot of crackpots has a bit to do with our history. We're taught from elementary school on up that the U.S. was founded on the democratic notion that the "common man" is equal to (or better than) whoever is in power at the time. This populism is great for a lot of reasons, but it also means its hardly surprising Americans don't trust authority figures. Many people feel that an ordinary person with common sense could walk right in and show the snotty types who think they know everything that they're doing things all wrong. So we get people who think that evolution contradicts the "common sense" of the Bible, quantum mechanics contradicts classical common sense, etc. and that whatever weird ideas they have are better. Some people think that, since they're as good as anyone else, if they don't understand something then it must be wrong.
I second that observation - I'm one of the only physicists on my experiment who doesn't use a Mac laptop! OS X has a lot of appeal in many parts of the science community - it allows a user the ability to transparently use a lot of unix/linux functionality (ssh, xwindows, etc) to deal with workstations and data servers and yet gives you a fun, slick user interface when you want it. Not to mention that Mac laptops, while somewhat delicate, are very nice.
The solution to the problem you mention first (how come the light hasn't already passed us) is that the universe is bigger than its current "horizon size" (the distance light could have traveled since the big bang). We can't see anything beyond the horizon, but that doesn't mean it isn't there. The light that our immediate neighborhood emitted 13 billion years ago has long since passed us, but there are points 13 billion light years away whose light has just had time to reach us today.
The way that the universe ends up bigger than its horizon is explained by the theory of inflation. The idea is that the universe expanded faster than light (distances grew exponentially rapidly, in fact) for a tiny fraction of a second after the bang, expanding by a factor of 10^50 or so in 10^-30 seconds. Since the expansion was faster than light, some points ended up far enough away that their light hasn't yet had time to reach us. This is not as ridiculous and contrived an idea as it sounds - there's actually a number of good particle physics ideas that could make things like this happen, and it's the only known way to explain a lot of our observations of the universe (including the one we're talking about now). The idea is accepted in some form or another by essentially all cosmologists.
As another poster mentioned, there doesn't need to be an edge or a center - imagine you're an ant on the surface of an inflating balloon. It will feel like everything on the surface is rushing away from you uniformly, regardless of where you are on the surface.
The fact that galaxies get "slapped together so quickly" is actually a rather good piece of the evidence for the existence of dark matter. The amount of visible matter in an ordinary galaxy (or galaxy cluster - most of these simulations are actually done with clusters and not individual galaxies) would actually take quite a bit longer to form than what we observe. These objects form because the occasional bit of the gas in the universe is slightly more dense than the neighboring bits, and that clump will tend to attract other bits by gravity and grow. The growth rate gets faster as the clump gets bigger (and hence exerts a stronger gravitational pull). We can get an idea of the size of the original "clumps" in the gas by looking at the patters of hot and cold spots in the cosmic microwave background (the leftover "heat" of the early universe), and they're not big enough for galaxies and clusters to form so quickly. Here's where dark matter comes in. If there's extra "stuff" in the universe that isn't visible, then galaxies are actually a lot heftier than they seem and are able to grow much faster. There's a lot more to it than that, but this is the basic idea.
As far as we understand it, there is no "edge" to the universe - at least not one we're expecting to ever be able to see. The universe as we know it has been around for about 13 billion years since the big bang. During that time, light has only been able to travel a certain distance - 13 billion light years (there are some technicalities with the fact that the universe is expanding as the light is traveling, but that's the gist). So we don't expect to ever be able to see farther than that distance, and most theories predict that the universe inflates (expands really fast) early in its life and so is actually much bigger than that distance. So if there is an edge, it's so far away light hasn't had the chance to get here from there. However, we can't even see that far. Earlier in the universe's history, it was much hotter and denser. Until about 300,000 years after the big bang, it was so hot and dense that it was opaque to light - light from before that epoch isn't able to travel very far without scattering, and can't reach our eyes. We can, however, see the last light that was released from the hot, dense gas just as the universe became transparent - this is seen as the cosmic microwave background. After that, the universe was very dark and homogenous - there were no stars or galaxies, and hence nothing for us to see! This period is called the "dark ages", for obvious reasons. After some hundreds of millions of years, gravity caused gas to clump together enough to produce the first stars and galaxies. These are the earliest things (other than the microwave background) that we could hope to study in a telescope picture. Some theories suggest that these might be weird objects - supermassive stars a hundred times bigger than our sun, bizzare protogalaxies, etc. - and they'll definitely teach us a lot about how galaxies form. So it's not the "edge", but it's probably quite near the edge of what we'll ever see.
