Ask a physicist anything. (6)

[Wiccan_Child]

Are the spirals in this picture anything to do with particle "spin"? What about the dots and lines?

The curves are lines of bubbles formed when particles passed through the inside of the bubble chamber. It's in a magnetic field, so electrons are bent to one side of the chamber (depending on how the field is set up), and positrons are bent to the other. As they lose momentum, they spiral inwards - that's probably what those tight spirals are, electrons losing momentum.

But it's not related to quantum spin, no.

EDIT: Chalnoth beat me to it

 

[Wiccan_Child]

Doesn't a singularity have non-zero volume? A single point is till volume, is it not?

It depends. I think Chalnoth would disagree with me on this, but basically General Relativity doesn't prohibit matter from being squeezed into effectively single point of zero volume, while Quantum Mechanics does have prohibit this. In both cases the mass is squeezed very densely indeed, but QM places limits on just how tight it can go.

A single point would be volume-less, though. It's a zero-dimensional object, and volume incorporates (at least) three dimensions. A flat 2D plane has area, but not volume, as there's no third dimension.

Here you have created a false dichotomy. You provided a perfect illustration to understand the majority of people around you, (your partner's love) but for that to help you need to realize said majority has a partner you do not perceive. They (we) have a basis for the same kind of trust you write about in your partner. And each of us truly do have to recognize that G-d has indeed earned said trust.

From my point of view, he has done nothing to earn my trust. I'm sure theologians could list endless reasons as to why he hasn't done anything, but the fact remains: he's done nothing. You can't simply assert that trust has been earned. Even if I believed the whole crucifixion and salvation thing was real, I'd still be sceptical about trusting a being that would go through such a series of events. I have reason to trust my parents, but not God. I can trust my parents will help me in a time of need, but I can't say the same thing about God, can I?

 

[Wiccan_Child]

On the other hand, you can also do an analysis of literal genesis, of which the Flood would be the easiest to understand. What are the consequences of a worldwide flood, specifically with respect to genetics, patterns of species distribution, the effects on plants and on aquatic animals requiring a specific salinity range. There's gonna be some very specific consequences that would leave definite evidence.

Indeed - and, conspicuously, there is none.

Since this subject is almost never worth discussing, I'll just leave it at that. The evidence is clear for those who wish to follow it, but those who wish to cover their eyes and believe what they want to believe will continue to do so.

A comment that cryptic could be a snide retort to either side of the debate

 

[Naraoia]

Another way to look at it is that we currently are living in a universe that is increasing in entropy. There had to be some sort of interesting event that generated the original low-entropy state.

Given your views on zeroes and infinities, I don't suppose you think infinitely increasing entropy (that "started from" negative infinity) is possible?

Also As I suspect that if the Multiverse theory were proven; Will this mean that each universe will have its own creator and thus God is not alone?

Speaking of which, is the multiverse idea ever going to be testable?

The curves are lines of bubbles formed when particles passed through the inside of the bubble chamber.

OK, my next stupid question. Can you see antimatter in a bubble chamber? This occurred to me when Chalnoth started talking about the pair of pions in that picture. If a positron enters the chamber, does it just annihilate with the nearest electron (the chamber is filled with ordinary matter, after all), or do you actually get a nice spiral track?

 

[Cabal]

OK, my next stupid question. Can you see antimatter in a bubble chamber? This occurred to me when Chalnoth started talking about the pair of pions in that picture. If a positron enters the chamber, does it just annihilate with the nearest electron (the chamber is filled with ordinary matter, after all), or do you actually get a nice spiral track?

Yes, you can.

FileositronDiscovery.jpg - Wikipedia, the free encyclopedia

The two tracks are an electron and a positron pair, both deviated by similar amounts but in opposite directions due to their difference in charge. (Ok, it's a cloud chamber, not a bubble chamber....)

Also lol at inadvertant smiley in URL.

 

[Naraoia]

Yes, you can.

FileositronDiscovery.jpg - Wikipedia, the free encyclopedia

The two tracks are an electron and a positron pair, both deviated by similar amounts but in opposite directions due to their difference in charge. (Ok, it's a cloud chamber, not a bubble chamber....)

Two tracks? I only see one

Also lol at inadvertant smiley in URL.

