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I'm a Particle Astrophysicist, ask me anything

Author
Tsadkiel
Aliastra
Gallente Federation
#381 - 2012-03-24 03:40:46 UTC
Professor Alphane wrote:
Tsadkiel wrote:
Professor Alphane wrote:
RE: Stopped light - the fact matter can slow light to me implies something can interact with the beam and slow it, over a possibly infinite space surely this decelaration must = total , ie loss of momentum.. so yes basically what I am suggesting is that this beam will deteriote into your blob of random EM eventually.

You say that light has some property to self perpatuate, that sort of goes against my thoughts that nothing is truely infinite other than 'change' .


i've said it before and i'll say it again, you can be as uncomfortable with the scientific results all you want, but that wont change the nature of the universe.

yes, light is self propagating. this comes directly from Maxwell's equations when applying them as a solution to the wave equation. a changing E field can induce a changing B field which can induce a changing E field etc...

the other thing to note that the slowing down of light i am referring to in my previous post is a change in its velocity when it enters a medium, not the continual deceleration of light. we have no evidence to support the latter. light traveling at c enters a medium where the speed of light is 1 m/s, the light will start traveling at 1 m/s and keep traveling at 1 m/s until it is absorbed or it leaves the medium.

as for the spinning toy thing, i've never heard of this. now, it IS true that that space-time curves in the presence of energy densities (and mass carries a great deal of it, hence Newtonian gravitation). we have indeed proved this in the lab and it implies that a compressed spring is ever so slightly "heavier" than an uncompressed spring, but to see this at a macroscopic level, and in a toy non the less, makes me suspicious. do you have a link to this thing? i would love to read about it! =D



I'll need to do some searching to find the link to that toy, I saw one at christmas when I was shopping for my son but can't remeber what it called itself.

Still your description of light is hard to reconcile to my mind what you now describe is a perfect resonating 'pertual motion' entity that while being influenced in velocity by enviroment doesn't lose it's perfectly phased and balanced wave unto the infinite. You are implying it is constant in everything but velocity but then it was earlier though it was of constant velocity.

Science is only the abiltiy to see what can be seen, but forever there is more that could be seen


Yes.

light changes only through interaction. there are materials with dispersion relations that affect the phase and frequency of light as it passes through them. but the light only "stops" when it is absorbed.
Selinate
#382 - 2012-03-24 03:44:39 UTC  |  Edited by: Selinate
I had some big long post about all the things you mentioned, but it didn't post correctly, and I'm not going to try to write it all out again...

Basically you're wrong about the ITER, I got my information from a more reliable source, a leading professor in the field of Plasma physics. The original date for completion was supposed to be about 2007, I think, but it got delayed by funding issues and such. That chart? Yeah, that's updated. It's not indicative of the original plan at all.

Also, no where on that page does it mention power production from the ITER to the power grid. In fact, it mentions a heat rejection system which just dumps the energy. My point about the power production of such a system is still VERY much valid with the problems it induces, and no, that is not a feasible power producing system for the very reasons I mentioned.

The longest part was about magnetic fields, but I don't want to type it all out again at all.
Tsadkiel
Aliastra
Gallente Federation
#383 - 2012-03-24 03:53:10 UTC
Selinate wrote:
I had some big long post about all the things you mentioned, but it didn't post correctly, and I'm not going to try to write it all out again...


no worries man. thanks for the excellent discussion though =D if you have anything else you would like to talk about i will do my best to contribute!
Selinate
#384 - 2012-03-24 04:03:07 UTC
Since you are a particle astrophysicist, I will now ask you a question that they never bothered to teach me.

Why does a neutron cross section have peaks and dips, while a cross section for something like a scattering reaction between two hydrogen atoms is essentially smooth?

Any detailed information is appreciated, as it actually helps me a lot.
Tsadkiel
Aliastra
Gallente Federation
#385 - 2012-03-24 04:27:12 UTC
Selinate wrote:
Since you are a particle astrophysicist, I will now ask you a question that they never bothered to teach me.

Why does a neutron cross section have peaks and dips, while a cross section for something like a scattering reaction between two hydrogen atoms is essentially smooth?

