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Comment RPV SUSY (Score 1) 61

Any SUSY is going to provide a dark matter candidate.

Actually that is not quite correct. A majority do but there are searches conducted at the LHC for something called R-parity violating SUSY. In these models the lightest SUSY particle can decay and SUSY does not explain Dark Matter.

These models are generally less popular because there are very strong limits on them from existing data. In particular these models allow for flavour changing neutral currents and thing like baryon number violation and there are extremely strong limits on both processes not being seen (although we do eventually expect to see baryon number violation).

Comment No assumption re: SUSY (Score 1) 61

Does the higher energy and luminosity have any real chance of creating dark matter that we didn't see at the lower energy

Nobody can really answer that: we are going beyond the energy frontier and nobody can really say for certain what, if anything, we will find. However if those two broad assumptions I stated above (weakly interacting and thermally produced) are true for Dark Matter then, barring some pathologically strange model for new physics, we should see Dark Matter whether it is from SUSY or something else.

The reason these assumptions put a limit on the mass is that the heavier the particle the earlier the universe will cool to the point that no more can be produced. If this happens really early on i.e. very massive particles, then these particles will be so dense that they will interact and annihilate back into whatever produced them and so there will be very few left, too few to explain Dark Matter. Similarly if they are too low in mass then there will be far more of them because they decouple from the universe later when it is less dense but then the lower mass per particle means that there is still not enough to explain Dark Matter.

For a weakly interacting particle this 'sweet spot' turns out to be within reach of the LHC. This makes no assumption whatsoever about Supersymmetry only that the particle interact with the weak force. However if they only interact through the Higgs then the mass will be higher or (worse) if via gravity then much, much higher. Another possibility is that Dark Matter was not thermally produced in which case you need to know the production mechanism to find out what it says about the mass.

Comment Higgs is in the Standard Model (Score 2) 61

Can you explain why it is found acceptable for the standard model to allow calculation of probabilities greater than one (one of the reasons the Higgs was proposed)?

The Standard Model does not allow for calculation of probabilities greater than one. The Higgs is part of the Standard Model and you only get this effect, called violation of unitarity, for processes like WW scattering if the Higgs is not there. Since the Higgs was found the SM is complete and there is no problem with violating unitarity.

Comment ~1 microsecond (Score 2) 61

Well assuming it takes a minute in a 650W microwave to cook your disgusting boiled sausage that's roughly 60*650=39kJ of energy, lets call it 40kJ. The LHC beams contain roughly 360MJ. The beams take roughly 90 microseconds to make a complete orbit (27km/3e8 m/s) so that is a power of roughly 4TW (=4 million MW).

Now the sausage is probably only about half a nuclear interaction length (guess) so only about 18% of the protons will interact per sausage crossing and not all of that energy will actually be converted into heat since much will go to secondaries. So lets be conservative and say that 1% of the incident energy heats the sausage. Hence the the time for the sausage to get 40kJ will be 40e3/(4e12*0.01) = 1 micro second.

Assuming the sausage absorbs 1% of the total beam energy (which will happen in under a millisecond) then it will have about 900 times more energy than it needed to cook it which is the energy released by slightly less than 1kg of TNT...and this is one of the reasons why the LHC is know as the Big Bang machine! ;-)

Comment Different...no firm prediction (Score 3, Insightful) 61

On the other hand, if no new physics is discovered, could this be the Michelson–Morley experiment of the 2000s?

That's probably very unlikely. Michelson-Morley was testing a prediction of the best understanding of light at the time. The non-observation of changes due to motion through the ether was clear evidence that the best understood theory for light was wrong.

Now we have found the Higgs the established model, called the Standard Model, has no more predictions to make: we have found it all. The problem is that there are some phenomena which the Standard Model cannot explain, like Dark Matter, and it relies on some amazing fine-tuning of parameters to have such a light Higgs (the odd of this happening by chance are about the same as winning a lottery 5-6 times in a row...and if someone did that nobody would believe it was simple luck!).

The solutions to these issues involve speculation by theorists and there are multiple candidates. Supersymmetry is probably the leading one but if we fail to see SUSY in the coming run then I, and a lot of my colleagues, will probably start to doubt it as the most likely explanation. However even then it might still be that SUSY is the explanation but at a higher energy scale that we can reach and just a more-than-minimal variety of it.

Personally the thing I expect the most for us to find is Dark Matter. this is based on two broad assumptions that cut across many different theoretical models: that Dark Matter interacts through the weak force and that it was thermally produced in the Big Bang. If these assumptions are correct then the mass of the Dark Matter particle has to be in reach of the LHC. However this is still far from any sort of guarantee: there are other models for Dark Matter out there with good motivation which we would not see e.g. axions.

Comment Conjecture (Score 3, Interesting) 205

baryons would have decayed

Actually that is conjecture as there is currently no evidence that protons decay. I'll grant that the expectation is that there are high energy processes which violate baryon number and if this is true then it should be possible for a proton to decay. However there is a simple way around this: suppose the initial conditions of the Big Bang just included a slight excess of baryons? No B violation is needed and protons are absolutely stable.

As you can probably guess I'm a particle physicist and not a cosmologist. However even in the dark energy models presumably a 'big rip' condition is reached in the voids between gravitationally bound objects since there is nothing to stop the acceleration? If so then surely the implications for the stable pockets is not really known since all our understanding of causal disconnection is based on GR which would no longer be valid in the regions between the galaxies.