I agree, it's very possible that some basic notion of ours about gravity is wrong - dark energy is very possibly a manifestation of that. This doesn't mean the stuff on the webpage you link to is any good. The main page contains such crap as an attempt to use "logic, mathematics, and geometry" to explain why the constitution isn't working, how propulsion systems for UFOs work, and so on. This is yet another example of someone thinking they can provide a "simple" explanation for the scientific phenomenon-of-the-week without bothering to learn any real facts about what he's trying to explain. Such stuff almost invariably makes no physical predictions and gives you no way to calculate anything important - it's just pseudological bluster. Science is hard, and it works a lot better than some armchair philosophers seem to think - if you want to make a contribution, learn something about it.
You're right, the natural step when we learn that the universe doesn't obey Newton's laws should be to try to modify Newton's laws, not to imagine that there is a magic 95% of the universe with funny unobserved properties. The thing is that this isn't the only evidence for dark matter. There are a number of different lines of evidence which lead to the same conclusion - the orbital behaviors of galaxies and their clusters, the adundances of various light elements in the universe, the behavior of the cosmic microwave background, x-ray emission from clusters, etc. It turns out that no matter how hard we try, we can't modify Newton's laws to get the right answer to all of these. Gravitational lensing (the bending of light by the mass of distant galaxies and clusters) is really impressive in this regard - modifying Newton's laws (and general relativity) in the desired ways should have essentially no effect on it, and it definitely looks like there's dark matter (and even allows us to map its distribution). Dark matter really seems like the SIMPLEST answer, from the point of view of someone who knows the data! Dark energy was the subject of the article, however, and that's quite a bit different. As of right now, I'd say that we DON'T have very convincing evidence that this isn't just a modification of general relativity. All of our particle physics-related ideas seem far too complicated. Oh, and chaotic systems still obey the laws of classical physics - the systems are just so complicated that knowing how the individual atoms are behaving is not very helpful for predicting the behavior of the macroscopic system.
Dark energy certainly acts a bit like antigravity, but it's generally not believed to be quite that. We really have no clue of its exact nature, however - we just know vaguely what it does. The usual suggestion (which dates in some ways back to Einstein, though he never guessed at dark energy) is that it's a cosmological constant - an additional term in the equations of general relativity. Others suggest it's a new kind of particle field. Either way, it has negative pressure. The details of negative pressure are a little confusing, but the gist is that if dark energy is the dominant form of energy/matter in the universe, the universe will expand nearly exponentially rapidly. It's not really an antigravity force, but it is really strange.
The fact that the universe is accelerating is not the same as the "big rip". The accelerating universe, as we understand it now, sort of means that the space between everything and everything else is getting bigger all the time. However, in order to discover this (and the expansion of the universe in general), we have to look at very distant galaxies - we don't see our own galaxy flying apart, and some other galaxies bound together in our local galaxy cluster are orbiting or moving toward ours. In general, objects that are in bound states - whether gravitational bound states (like solar systems and galaxies) or other bound states (atoms, etc.) will remain held together even as the distant galaxies which are not tightly bound to us zoom away. Our own situation on earth would be completely unaffected - you'd need a big telescope to even tell the difference. The idea of the "Big Rip" is that this condition that "bound things stay bound" (the dominant energy condition) might be violated, that dark energy might be so extreme that not even bound objects could keep from eventually dissipating. That idea is HIGHLY theoretical - there's no particular evidence for it, and until recently most theorists thought it was ridiculous. But, of course, this is science - we have to think about even the weird possibilities.
As a previous poster said, a galaxy like ours takes a couple hundred million years to rotate, and formation times tend to be on that order, also. The fact that this galaxy exists so early is, in some ways, evidence for the existence of Cold Dark Matter (CDM) - a population of heavy elementary particles that we think comprises much of the universe's "missing mass". The argument is that if CDM didn't exist, then galaxies (and more importantly, galaxy clusters) would take a very long time to form - the gas dynamics of the early universe tends to resist their collapse. CDM provides a way out of this - the dark matter isn't affected by any of that, and it can collapse more quickly to form big "seeds" for galaxies to form around once the gas cools down.