Ask any question you want about Physics

originally posted by: dragonridr

The one I think is most interesting to think about is a shadow unIverse. Basically dark matter doesn't interact without matter. But it does interact with itself. Picture an entire universe with dark stars and dark planets could even be dark people. And they are wondering why they can't find the missing mass in their universe either. Basically the theory goes were not looking for one particle to explain dark matter instead its just like our matter interacts and forms particles. Even would have their own version of photons. The only thing we do see is the gravitational effects. I read the is last year so I'll have to look back into it to see who's idea it was.

a movie script ?
sci-fi !!

originally posted by: KrzYma

originally posted by: dragonridr

The one I think is most interesting to think about is a shadow unIverse. Basically dark matter doesn't interact without matter. But it does interact with itself. Picture an entire universe with dark stars and dark planets could even be dark people. And they are wondering why they can't find the missing mass in their universe either. Basically the theory goes were not looking for one particle to explain dark matter instead its just like our matter interacts and forms particles. Even would have their own version of photons. The only thing we do see is the gravitational effects. I read the is last year so I'll have to look back into it to see who's idea it was.

a movie script ?
sci-fi !!

Sounds like it doesn't it that's why it's interesting to say the least. Here I found a new article on it.
www.scientificamerican.com...

a reply to: KrzYma

a movie script ?
sci-fi !!

A movie would require a plot.
Science fiction (the good kind) takes current theory/technology and examines its potential effects on society when extended.

originally posted by: Phage
a reply to: KrzYma

a movie script ?
sci-fi !!

A movie would require a plot.
Science fiction (the good kind) takes current theory/technology and examines its potential effects on society when extended.

The best Sci-fi stands the test of time even before discovery proves them right....

originally posted by: KrzYma
a reply to: Arbitrageur

could help me with some thoughts ?

so called antimatter particle was detected in a cloud chamber, right ?

For initial discovery of positron, yes, but cloud chambers were replaced by bubble chambers and then increasingly more sophisticated detectors.

any luck in creation pictures of anti-proton ?
somehow google is not showing any reel pictures of anti-proton trail in a gas chamber...
I would really like to compare them two.

If you're interested in discovery, it wasn't a cloud chamber but rather a photographic emulsion stack used to detect the anti-proton.Here's the famous image:

www2.lbl.gov...

This first image of an annihilation star, found in the photographic emulsion stack experiments led by Gerson Goldhaber of the Segrè group, confirmed the discovery of the antiproton. An antiproton enters from the top of the image and travels about 430 micrometers before meeting a proton. Nine charged particles emerge from their mutual annihilation.

Of course neither of those detection technologies are used any more. Instead of photographic emulsion stacks, modern detectors can input their data into computers which use software to analyze the data in 3D.

... if opposite charged particles attract and the same time annihilate,
how comes "positron" goes through led and just slows down ?
look how thick it is ?
so... annihilation or no annihilation ?
maybe error in code ?

Ordinary matter, even lead, is mostly empty space. The common analogy is if you put a marble at the center of a football stadium to represent the nucleus, the electrons would be like grains of sand in the bleachers. So what's between the marble and the bleachers? Space. So how hard is it for a grain of sand to pass between the marble and the other grains of sand in the bleachers?

The reason neutronium like the composition of a neutron star is so dense is because all that space is gone. A teaspoon of it would have the same mass as a huge mountain of ordinary matter, so the density of lead doesn't begin to compare with that.

The positron can avoid direct collision as it passes through the lead plate, but, what it can't avoid is interacting with the fields in the plate which cause it to slow down. The reason the lead plate is used is so the curvature of the track can be compared on either side, and by looking at which side has the greater curvature, we can deduce what direction the particle was traveling. This is important so we can tell the difference between a positron versus an electron traveling in the opposite direction.

originally posted by: Arbitrageur

Ordinary matter, even lead, is mostly empty space. The common analogy is if you put a marble at the center of a football stadium to represent the nucleus, the electrons would be like grains of sand in the bleachers. So what's between the marble and the bleachers? Space. So how hard is it for a grain of sand to pass between the marble and the other grains of sand in the bleachers?

The reason neutronium like the composition of a neutron star is so dense is because all that space is gone. A teaspoon of it would have the same mass as a huge mountain of ordinary matter, so the density of lead doesn't begin to compare with that.