Comment Why not Just Link Textbook Chapters? (Score 5, Insightful) 205

Rather than poorly written, mistake filled blog pages on basic physics why not just link chapters from a physics textbook? The content is the same, there would be fewer mistakes in the physics since books are reviewed and edited and the writing style is less annoying.

The blogger this time forgets to include the knowledge that the universe's expansion is accelerating. We learnt this about a decade ago so it's not exactly new. The problem is that as the rate of expansion increases the volume of the universe which you can travel to without exceeding the speed of light shrinks. Given enough time it will become smaller than atoms and then nuclei etc. until you get to the planck scale and then nobody knows what will happen since we need a working quantum model for space-time itself which does not yet exist.

Now whether heat death or the 'big rip' kills off intelligence first is probably not clear - and I'm not sure I would really believe anyone who claims to know given the unknowns. However since space-time itself has a limited lifespan then intelligence clearly has a limited lifespan too unless we eventually figure out a way to leave the universe. That might be a tricky problem but we do have a lot of time to try and figure out a solution

Comment Re:No interaction means you don't know (Score 1) 226

..but if there were some way to make sure the two "copies" do not interact with anything.

That's my entire point! If you assume that you can make a system where there is no interaction then there is absolutely no difference whatsoever for all concerned between position A or position B. Hence there is absolutely no way to know whether you are in position A or B until you interact so there is no magical "teleportation". It's the same as Schrodinger's cat: the cat is either alive or dead and you find out which when you open the box and there is no undetermined state as per the common misconception.

To get the EPR paradox you need an entangled state for two particles. What you have is a single, unknown state of one particle (or person). These are not the same.

Comment Too low: don't forget the power requirements! (Score 4, Insightful) 597

I can see AC to the doorstep a big efficient whole house power supply that has 12vdc and 48vdc rails that are distributed thorough the house and battery backed, and few 220v "appliance circuits" off the AC.

48V and 12V lines are far too low to be sage and/or sensible. Remember that the power used is equal to the voltage times the current and that the heating of the wire carrying the current goes as the square of that current. Typical house wiring is good for ~30A of current and supplies several plugs in a room typically. With a 12V circuit you limit the power of all the devices connected to this circuit to 360W vs. the 6.6kW you get now (or 3.3kW if you live in North America). Even with a 48V circuit you only get 1.44 kW.

The result is that either you need to rewire the entire house with massively thick, and therefore expensive, cables to carry the far higher currents or you need to use a higher voltage for transmission. Even the factor of two reduction between Europe and Canada/US is noticeable for some devices: electric heaters are far punier than their European counterparts, kettles take far longer to boil, and Electric lawnmowers are practically useless etc. If you drop the voltage by another factor of 2-10 below even Canada/US then almost all devices will be impacted.

Comment Skin effect: DC more deadly at same voltage (Score 2) 597

Because you can't electrocute people with DC?

Actually it is easier to electrocute someone with DC the reason it rarely, if ever, happens is because most DC sources are very low voltage and cannot drive enough current through a human body to be a problem. A high frequency, alternating current is actually relatively safe because of something called the skin effect where only the outer surface of the object conducts the current. For a human this confines the current to your skin and away from vital organs like your heart. It is the reason why Tesla himself could discharge lightning bolts from his fingers without being electrocuted. However you do have to be careful since where the spark leaves your body can get burnt due to the heat of the plasma created.

Comment Re:faster than light never violates Relativity (Score 1) 226

Relativity requres that nothing can move through space as fast as light (c).

Not correct - light moves through space as fast as light. Nothing can move faster.

nothing moving faster than light can slow down to c

Actually it is stronger than that - nothing moving faster than 'c' should exist because of causality. If something moving faster that 'c' exists then then some inertial frames it will be propagating backwards in time. We could then use whatever it is to communicate with the past and set up all sorts of nasty temporal paradoxes.

Comment No interaction means you don't know (Score 1) 226

but, for the intents and purposes of outside human observers, haven't you instantly blinked across light years?

If you entangle two states such that the position is the only thing different between the two states then there can be no interaction with either 'copy' which differentiates between the two possible positions. The instant that there is an interaction which determines which state you are in (position A or B) that is the position you are in. It is no more mysterious than putting some one at the centre of a (very large) box and have them move away from that centre at almost the speed of light in an unknown direction. The person in the box does not know which direction they are moving in because there is nothing surrounding them and the people outside do not know until they open the box.

Comment Can't un-invent them (Score 1) 69

You realise we came close to a full scale nuclear war at least three times during the cold war?

Yes - and if we could un-invent the things I'd be absolutely for that. However complete disarmament would not help with a cold war scenario like this since the tensions were so high that paranoia would set in an one side would worry that the other side was rebuilding its nuclear weapons in secret and so start their own re-armament program in secret.

This leads to a potentially even more dangerous situation than having two sides each with a known nuclear arsenal. If one side believes that they are the first to re-arm how much more likely are they to use the devices in a pre-emptive strike than they would if they new the other side could retaliate in kind? Probably the best situation we can hope for is a world where only a handful of nations possess the devices and where each of their arsenals is limited. This preserves the deterrent while minimizing the risk of accident, or even worse, theft. Fortunately this seems to be the situation we are in although it would be great if the nuclear nations to reduced their stockpiles of warheads further.

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