Any detailed information is appreciated, as it actually helps me a lot.


the specifics of the neutron cross section depends heavily on the target composition, but the long and short of it is that the spikiness is due to the absorption of the neutron within the target nucleus. there are only specific energies that a thermal neutron can carry in order to be absorbed and these are dependent, again, on the target element (predominantly the number of nucleons and the dimensions of the nucleus). this is why the absorption characteristic is spiky and not asymptotic or single peaked. scattering for hydrogen atoms, consisting of only charged particles, exhibit smooth cross sections because they are dominated by "soft" scattering as a result of their mutual repulsion.

hope this helps!
Whitehound
#386 - 2012-03-24 07:58:02 UTC
Tsadkiel wrote:
your statement concerning time as non independent dimension is actually a question currently being worked on at fermilab. it is basically the question of time being an illusion of motion or visa versa. if you like i can try and comment on this, though i know little about the current experiments.

How can I misquote you? You said it yourself... It is indeed an interesting question. The idea of independent dimensions comes from mathematics and therefore is not automatically true for our real world. If you find the time to look into it and can give some simple answers then I would appreciate it.

And thank you for your answers so far. I am glad that you did not answer my questions by just saying "Because we can." - a common answer to many questions, but not very inspiring and some physicist give it, because they think it is a cool answer. I rather hear a physicist say that he or she does not know, really. It is your job to find out after all.

Loss is meaningful. Therefore is the loss of meaning likewise meaningful. It is the source of all trolling.

Caldari Citizen20090217
Science and Trade Institute
Caldari State
#387 - 2012-03-24 16:19:13 UTC
Tsadkiel wrote:
inducing a charge in an object is certainly possible, but it would require you to physically move the charge from the source to the object. we can create coherent ion beams, so assuming the projectile can hold the charge, then, perhaps? the result would be soft scattering; the projectile would not immediately change direction as if it hit a wall, but rather, it would slowly change its trajectory along a smooth continuous path... in order to create effective shielding it would require massive MASSIVE field strengths. the exact values would depend on the momentum of the projectile and how much it needs to be scattered.


I'd be grateful if you could point me in the direction of some equations etc. that cover this? The relation between field strength, charge, mass + velocity of the particle and the resultant deflection just so I can plug values in and see how fail my concept was? Oops
Tsadkiel
Aliastra
Gallente Federation
#388 - 2012-03-25 04:44:37 UTC
Selinate

i had an epiphany today! i think i understand what you were trying to say about magnetic fields, and why i completely missed your point.

magnetic fields indeed do not induce forces radially towards or away from the field source on charged particles. instead they twist and turn charged particles with a velocity. from this perspective, yes, you are correct, magnetic fields "do not attract/repel" charged particles. they do not attract/repel charged particles in the same fashion as electric fields. i completely missed what you were trying to saybecause as soon as you stated that "magnetic fields do not attract" i immediately thought of counter examples.

i read

[quote]A magnetic field does not attract. It does not repel. That is an electric field. ... a particle only needs charge to respond to a magnetic field, in itself if a particle is still, it has no magnetic field.[/quote

this is what i thought of

it is possible to mathematically simulate magnetic monopoles. this is covered extensively in one of the text books i own, Classical Electrodynamics. it is basically done by examining the magnetic field near the end of a very long, very tightly wound solenoid. here the magnetic field is approximately radial, and will attract and repel other "magnetic monopoles" in the exact same way as electric charges.

i also came up with the classic example of two parallel current carrying wires. in this case the two wires create magnetic fields and they are either attracted or repelled by each other based on the relative direction of current flow. in this case, the forces acting on the charges that compose the currents in the wires are towards or away from each other. this shows how charges with velocity can exert forces on each other along lines connecting the two. this colinear force is created explicitly by the magnetic field induced by the moving charges

i think we are actually in complete agreement and i just misunderstood you. sorry!
Tsadkiel
Aliastra
Gallente Federation
#389 - 2012-03-25 05:03:44 UTC  |  Edited by: Tsadkiel
Caldari Citizen20090217 wrote:
Tsadkiel wrote:
inducing a charge in an object is certainly possible, but it would require you to physically move the charge from the source to the object. we can create coherent ion beams, so assuming the projectile can hold the charge, then, perhaps? the result would be soft scattering; the projectile would not immediately change direction as if it hit a wall, but rather, it would slowly change its trajectory along a smooth continuous path... in order to create effective shielding it would require massive MASSIVE field strengths. the exact values would depend on the momentum of the projectile and how much it needs to be scattered.