The positron can avoid direct collision as it passes through the lead plate, but, what it can't avoid is interacting with the fields in the plate which cause it to slow down. The reason the lead plate is used is so the curvature of the track can be compared on either side, and by looking at which side has the greater curvature, we can deduce what direction the particle was traveling. This is important so we can tell the difference between a positron versus an electron traveling in the opposite direction.

hm...

Of the three common types of radiation given off by radioactive materials, alpha, beta and gamma, beta has the medium penetrating power and the medium ionising power. Although the beta particles given off by different radioactive materials vary in energy, most beta particles can be stopped by a few millimeters of aluminium. Being composed of charged particles, beta radiation is more strongly ionising than gamma radiation. When passing through matter, a beta particle is decelerated by electromagnetic interactions and may give off bremsstrahlung x-rays.

...this beta particles are negatively charged and are repelled by the electron cloud in atoms.
a thin plate of aluminum changes the trajectory enough to scatter or slow down those electrons.
This all is in an "repulsion mode"...

so... a 6mm led plate will "stop" electrons from passing through.

Positrons are attracted by the electrons and both annihilate.
A positron will not avoid collision, but intensify its attraction even more if closer to electrons.

You can't use the same analogy you are using for electrons and explain the trajectory of a positron the same way.

a reply to: KrzYma


You confused me are you trying to say alpha particles anihalate? They don't they are reflected away by the magnetic field. Beta particles being smaller penetrate further but again magnetic fields will repel them. And to stop gamma rays requires a collision since they have no mass and no charge.
Alpha particles are so easy to block because they are essentially a hydrogen nucleus. Meaning two protons and 2 nuetrons. The interaction is explained through Colombs law

originally posted by: KrzYma
...this beta particles are negatively charged and are repelled by the electron cloud in atoms.
a thin plate of aluminum changes the trajectory enough to scatter or slow down those electrons.
This all is in an "repulsion mode"...

so... a 6mm led plate will "stop" electrons from passing through.

How many will it stop? Some? All?

It depends on the energy of the electrons. If they are high energy it won't stop them all.

For an analogy, think about a bb. Put it in a straw and try to blow out the bb so it penetrates a piece of cardboard. It doesn't have much energy, so the cardboard stops the low energy bb. Put the bb in a powerful bb gun and fire it at high velocity. The cardboard won't stop it.

So you can't make a blanket statement that such and such a shield will stop such and such a particle without considering the energy of the particle, and even then what you can actually end up measuring is a percentage of the particles stopped by the shield. It's not all or nothing, so stop thinking all or nothing.

I said the aluminum would stop most electrons (or beta particles), I didn't say it would stop them all. Think about it, what does "most" mean? It means some of them are getting through, even if most are not. If the electrons are at an energy level that the shield stops 99% of them and you fire a million electrons, how many electrons go through the shield? What's 1% of a million?

Positrons are attracted by the electrons and both annihilate.
A positron will not avoid collision, but intensify its attraction even more if closer to electrons.

This is a very naive model of subatomic interactions.

Using your understanding of particle physics the LHC wouldn't work because the protons have like charges and like charges repel, therefore they would never collide with each other.

Obviously the LHC does work and at high energies the electrical attraction and repulsion of opposite or like charges doesn't have as much effect on collision rates as it would at lower energies. Therefore the protons DO collide with each other, even though they have the same charge and are electrically repelled.

So the energy of the particle is an important consideration which you don't seem to be taking into account in your analysis, and you also need to stop thinking in all or nothing terms, but rather think of percentages and statistics.

originally posted by: dragonridr
Alpha particles are so easy to block because they are essentially a hydrogen nucleus. Meaning two protons and 2 nuetrons. The interaction is explained through Colombs law

Sounds more like helium to me.

originally posted by: dragonridr
a reply to: KrzYma


You confused me are you trying to say alpha particles anihalate? They don't they are reflected away by the magnetic field. Beta particles being smaller penetrate further but again magnetic fields will repel them. And to stop gamma rays requires a collision since they have no mass and no charge.
Alpha particles are so easy to block because they are essentially a hydrogen nucleus. Meaning two protons and 2 nuetrons. The interaction is explained through Colombs law

...Positrons
You can't use the same analogy you are using for electrons and explain the trajectory of a positron the same way.

confusion gone ???

a reply to: Arbitrageur

positrons and anti-protons, remember ??

