Freethought & Rationalism Archive

Jesse · 01-21-2003, 07:07 PM

cfgauss:
Well, why do we think we're moving down the river in the boat? Because we are. That's the relation, no more. It's trivial.

I still don't get your analogy. The issue is not that you're moving down the river, but that you remember parts of the river that you were on in the -t direction ('upstream') but you don't remember the parts you will be on in the +t direction ('downstream'). Why doesn't it work the opposite way? Would it work the opposite way if there was a low-entropy boundary condition in the +t direction but no such condition in the -t direction? If you think answering these questions is trivial, can you give me an explanation that's shorter than Hawking's?

Shadowy Man · 01-21-2003, 07:52 PM

Quote:

Originally posted by Osm bsm Y.
i haven't ever been taught what heat is aside from molecules vibrating.

if heat is related to motion in any way, shouldn't there be some relation between a particles ability heat and it's speed?

Hi Osm,

Yes, when you start talking about astrophysical environments, you need to think carefully about the words "heat" and "temperature". The word temperature can mean a few things.

In most cases you would say that temperature is a measure of the energy intrinsic to the motion of the particles. Imagine a gas with many particles, each particle has a different energy, but the distribution of energies of each particle is such that the ensemble has a certain average energy. This can be characterized by a "temperature"

The "heat" that cfgauss was referring to is the energy of the particles in the early universe. Two things kept atoms from forming. There were many particles with high enough energy that when they collided with an atom would cause the atom to dissociate. Additionally, there were enough high energy photons to dissociate atoms. Once the universe expanded enough, the energy density dropped enough so that the gas "cooled". Then atoms could form without being broken apart and photons were free to roam through the universe unimpeded (i.e. they didn't scatter off of any free electrons). This moment was called the "time of last scattering". What we see as the cosmic background radiation is these photons finally hitting the Earth, after being redshifted into the microwave part of the EM spectrum by the cosmological redshift.

Mr. Sammi · 01-22-2003, 06:25 AM

cfgauss,

when you claim that acceleration is not relative how do you propose to deal with measurements?

The cfgauss yardstick (ha ha).

Sammi Na Boodie ()

Mr. Sammi · 01-22-2003, 06:44 AM

I have found it more instructive to view SR and itz correspondence to reality USING the Mass to Energy ratio. This way I can ideally seperate intrinsic Mass(irreducible) from reducible Mass. Is there Mass life after a near-death-experience? Speeding mass to c is a near death experience for the mass because it should shed light if capable.

It may be clear to some of us that the liimit of SR and changes in Mass as Mass approaches the spped of light although mathematically infinite nevertheless has pratical limits.

There are two seperate frames of reference which must be considered, and I ask the learned cfgauss for an opinion. The first frame of reference is the frame of the motion, the second is the frame of the Mass. Pratically what this entails is the source of the motion, who is providing the impetus. Is it the mass itself that is providing itz own source of PUSH, or is it a source external to the mass which is providing the MOTION?

Depending on these TWO considerations the Mass will certainly behave iinaccordance to the TOPOLOGY of the system in motion. Perhaps the ESTEEMED cfgauss can provide a clear explaination *of* what should occur...

Sammi Na Boodie ()

Hawkingfan · 01-22-2003, 08:34 AM

Quote:

Originally posted by cfgauss
Do you understand what the "popular" in popular science means? It means "dumbed down so you can understand it without complexities and details."
E=mc^2 is only valid for an object at rest. If you talk about adding energy then it's not at rest, and you're talking about things in different frames. That kind of logic gets you confused as how you could get to Alpha Centauri, 4 ly away, in a weekend going near the speed of light.

The statment "space is made up of particles left over from particle/antiparticle annihilations" clearly implies that they are a product of it. If I were being nitpicky, like you claim, I would've pointed out that it doesn't make any sense to say that *space* it made of it.

I know what "popular" means. Please stop flattering yourself. I believe you, in fact, have difficulty understanding basics of physics. For instance, you could not identify that the original postings were talking about the 2nd LoT whenever this was totally obvious. You also did not understand the basics of relativity. You also were unfamiliar with the 3 arrows of time. I still disagree that anything can travel faster than the speed of light. I've heard this fact spoken from almost every physicist from Einstein to Hawking. E=mc^2 influenced the atom bomb, an object not at rest.