I'd be grateful if you could point me in the direction of some equations etc. that cover this? The relation between field strength, charge, mass + velocity of the particle and the resultant deflection just so I can plug values in and see how fail my concept was? Oops



it isn't just a plug and chug kind of problem :/ your idea isn't "fail" it just probably isn't feasible based on what we currently know.

a good first order method would be to calculate, for a given field E, how far a charge of Q with kinetic energy T would travel before coming to a complete halt. this will involve integrating the electric field over the distance from the firing point to some distance R away from the field source (assuming the field is radial). this result is related to the electrostatic potential. set this equal to the kinetic energy per unit charge of the projectile and just solve for R. this will be the distance away from the field source the projectile will stop. then you can just fiddle with the parameters to get the behavior you are interested in and VOILA! you have just completed your first mathematical model =D

you will need this and this as well as an understanding of rudimentary calculus.

good luck!
Pr1ncess Alia
Doomheim
#390 - 2012-03-25 05:31:57 UTC  |  Edited by: Pr1ncess Alia
These are very basic, (edit, and possibly filled with logical fallacies, especially that 2nd one) so let's pretend I'm not asking them.

My beer would like to ask the following questions:

-Does the impossibility of perpetual motion negate the possibility of an eternal universe?

-How can we reconcile the impossibility of perpetual motion with the knowledge that in a closed system, gross matter/energy always remains constant (never truly created or destroyed)

I like to think the universe pops, expands, contracts and pops again over and over and each time it happens I get a little higher top score on Ms. Pacman.

I just want to make sure science isn't going to rain on my theory.
Thank you in advance.
Selinate
#391 - 2012-03-25 19:04:21 UTC  |  Edited by: Selinate
Tsadkiel wrote:

Selinate

i had an epiphany today! i think i understand what you were trying to say about magnetic fields, and why i completely missed your point.

magnetic fields indeed do not induce forces radially towards or away from the field source on charged particles. instead they twist and turn charged particles with a velocity. from this perspective, yes, you are correct, magnetic fields "do not attract/repel" charged particles. they do not attract/repel charged particles in the same fashion as electric fields. i completely missed what you were trying to saybecause as soon as you stated that "magnetic fields do not attract" i immediately thought of counter examples.

i read

Quote:
A magnetic field does not attract. It does not repel. That is an electric field. ... a particle only needs charge to respond to a magnetic field, in itself if a particle is still, it has no magnetic field.


this is what i thought of

it is possible to mathematically simulate magnetic monopoles. this is covered extensively in one of the text books i own, Classical Electrodynamics. it is basically done by examining the magnetic field near the end of a very long, very tightly wound solenoid. here the magnetic field is approximately radial, and will attract and repel other "magnetic monopoles" in the exact same way as electric charges.

i also came up with the classic example of two parallel current carrying wires. in this case the two wires create magnetic fields and they are either attracted or repelled by each other based on the relative direction of current flow. in this case, the forces acting on the charges that compose the currents in the wires are towards or away from each other. this shows how charges with velocity can exert forces on each other along lines connecting the two. this colinear force is created explicitly by the magnetic field induced by the moving charges

i think we are actually in complete agreement and i just misunderstood you. sorry!



Yes, this is exactly the point that I was trying to convey, and I'm glad that's cleared up.

This is interesting that you speak of this solenoid. Is this realistic, or is it a property of when it approaches infinitely thin and infinitely long? This sort of information is more towards the electrodynamics of circuits and such, if I'm not mistaken, and that's something I'm more or less not really familiar with at all.

I also remember the case of two current carrying wires held in a parallel formation attracting or repelling each other. Honestly, it's been about 3 or 4 years since I went over that piece of information though, along with the rest of the classical electrodynamics that doesn't have to do with plasmas, and that set of physics is just based off of mostly the Maxwell equations and gaussian distributions.
Selinate
#392 - 2012-03-25 19:11:06 UTC
Pr1ncess Alia wrote:
These are very basic, (edit, and possibly filled with logical fallacies, especially that 2nd one) so let's pretend I'm not asking them.

My beer would like to ask the following questions:

-Does the impossibility of perpetual motion negate the possibility of an eternal universe?

-How can we reconcile the impossibility of perpetual motion with the knowledge that in a closed system, gross matter/energy always remains constant (never truly created or destroyed)

I like to think the universe pops, expands, contracts and pops again over and over and each time it happens I get a little higher top score on Ms. Pacman.

I just want to make sure science isn't going to rain on my theory.
Thank you in advance.