You switched back to electrons !

You don't understand that this mechanism you are talking about applies to electrons *beta radiation, but is reversed if we talk about antimatter.
An positron is attracted by the electrons and they both annihilate each other according to the theory...

again... Although the beta particles given off by different radioactive materials vary in energy, most beta particles can be stopped by a few millimeters of aluminium.
those are not my words, this is ms science

Why is there only one trail in those pictures of positrons and most important, also in the picture of anti-proton allegedly collision ??
The collision machine you posted a link to, produces hundreds thousands collisions, are you saying the apparatus was able to select and separate one and only one anti-proton for this picture ??

lucky picture indeed !!

originally posted by: KrzYma
You switched back to electrons !

You did that here:

again... Although the beta particles given off by different radioactive materials vary in energy, most beta particles can be stopped by a few millimeters of aluminium.
those are not my words, this is ms science

For all practical purposes, those are electrons. And if you're going to repeat what you said, so am I because my reply didn't sink in:

If the electrons are at an energy level that the shield stops 99% of them and you fire a million electrons, how many electrons go through the shield? What's 1% of a million?

Why is there only one trail in those pictures of positrons and most important, also in the picture of anti-proton allegedly collision ??
The collision machine you posted a link to, produces hundreds thousands collisions, are you saying the apparatus was able to select and separate one and only one anti-proton for this picture ??

A proton and anti-proton annihilation event gives off a lot of energy on the subatomic scale, so it's got a unique signature. Protons milling around aren't giving off such energy. So it's kind of like asking if 999,999 people light matches and 1 person sets off a nuke, how are you going to spot the one person setting off the nuke when all those other people lit matches?

Generally though if you've got lots of particles and you're interested in only a few of them, you set up some kind of filters to select the kinds of particles you're trying to observe. Protons aren't annihilating other protons so the annihilation event with an anti-proton is relatively unique due to the rarity of the anti-protons in that early experiment.

a reply to: Arbitrageur

a nuke between matches is good comparison.

look at the picture in the link you posted, it says...

An antiproton enters from the top of the image and travels about 430 micrometers before meeting a proton.

so there is a trail before the "collision" and trails after "collision" so what ?
why are large parts of that picture removed ? or is that more pictures composed together ?

So it's kind of like asking if 999,999 people light matches and 1 person sets off a nuke, how are you going to spot the one person setting off the nuke when all those other people lit matches?

before the collision it is still just a missing match, in the picture you can see it coming from the top, so why are you talking about how much energy is released at the collision ? this energy has nothing to do with the particle before collision. It leaves a trail before colliding.


this from the picture description again.

Nine charged particles emerge from their mutual annihilation.

well.. something hit the nucleus of Ag or Br and it cleaved into something else ejecting 9 charged particles,
looking at that picture I see 2 electrons and 8 protons ( one very short )
just like bowling ball... where is the annihilation ?

originally posted by: Bedlam

originally posted by: dragonridr
Alpha particles are so easy to block because they are essentially a hydrogen nucleus. Meaning two protons and 2 nuetrons. The interaction is explained through Colombs law

Sounds more like helium to me.

Good catch brain freeze lol it was late what can I say. Think I was to busy omg to figure out what he had a problem with exactly.

a reply to: KrzYma

Now I see your confusion they had to track it through 200 layers of emulsion. And then develop each one and then track it to the next plate. We know have sensors that do the same at the LHC. They are showing you the results not each individual plate.

a reply to: Bedlam

"the spot's energy is isolated by the convective flows below" and you know that how?

a reply to: KrzYma
You're in luck. Apparently when Goldhaber was 81 years old in 2005, he gave a presentation at the “50 Years of Antiprotons Anniversary Symposium” explaining how he did it 50 years earlier, so I'll let you read his explanation in his own words:

The Observation of Antiproton Annihilation by Gerson Goldhaber

a reply to: Arbitrageur

thanks for the link !

I'm into something for the next few days now, but I will post my thought on it later....

Black hole, i have a theory, even though just a theory. Could it just be sound in such a low tone it bends light into it?

originally posted by: yulka
Black hole, i have a theory, even though just a theory. Could it just be sound in such a low tone it bends light into it?

No.

Sound doesn't exist in a vacuum. And it doesn't bend light. And it's not gravity.