Hawkingfan · 01-22-2003, 08:46 AM

Quote:

Originally posted by cfgauss
The statment "space is made up of particles left over from particle/antiparticle annihilations" clearly implies that they are a product of it. If I were being nitpicky, like you claim, I would've pointed out that it doesn't make any sense to say that *space* it made of it.

Oh, and I almost forgot again, cf! May I be excused? You never did excuse me from my previous request. I AM ASKING FOR YOU TO EXCUSE ME!!! MAY I BE EXCUSED?!!!!!!!!!!!!!!!

Jesse · 01-22-2003, 10:03 AM

Mr. Sammi:
when you claim that acceleration is not relative how do you propose to deal with measurements?

Acceleration is not relative in SR--it is only inertial reference frames that are equivalent. Two people moving at constant velocity relative to each other will both say that the other one is aging more slowly--this is the basis of the twin "paradox." The resolution of the "paradox" is that in order for the two twins to meet up and see which one is really older, one of them has to accelerate to turn around, accelerating and no longer remaining in the same inertial reference frame.

cfgauss:
E=mc^2 is only valid for an object at rest.

Hawkingfan:
E=mc^2 influenced the atom bomb, an object not at rest.

cfgauss is correct, the complete formula is E^2 = p^2*c^2 + m^2*c^4, where p is the momentum and m is the rest mass. if p=0 this reduces to E=mc^2, but in general that's not true. For example, a photon has zero rest mass, but it still manages to have energy because of its momentum p.

Mr. Sammi · 01-22-2003, 10:24 AM

Jesse,

HUH? you really believe that solves the paradox. As far as I can tell the acceleration of one object in the twin-paradox situation defies SR. How does one accelerate out of c?

Besides from the perspective of the other dv dt will appear ...

and the answer is RELATIVE.

Sammi Na Boodie ()

Mr. Sammi · 01-22-2003, 10:31 AM

Jesse,

They are talking about two different things. Relative rest Mass and Mass in motion.

Try this thought experiment. A bubble ship wizzing around at .75c with an experiment on board which has a rare grade of plutonium. The plut is set in motion on the bubble ship. Which equations will apply, and when?

Sammi Na Boodie ()

Jesse · 01-22-2003, 10:47 AM

Mr. Sammi:
HUH? you really believe that solves the paradox. As far as I can tell the acceleration of one object in the twin-paradox situation defies SR. How does one accelerate out of c?

No one is moving at velocity c in the twin paradox. In the twin paradox, the two twins start out moving at some constant velocity away from each other--say, 0.9c--and then one of them accelerates until he's moving towards the other twin. Eventually they meet up, and they find that the twin who did the turning around is the one who actually aged less (strictly speaking it's not the acceleration that's important, it's just the fact that the twin who turns around does not stay in a single inertial reference frame).

Here's a good explanation of the twin paradox:

http://www.phys.unsw.edu.au/~jw/twin.html

and here's a simpler one:

http://kestrel.nmt.edu/~raymond/clas...ok/node43.html

Mr. Sammi:
Try this thought experiment. A bubble ship wizzing around at .75c with an experiment on board which has a rare grade of plutonium. The plut is set in motion on the bubble ship. Which equations will apply, and when?

You haven't given me an actual problem here. What quantity am I supposed to calculate? What do you mean by "set in motion"--what is its velocity? How is the fact that it's plutonium relevant to the problem?

In any case, if you're calculating energy in SR, E^2 = p^2*c^2 + m^2*c^4 is the only equation you need. E=mc^2 is just a special case of that equation, namely the one where p=0.

01-22-2003, 06:25 AM	#83
Mr. Sammi Banned Join Date: Jun 2002 Location: Montr�al Posts: 367	acceleration not relative cfgauss, when you claim that acceleration is not relative how do you propose to deal with measurements? The cfgauss yardstick (ha ha). Sammi Na Boodie ()

