High Energy Physics - Supersymmetry, Mini Black Holes, Higher Dimensions & More!

[forgot password]

Very interesting thread, dude. 2 thumbs up!!!!! I'm just a backyard astronomer and my knowledge of quantum mechanics and other fields of advanced physics has more holes than a Swiss chees so some questions about the universe have been bugging me, hopefully you can help me clear them up . Ok, here's the 1st question: According to S. Hawking in his newest book, The Grand Design, Feynman's Sum Over Histories leads to the idea that our universe doesn't have a unique history that is independent of the observer, and there might be histories in which stars are made of all kinds of crap other than hydrogen and helium as in our present universe. I've been royally mind f**ked by this idea, it just doesn't make sense, I mean common sense. Would you mind elaborating on this alternative-histories-of-the-universe matter? What do some physicists at CERN think about Hawking's comment?

[kidd]

Wow, IcyFox works at CERN.

[kidd]

Incidentally, energy and mass are actually different aspects of the same thing (to wit, E=mc^2), but in this case the formula is E=pc, because photons are massless.

What does p stand for?

E=mc^2=pc.

Does that mean p=mc?

[patricia n]

do you think cern will attempt to make blackholes? should they make blackholes? a large group of physicists disagree with hawking's evaporation theory. i mean, have we even discovered an unstable black hole (not static)? of course one can argue that we can't discover it because it's too unstable to be observed, but how do we even know it exists?

if hawking is wrong about the evaporation theory then there may be no such thing as an unstable black hole. or if his numbers are gross overestimation and cern were to create one based on hawkin's numbers then the black hole will be too stable and expand as it consumes all matter around it including our planet.

sorry, i had something much more detailed but spcnet signed me out before i could post it and lost everything.

ps most of this came from my discussion with my hubby who found your first point about having a safe radius unsettling as blackholes feed on all things around it and will grow, thus there is no such thing as a safe radius for a man made black hole (since that radius will grow).

[IcyFox]

Hi all, some of the topics discussed here will take quite some time for me to explain; please excuse me for addressing the easiest topic first.

Wow, IcyFox works at CERN.

Yes.

[patricia n]

Hi all, some of the topics discussed here will take quite some time for me to explain; please excuse me for addressing the easiest topic first.



Yes.

lmao...taking the easy way out.

[IcyFox]

Very interesting thread, dude. 2 thumbs up!!!!! I'm just a backyard astronomer and my knowledge of quantum mechanics and other fields of advanced physics has more holes than a Swiss chees so some questions about the universe have been bugging me, hopefully you can help me clear them up . Ok, here's the 1st question: According to S. Hawking in his newest book, The Grand Design, Feynman's Sum Over Histories leads to the idea that our universe doesn't have a unique history that is independent of the observer, and there might be histories in which stars are made of all kinds of crap other than hydrogen and helium as in our present universe. I've been royally mind f**ked by this idea, it just doesn't make sense, I mean common sense. Would you mind elaborating on this alternative-histories-of-the-universe matter? What do some physicists at CERN think about Hawking's comment?

OK, let me first explain what Feynman's Sum Over Histories does before I discuss how Hawking applies that to the Universe(s).

The idea is this - suppose you want to get from your TV to your fridge for a snack, you'd take the shortest way possible rather than cycle throughout the whole neighbourhood first (usually). But when it comes to sub-atomic particles like electrons, not only do they occasionally stray into ridiculous routes to get from point A to B, they 'travel' via the alternate routes all at once!

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The method of calculating the probability of a particle starting from point A ending up at point B is to sum over all the individual paths (see example diagram) - hence the name Sum Over Histories. Of course, as with getting from the TV to the fridge, some paths are more probable than others.

At this point I can frankly state that I don't follow Hawking's work that closely, but I think he is applying this method not only to single particles but in fact the Universe itself, treating the whole Universe like a giant 'electron'.

This would mean that the Universe is 'evolving' via all possible paths at once, but we happen to find ourselves following the Universe along one particular path. Which in turn means there are alternate realities out there moving along separate paths, even if the probability of those paths are lower than ours.

However! I should stress on the "possible" in "all possible paths". This means that the path should at least be physically possible, meaning that you won't find paths where the Sun is made of green eggs and ham!

Finally, I should mention that physicists, like doctors or lawyers, also have our own specializations. While there are some CERN physicists who do research on cosmology - Hawking's field, the majority of the physicists here focus on high energy particle physics, based on my personal experience at least.

[IcyFox]

What does p stand for?