Far less annoying than an inadvertent [wash my mouth]

 

[Cabal]

Two tracks? I only see one

Sorry, that was vague. I was referring to the two tracks arcing away from the thick line cutting across the middle of the circle, starting quite close to the centre. They're quite fine.

The tracks are pretty much equal in trajectory but in opposite directions, which I suspect means they're being deviated by a uniform magnetic field. The trajectories are effectively equal as the mass of an electron is the same as the the mass of a positron, but the opposite change explains the different directions.

As for the odds of seeing this, I'm not sure. It's possible this was Anderson's best image - I would have thought there'd be some statistical likelihood of a collision with matter given a particular pressure in the chamber, perhaps this is an outlier case.

Far less annoying than an inadvertent [wash my mouth]

I wonder if you can still say the word that means laughing and sounds very like "snickering" without the norty words filter kicking in.

 

[Naraoia]

Sorry, that was vague. I was referring to the two tracks arcing away from the thick line cutting across the middle of the circle, starting quite close to the centre. They're quite fine.

I thought that was one line with a portion of it obscured by the thick line.

I wonder if you can still say the word that means laughing and sounds very like "snickering" without the norty words filter kicking in.

I only tried it once, and it didn't work. Wait... *tries with preview*... Still filtered out.

 

[Cabal]

I thought that was one line with a portion of it obscured by the thick line.

Yes, I'm an idiot. It is just a positron trail. The issue is the curvature corresponds to a positive particle but one far light than a proton, given the direction of the chamber field. I thought there was pair production going on, but I must be thinking of another image than this one.

Here, you know what, here's Anderson's paper, it's not that scary, and it will save you from listening to me get it wrong Phys. Rev. 43, 491 (1933): The Positive Electron

 

[Chalnoth]

Given your views on zeroes and infinities, I don't suppose you think infinitely increasing entropy (that "started from" negative infinity) is possible?

Haha, nope One of the fundamental facts about the laws of physics is that they are time-reversible. So you can just as sensibly talk about a system going backward in time as forward. Having a system that has consistent increase in entropy only makes sense if you impose a low-entropy boundary condition at early times. If you try to make the increase in entropy last an infinite time with no beginning, well, then you have an infinitely-low entropy to explain infinitely far into the past, making the whole problem vastly worse.

Speaking of which, is the multiverse idea ever going to be testable?

Directly? Not sure. But the way we can be sure a multiverse idea is true is by demonstrating the validity of a physical theory by experiments here on Earth which unambiguously predicts a multiverse.

Turns out we already have that theory: the standard model of particle physics says that the electroweak symmetry breaking event was a sort of "spontaneous symmetry breaking". Spontaneous symmetry breaking is an accident in the past of our universe which impacts the low-energy laws of physics we experience today. This pretty unambiguously predicts that other regions of space-time will have broken this symmetry in different ways, and so they will experience different weak force interactions (which has impacts on things like nuclear decays and various nuclear reactions in particular).

Now, we might doubt that the theory can be extended that far, but my bet is that as we learn more about fundamental physics, we will discover more and more such situations, to the point where it can no longer be denied that there exist other regions of space-time with different low-energy laws of physics.

OK, my next stupid question. Can you see antimatter in a bubble chamber? This occurred to me when Chalnoth started talking about the pair of pions in that picture. If a positron enters the chamber, does it just annihilate with the nearest electron (the chamber is filled with ordinary matter, after all), or do you actually get a nice spiral track?

Yes, absolutely. Anti-matter tends to corkscrew in the opposite direction of normal matter of the same type, because it has opposite charge. The opposite charge causes it to bend in the opposite direction due to the magnetic field. The anti-matter has to slow down before it has an appreciable chance of annihilating, so you see tracks that are just as long (and when an electron-positron pair annihilate, they produce a pair of photons that just leave the bubble chamber entirely).

 

[Naraoia]

Yes, I'm an idiot. It is just a positron trail. The issue is the curvature corresponds to a positive particle but one far light than a proton, given the direction of the chamber field. I thought there was pair production going on, but I must be thinking of another image than this one.

Here, you know what, here's Anderson's paper, it's not that scary, and it will save you from listening to me get it wrong Phys. Rev. 43, 491 (1933): The Positive Electron

Thanks I rather like the term "negatron". A pity it didn't stick.