Perpetual motion itself isn't impossible. In fact, it's pretty much given in one of Newton's laws that perpetual motion is the norm unless something else acts upon it (unless there's some more modern physics that negate this that I'm unaware of). Perpetual motion devices are usually some sort of machine that is said to be able to "work" perpetually, I guess you could say. It's actually one of the laws of thermodynamics that negate this, though I can't remember which exactly, though I think it has to with entropy not being conserved overall and, in fact, always increases with every action you perform, where entropy really is a quantity that describes the inability to capture all energy within any given system for a certain task (this is the best way I can describe it, one of my professors literally called the explanation of entropy describing chaos as "horse ****")....
Whitehound
#393 - 2012-03-25 19:42:49 UTC
Selinate wrote:
Perpetual motion itself isn't impossible.

It is impossible. If you cannot prove that it exists, then the logical consequence is that you have proven the opposite.

Do not say that it exists only to have a point and then take it back again. That is horse ****.

Loss is meaningful. Therefore is the loss of meaning likewise meaningful. It is the source of all trolling.

Selinate
#394 - 2012-03-25 20:05:19 UTC
Whitehound wrote:
Selinate wrote:
Perpetual motion itself isn't impossible.

It is impossible. If you cannot prove that it exists, then the logical consequence is that you have proven the opposite.

Do not say that it exists only to have a point and then take it back again. That is horse ****.


Go ahead. Keep trolling. Show your lack of understanding.
Whitehound
#395 - 2012-03-25 20:39:10 UTC
Selinate wrote:
Whitehound wrote:
Selinate wrote:
Perpetual motion itself isn't impossible.

It is impossible. If you cannot prove that it exists, then the logical consequence is that you have proven the opposite.

Do not say that it exists only to have a point and then take it back again. That is horse ****.


Go ahead. Keep trolling. Show your lack of understanding.

Help me to understand you. Do you have proof of its existence?

Loss is meaningful. Therefore is the loss of meaning likewise meaningful. It is the source of all trolling.

Selinate
#396 - 2012-03-25 20:56:33 UTC
Whitehound wrote:
Selinate wrote:
Whitehound wrote:
Selinate wrote:
Perpetual motion itself isn't impossible.

It is impossible. If you cannot prove that it exists, then the logical consequence is that you have proven the opposite.

Do not say that it exists only to have a point and then take it back again. That is horse ****.


Go ahead. Keep trolling. Show your lack of understanding.

Help me to understand you. Do you have proof of its existence?


of perpetual motion? It's newton's first or second law, for christ's sake. An object that is in motion stays in motion unless acted upon by an external force.

Your entire original reply to my post is completely off the mark also as it manages to misunderstand everything I said in the post.
Whitehound
#397 - 2012-03-25 21:57:39 UTC
Selinate wrote:
of perpetual motion? It's newton's first or second law, for christ's sake. An object that is in motion stays in motion unless acted upon by an external force.

No, it is not a proof of its existence. Only because things can have a motion is it not a proof for a perpetual motion. It is an assumption we make and because we cannot prove its existence does it not exist. All that exists is motion itself.

Loss is meaningful. Therefore is the loss of meaning likewise meaningful. It is the source of all trolling.

Selinate
#398 - 2012-03-25 22:21:58 UTC
Whitehound wrote:
Selinate wrote:
of perpetual motion? It's newton's first or second law, for christ's sake. An object that is in motion stays in motion unless acted upon by an external force.

No, it is not a proof of its existence. Only because things can have a motion is it not a proof for a perpetual motion. It is an assumption we make and because we cannot prove its existence does it not exist. All that exists is motion itself.


I tell you what, you can argue that all you want (even though its logical fallacies are so strong, anybody with a brain could point them out), and I'll just not respond to you again.
Whitehound
#399 - 2012-03-25 22:42:07 UTC
Selinate wrote:
I tell you what, you can argue that all you want (even though its logical fallacies are so strong, anybody with a brain could point them out), and I'll just not respond to you again.

All you are telling me is that you have no proof and that you do not know when it is time to shut up.

Loss is meaningful. Therefore is the loss of meaning likewise meaningful. It is the source of all trolling.

Alpheias
The Khaleph
#400 - 2012-03-25 22:50:01 UTC  |  Edited by: Alpheias
Whitehound wrote:
Selinate wrote:
I tell you what, you can argue that all you want (even though its logical fallacies are so strong, anybody with a brain could point them out), and I'll just not respond to you again.

All you are telling me is that you have no proof and that you do not know when it is time to shut up.


I think Selinate just told you to come up with proof that perpetual motion does not exist, that the theory is wrong rather than dribble a little and splutter out that perpetual motion is wrong.

Agent of Chaos, Sower of Discord.

Don't talk to me unless you are IQ verified and certified with three references from non-family members. Please have your certificate of authenticity on hand.