E=mc^2=pc.

Does that mean p=mc?

Actually, the 2 equations are not equal, but belong to the complete equation
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Where 'p' represents the momentum (vector).

If the object has no momentum (think lazy cat on sofa), then the equation reduces to the famous E=mc^2. On the other hand, if the object has no mass, like a photon, then the equation reduces to E=pc.

At this point, you might wonder, shouldn't p=mv? If m=0, how can a photon have monentum then? The thing is, when you go into the relativistic realm (at really high energies), energy and momentum are exactly conserved quantities, while mass is not.

After testing Einstein's idea for a decade, Compton conclusively showed that light can carry off some momentum after scattering with particles. (Of course, 10 years is a long time; he did other things as well.) This means that not only can light bounce off a particle, a particle can also bounce off light!

[Banh Mi]

So if we scale it up, can enough concentrated light bounce of say a person or a planet?

[patricia n]

I have a very difficult time accepting that there are many parallel universes out there. I think if you get down to the nitty gritty of physics and explore the abstracts of physics then anything is possible. It's such an interesting concept and if true then I envy the me who is a martial artist who's kicking butt in a different universe and pity the me who works at a brothel in another universe. So my question for you is....


What do you do at CERN...your job in particular?

[IcyFox]

do you think cern will attempt to make blackholes? should they make blackholes? a large group of physicists disagree with hawking's evaporation theory. i mean, have we even discovered an unstable black hole (not static)? of course one can argue that we can't discover it because it's too unstable to be observed, but how do we even know it exists?

if hawking is wrong about the evaporation theory then there may be no such thing as an unstable black hole. or if his numbers are gross overestimation and cern were to create one based on hawkin's numbers then the black hole will be too stable and expand as it consumes all matter around it including our planet.

sorry, i had something much more detailed but spcnet signed me out before i could post it and lost everything.

ps most of this came from my discussion with my hubby who found your first point about having a safe radius unsettling as blackholes feed on all things around it and will grow, thus there is no such thing as a safe radius for a man made black hole (since that radius will grow).

Erm, pretty much everything you mentioned here is wrong.

First, let's go back to the question, what makes a black hole a black hole? As long as something exerts a gravitational field so strong that no object, including light, can escape once it falls in, then it has succeeded as a black hole. The crucial point is that the gravitational field does not need to be infinitely strong, only strong enough to prevent light from escaping. So, the gravitational field of a black hole looks something like this.

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We also know that many galaxies, including our own Milky Way, have a supermassive black hole at the centre. But if we can't see the black hole because it traps light, how can we tell that it's there? By inferring from the stars orbiting around the black hole (see diagram below). Observe the sharp turns at the common focus of all the orbits. This means that there's something there that's both very small and very strong in gravitational field - just the right qualities for a successful black hole.

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Therefore, this also means that black holes do have a safe radius. BUT. If an object strays beyond the safe boundary, then it's a different matter altogether, and the astrophysics guys came up with a term for this: "spaghettification". The image below, taken by the Hubble Space Telescope, shows the jet signature of a high speed jet ejected when a black hole has its dinner.

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Coming back to the question of black hole evaporation by Hawking radiation, I looked up the literature and was surprised to find that while observations carried out so far on outer space black holes indicate that Hawking is correct, they are as yet inconclusive. However, there are other considerations, besides direct detection of Hawking radiation, that are strongly in favour of Hawking's calculations, such as conservation of energy and thermodynamics.

As for whether CERN is attempting to make black holes, I think I would oversimplify CERN's goals for the LHC like this: Collide the particles together at really high energy, then ask, "Oooh, what was that?"


Attached image: Orbits.png

[IcyFox]

So if we scale it up, can enough concentrated light bounce of say a person or a planet?

Yep. As a matter of fact, Feynman explored the possibility of using this as a source of fuel for rocket propulsion in one of his lectures. I shall now apply that to the case of a bouncing person with a rather simple approximation.

Suppose a 50kg person is standing still and you want to make the person bounce back at the speed of 1m/s, so you shine lots of light at the person's stomach or something, how much energy would you need in the light?

We use p=mv for the person (since the person is not travelling close to the speed of light), so the momentum we need to pass to that person is 50kg m/s (ignoring the effects of friction or gravity in this rough approximation).

So for 50kg m/s of momentum, we use E=pc (and assume 100% transfer efficiency), and the energy required would be 50kg m/s X 300,000,000m/s, or 15,000,000,000 J.