Haha, nope One of the fundamental facts about the laws of physics is that they are time-reversible. So you can just as sensibly talk about a system going backward in time as forward. Having a system that has consistent increase in entropy only makes sense if you impose a low-entropy boundary condition at early times. If you try to make the increase in entropy last an infinite time with no beginning, well, then you have an infinitely-low entropy to explain infinitely far into the past, making the whole problem vastly worse.

Oh, bother

Directly? Not sure. But the way we can be sure a multiverse idea is true is by demonstrating the validity of a physical theory by experiments here on Earth which unambiguously predicts a multiverse.

Turns out we already have that theory: the standard model of particle physics says that the electroweak symmetry breaking event was a sort of "spontaneous symmetry breaking". Spontaneous symmetry breaking is an accident in the past of our universe which impacts the low-energy laws of physics we experience today. This pretty unambiguously predicts that other regions of space-time will have broken this symmetry in different ways, and so they will experience different weak force interactions (which has impacts on things like nuclear decays and various nuclear reactions in particular).

Now, we might doubt that the theory can be extended that far, but my bet is that as we learn more about fundamental physics, we will discover more and more such situations, to the point where it can no longer be denied that there exist other regions of space-time with different low-energy laws of physics.

That brings me to roughly the only philosophical question that absolutely intrigues me - the relationship between mathematics and physical reality.

It gives me such a pleasantly spooky feeling when a theory predicts something that no one has ever seen... but in this case, we may never see that something. So does the fact that theories allow more possible universes that we observe mean that these universes CAN exist, does it mean they MUST exist, that something is missing from the theory, or that not everything about a theory needs to say something about reality?

Incidentally, wouldn't the same reasoning support the many worlds interpretation of QM? It seems like a similar situation on a smaller scale to me. Aren't you basically inducing a spontaneous symmetry breaking event whenever you force a particle to "choose" one of its possible states by observation?

I'm getting way out of my scientific comfort zone here

Yes, absolutely. Anti-matter tends to corkscrew in the opposite direction of normal matter of the same type, because it has opposite charge. The opposite charge causes it to bend in the opposite direction due to the magnetic field. The anti-matter has to slow down before it has an appreciable chance of annihilating, so you see tracks that are just as long (and when an electron-positron pair annihilate, they produce a pair of photons that just leave the bubble chamber entirely).

Thanks!

(I guess I should have figured out that they leave traces - antiparticles were discovered somehow, after all. )

 

[Naraoia]

Enjoy: Through the Wormhole: Does Time Exist? | Watch Free Documentary Online

Incidentally, I'm watching this right now, and there's a bit I didn't understand. How exactly would the observation that physical laws change in different parts of the universe prove that time is real?

 

[Chalnoth]

That brings me to roughly the only philosophical question that absolutely intrigues me - the relationship between mathematics and physical reality.

It gives me such a pleasantly spooky feeling when a theory predicts something that no one has ever seen... but in this case, we may never see that something. So does the fact that theories allow more possible universes that we observe mean that these universes CAN exist, does it mean they MUST exist, that something is missing from the theory, or that not everything about a theory needs to say something about reality?

Well, the way I like to think about it is that we shouldn't complain when a theory predicts something we can't test. We should, instead, worry about the things we can test about the theory. If this has definite implications about things we can't test, well, we should accept that: we're not infinitely powerful, and never will be, and shouldn't allow our own practical limitations keep us from considering theories that happen to predict some things we can't actually test. Just focus on the testable components and leave it at that.

Incidentally, wouldn't the same reasoning support the many worlds interpretation of QM? It seems like a similar situation on a smaller scale to me. Aren't you basically inducing a spontaneous symmetry breaking event whenever you force a particle to "choose" one of its possible states by observation?

I'm getting way out of my scientific comfort zone here

Hehe Well, yes, the many worlds of quantum mechanics is similar. First, it is the simplest explanation for our observations (because it makes no assumption of wavefunction collapse), and by that metric alone the most likely. The second point is that within the many worlds interpretation, wavefunction collapse is independent of observation: wavefunction collapse happens by interaction of the system in question with a larger system. This is my favorite experimental paper on the subject:
Phys. Rev. Lett. 77, 4887 (1996): Observing the Progressive Decoherence of the “Meter” in a Quantum Measurement

Basically, they set up the equivalent of a double-slit experiment, where they're using a radiation field to collapse the wavefunction of the atoms. They don't ever observe this radiation field, so there is no observation driving the collapse. It is simply the interaction between the atoms and the radiation field which drives the collapse.