01-22-2003, 06:44 AM	#84
Mr. Sammi Banned Join Date: Jun 2002 Location: Montr�al Posts: 367	Mass to Energy ratio I have found it more instructive to view SR and itz correspondence to reality USING the Mass to Energy ratio. This way I can ideally seperate intrinsic Mass(irreducible) from reducible Mass. Is there Mass life after a near-death-experience? Speeding mass to c is a near death experience for the mass because it should shed light if capable. It may be clear to some of us that the liimit of SR and changes in Mass as Mass approaches the spped of light although mathematically infinite nevertheless has pratical limits. There are two seperate frames of reference which must be considered, and I ask the learned cfgauss for an opinion. The first frame of reference is the frame of the motion, the second is the frame of the Mass. Pratically what this entails is the source of the motion, who is providing the impetus. Is it the mass itself that is providing itz own source of PUSH, or is it a source external to the mass which is providing the MOTION? Depending on these TWO considerations the Mass will certainly behave iinaccordance to the TOPOLOGY of the system in motion. Perhaps the ESTEEMED cfgauss can provide a clear explaination of what should occur... Sammi Na Boodie ()

01-22-2003, 10:24 AM	#88
Mr. Sammi Banned Join Date: Jun 2002 Location: Montr�al Posts: 367	acceleration Jesse, HUH? you really believe that solves the paradox. As far as I can tell the acceleration of one object in the twin-paradox situation defies SR. How does one accelerate out of c? Besides from the perspective of the other dv dt will appear ... and the answer is RELATIVE. Sammi Na Boodie ()

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01-21-2003, 07:07 PM	#81
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	cfgauss: Well, why do we think we're moving down the river in the boat? Because we are. That's the relation, no more. It's trivial. I still don't get your analogy. The issue is not that you're moving down the river, but that you remember parts of the river that you were on in the -t direction ('upstream') but you don't remember the parts you will be on in the +t direction ('downstream'). Why doesn't it work the opposite way? Would it work the opposite way if there was a low-entropy boundary condition in the +t direction but no such condition in the -t direction? If you think answering these questions is trivial, can you give me an explanation that's shorter than Hawking's?

01-22-2003, 10:03 AM	#87
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	Mr. Sammi: when you claim that acceleration is not relative how do you propose to deal with measurements? Acceleration is not relative in SR--it is only inertial reference frames that are equivalent. Two people moving at constant velocity relative to each other will both say that the other one is aging more slowly--this is the basis of the twin "paradox." The resolution of the "paradox" is that in order for the two twins to meet up and see which one is really older, one of them has to accelerate to turn around, accelerating and no longer remaining in the same inertial reference frame. cfgauss: E=mc^2 is only valid for an object at rest. Hawkingfan: E=mc^2 influenced the atom bomb, an object not at rest. cfgauss is correct, the complete formula is E^2 = p^2c^2 + m^2c^4, where p is the momentum and m is the rest mass. if p=0 this reduces to E=mc^2, but in general that's not true. For example, a photon has zero rest mass, but it still manages to have energy because of its momentum p.

01-22-2003, 10:31 AM	#89
Mr. Sammi Banned Join Date: Jun 2002 Location: Montr�al Posts: 367	Jesse, They are talking about two different things. Relative rest Mass and Mass in motion. Try this thought experiment. A bubble ship wizzing around at .75c with an experiment on board which has a rare grade of plutonium. The plut is set in motion on the bubble ship. Which equations will apply, and when? Sammi Na Boodie ()

01-22-2003, 10:47 AM	#90
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	Mr. Sammi: HUH? you really believe that solves the paradox. As far as I can tell the acceleration of one object in the twin-paradox situation defies SR. How does one accelerate out of c? No one is moving at velocity c in the twin paradox. In the twin paradox, the two twins start out moving at some constant velocity away from each other--say, 0.9c--and then one of them accelerates until he's moving towards the other twin. Eventually they meet up, and they find that the twin who did the turning around is the one who actually aged less (strictly speaking it's not the acceleration that's important, it's just the fact that the twin who turns around does not stay in a single inertial reference frame). Here's a good explanation of the twin paradox: http://www.phys.unsw.edu.au/~jw/twin.html and here's a simpler one: http://kestrel.nmt.edu/~raymond/clas...ok/node43.html Mr. Sammi: Try this thought experiment. A bubble ship wizzing around at .75c with an experiment on board which has a rare grade of plutonium. The plut is set in motion on the bubble ship. Which equations will apply, and when? You haven't given me an actual problem here. What quantity am I supposed to calculate? What do you mean by "set in motion"--what is its velocity? How is the fact that it's plutonium relevant to the problem? In any case, if you're calculating energy in SR, E^2 = p^2c^2 + m^2c^4 is the only equation you need. E=mc^2 is just a special case of that equation, namely the one where p=0.

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