In comparison, a baseball hitting the person at 140km/h requires only about 100 J.

[Banh Mi]

Awesome. So would that much light feel like touching a wall? Getting pushed by a slow vehicle? And say if you keep reflecting that light back and forth in a system of perfect reflective senses, something like light in a diamond. Could you make a permanent forcefield assume the light doesn't lose any energy moving from lens to lens?

[IcyFox]

I have a very difficult time accepting that there are many parallel universes out there. I think if you get down to the nitty gritty of physics and explore the abstracts of physics then anything is possible. It's such an interesting concept and if true then I envy the me who is a martial artist who's kicking butt in a different universe and pity the me who works at a brothel in another universe. So my question for you is....


What do you do at CERN...your job in particular?

Background Info

CERN, being an international scientific organization, maintains a long-standing policy of inviting collaborators from nations all over the world to take part in research work carried out at the facilities here in Switzerland. With this policy, many of the scientists at CERN hold dual appointments here and at their home institutions.

As for me, my home institution is based in Singapore and I'm currently attached to the theory group at CMS under the tutelage of Italian and Belgian scientists, while my boss is Greek. Yep, I'm really a junior apprentice here because I don't have a PhD (yet), but I have no complains because the work is facinating, plus CERN pays quite well.


My Job Right Now

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I'm doing computer simulations to study multiple-parton interactions in the proton collisions, in particular what they call the 3jet+gamma event (see diagram). The challenging thing about proton collisions is that the proton sub-structure is built on quarks which interact in a really complicated way when the protons collide.

As a result, we can't really calculate many interesting quantities from 1st principles, which in this case is a framework known as quantum chromodynamics. This is where the computers come in to do the brute-force number crunching, and my job is to babysit the simulations while they're running, and figure out what to do if they puke funny results.

When the theory guys finally understand these interactions at the back of their hands (or when the experimental guys give up waiting for us), CERN will upgrade the LHC to its maximum energy and we can start exploring the exciting new physics.


3jetgamma.gif

[IcyFox]

Awesome. So would that much light feel like touching a wall? Getting pushed by a slow vehicle?

Edit: OK I get what you mean now. Getting pushed by another person seems more accurate.

And say if you keep reflecting that light back and forth in a system of perfect reflective senses, something like light in a diamond. Could you make a permanent forcefield assume the light doesn't lose any energy moving from lens to lens?

Yes, you could, but you probably missed the tongue-in-cheek nature of my previous reply. The force-field created by light trapped in a perfectly reflective box (not diamond) would be so weak you might as well not have it at all. I mean, if you shine a torchlight at yourself, you may find the light glaring, but you definitely won't get thrown backwards into the wall! (See above.)

[Banh Mi]

Yeah, I get that it's impractical, it's just that being moved by light is just so bizzare. Would it feel like a solid object? It would be like those sci fi force fields that you can touch without being burned to death.

[IcyFox]

Hahaha I don't know how it should feel like. Like the wind maybe? I mean, it shouldn't have any texture or shape etc. that you can grab.

[IcyFox]

Hi all, here's a new documentary series by Discovery.



Part 2: http://www.youtube.com/watch?v=mJ3ffZEar8Y
Part 3: http://www.youtube.com/watch?v=rGnUw2JL6sM
Part 4: http://www.youtube.com/watch?v=mpEUejJmphY

Enjoy and blow your mind!


BTW, I'd be very happy to discuss the science, but I'd rather not comment on any faith/religion matters.

[forgot password]

Hi Fox, thank you for answering my question about Feynman's Sum Over Histories. I'm still a bit puzzled by it, I mean how is it possible that a particle takes _various paths simultaneously_ to go from point A to point B? This just doesn't make sense in classical mechanics. A particle is just an inanimate object, how can it divide itself into many parts then, after having them travel many different paths of different lengths at once _with the same amounts of time_, combine them together to form the original particle at the designated destination?

[IcyFox]

Hi, sorry I missed your question for some time.

The key to the whole problem here is that at the sub-atomic level, the particles are NOT classical objects obeying the laws of classical mechanics!

At this scale, particles do not behave like marbles where it would of course be senseless to talk about the marbles dividing and re-combining, etc. But instead, the particles can behave like particles, OR, like waves.

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The above image shows single electrons fired through a double-slit. As you can see, over time, the electrons form a diffraction pattern - the signature of wave behaviour. This is clearest indication that the single electrons can split up at the slit, interfere with itself, then re-combine on the other side and hit the screen.

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Compare that with the interference pattern of water waves.