Furthermore, in the many worlds, there is no "choice" of state. It is simply that the different states of the particle lose the ability to communicate with one another. The system remains in the full superposition it started in, but each observer within the quantum system can only obtain information about its own portion of the whole superposition.

That is, if there is an observation of a quantum system with two possible states A and B, then when an observer looks at the system he will be in a superposition of two states: system is in state A and observer observes state A, system is in state B and observer observes state B. So with everything happening, there just isn't any choice.

(I guess I should have figured out that they leave traces - antiparticles were discovered somehow, after all. )

Hehe

 

[razeontherock]

Here's something I understand:

From my point of view, he [G-d] has done nothing to earn my trust.

I have reason to trust my parents, but not God.

Your response was to my statement of "we;" which you knowingly and intentionally exclude yourself from, as indicated by your Faith icon. Interesting comparison though. I would definitely not trust my parents. As such, you can't imagine how difficult it is for me to even approach anything like trust in G-d. Likewise, a "natural" part of Christianity is to 'please the Father;' a completely foreign concept to me. So then, the notion that there might be anything I could do that would in any way "please G-d;" yeah I can't really wrap my head around that ...

Something I really don't understand:

A single point would be volume-less, though. It's a zero-dimensional object

It seems to me that in order for an object to be an object, it must have volume.

 

[Wiccan_Child]

Here's something I understand:



Your response was to my statement of "we;" which you knowingly and intentionally exclude yourself from, as indicated by your Faith icon. Interesting comparison though. I would definitely not trust my parents. As such, you can't imagine how difficult it is for me to even approach anything like trust in G-d. Likewise, a "natural" part of Christianity is to 'please the Father;' a completely foreign concept to me. So then, the notion that there might be anything I could do that would in any way "please G-d;" yeah I can't really wrap my head around that ...

It seems awfully conceited of God to send people into the furnace for not deigning to please him...

It seems to me that in order for an object to be an object, it must have volume.

Not necessarily. The universe is a weird place. We don't really know what electrons look like; they could be spheres, they could be squashed spheres, they could be point particles with no volume or shape whatsoever.

 

[GrowingSmaller]

I can imagine a domino topple going on and on for miles away from me talking time to go from start to finish. What about affecting elementary particles - if I hit a table is there a domino topple chain reaction going to ever smaller particles that takes tome to come into being?

 

[Chalnoth]

I can imagine a domino topple going on and on for miles away from me talking time to go from start to finish. What about affecting elementary particles - if I hit a table is there a domino topple chain reaction going to ever smaller particles that takes tome to come into being?

Yup, exactly! It's a pressure wave, also known as a sound wave

 

[Wiccan_Child]

I can imagine a domino topple going on and on for miles away from me talking time to go from start to finish. What about affecting elementary particles - if I hit a table is there a domino topple chain reaction going to ever smaller particles that takes tome to come into being?

Pretty much. The speed of sound is basically a measure of how fast a disturbance or perturbation in one atom or molecule gets transferred to its neighbour. The faster the transference, the faster sound travels through that medium.

I remember thinking about the speed of light, and what would happen if you had a pair of scissors many light years long, but a normal handle. If you closed the handle suddenly, wouldn't the far ends of the blades travel at faster than the speed of light? Turns out, no: relativity manifests as a limiting factor in the blade. Assuming the scissors didn't shatter, you'd have a shockwave as the metal moved down over time. Same sort of thing.

 

[hasone]

When is the Higgs boson either going to reveal itself or be ruled out?

I've been waiting since I first learned of its possible existence a whole, like, ten years ago.

When are we getting our quantum computers?

I want to hack RSA.

Why do stupid scientists have to work so slowly that they won't be able to answer all my questions before I die?

I want my answers now.

Why is science so cool? Why can I spend 5 hours straight doing nothing but reading research papers and call it fun?

 

[mzungu]

WOW!!! I mean WOW!!!!!: http://www.popsci.com/node/55542/?cmpid=enews072111