OK Relavists

[lethe]

Originally posted by Janus58
I said that there was enough info to answer the question: "Who is right, and why?" This does not require knowing the exact value of the accleration experienced by the one sample (you only need that if you want to figure out exactly how much the two samples differ, but this is already given in the question).

hmm...

i guess my problem is that the figures given in the problem assume that there is no acceleration, and as long as there is no acceleration, there is no requirement that the two observers agree on how much decay there has been.

i see what you mean now, ryans, when you say you are making an approximation.

OK, well then i guess this is OK. my apologies.

i would suggest that the problem should go like this: "the observer on the rocket radios ahead to his friend at home and says 'i am 25 light minutes from home, travelling at about 0.9c. i have 1 lb of uranium left.' and then the travelling observer will see 10 minutes pass, and the stationary observer will see 25 minutes pass. the stationary observer peeks through the window as his friend passes at 0.9c. as the travelling observer passes his friend, they look at the uranium, and see the same amount left. whose calculations were correct?"

or something like that. the problem is that they cannot compare simultaneous measurements unless they are at the same place, and they cannot be at the same place at the end, if they started at the same place too, unless there is some acceleration going on.

i see now what you meant when you said you wanted to ignore acceleration, it but it might be better to remove some of the ambiguity to keep from confusing people like.

that is all. now carry on with your problem.

 

[ryans]

Acceleration is not required. Fuck here's the answer to the problem.

The half-life of the U 239 is no longer 23.5 min for the observer on the ground, he must adjust the value for the fact that the sample is moving relativistically w.r.t. him. thus for him the half life would should be
t(1/2)= to(1/2)/sqrt(1-(v/c)^2)
= 53.912 min

plug that figure into your decay formula, i.e.

N=Aexp(-kt) where N is the amount of substance left, A is the initial amount of substance, k=ln2/t(1/2) and t is time.

You will get the same answer if you adjust observer 1's time to correct for the fact that he is observing a relativistic event and leave t(1/2) unchanged. Same shit really. I delibrately did not include pedantics w.r.t. acceleratio as that confuses the issue. Acceleration would add corrections to the values I calculated, but in this example the physics is essentially all there.

 

[lethe]

Originally posted by ryans
Acceleration is not required.
....
I delibrately did not include pedantics w.r.t. acceleratio as that confuses the issue. Acceleration would add corrections to the values I calculated, but in this example the physics is essentially all there.

i think acceleration deserves to be thought about. it changes the nature of the problem rather drastically. if you don t want to deal with it, you should explicitly exclude it. you certainly should not write a problem that needs to require acceleration to be physical, and then ask that acceleration be ignored.

just my opinion.

 

[ryans]

Lethe, we can calculate the quantities in question using acceleration , I have no doubt about that. The fact is the observer on the ground undergoes no acceleration (excluding gravity) and so in the end his calculation is fundementally flawed as he has not included time dilation into his calculation of the expected amount of U-239 remaining in the sample. O.K. lets say that we don't know what speed the rocket is travelling at, just that the 2 observers record different times that have passed. Since the observer is on the rocket, and always within the same frame as the U-239, his decay calculations remain unchanged. The observer calculates the wrong value as he has failed to take relativity into account. But how many people do you think here, can calculate time dialtion due to acceleration.
However acceleration does not change the fact that the observer on the ground has miscalculated

 

[lethe]

Originally posted by ryans
Lethe, we can calculate the quantities in question using acceleration , I have no doubt about that. The fact is the observer on the ground undergoes no acceleration (excluding gravity) and so in the end his calculation is fundementally flawed as he has not included time dilation into his calculation of the expected amount of U-239 remaining in the sample. O.K. lets say that we don't know what speed the rocket is travelling at, just that the 2 observers record different times that have passed. Since the observer is on the rocket, and always within the same frame as the U-239, his decay calculations remain unchanged. The observer calculates the wrong value as he has failed to take relativity into account. But how many people do you think here, can calculate time dialtion due to acceleration.
However acceleration does not change the fact that the observer on the ground has miscalculated

ryans, i understand how time dilation works.

now: if there is no acceleration, the problem is this. both observers are in inertial frames. the stationary observer, once he gets his act together, and takes into account the time dilation into account, sees the uranium decaying more slowly.

from the travelling observer s frame of reference, the stationary observer is moving at 0.9c. thus, he thinks the at-home observer is moving slowly, and therefore seeing the decay at an accelerated rate.

when the trip is over, the two observers predict different values for at-home stationary reference frame prediction of the amount decayed. even when they both account for time dilation.

this is what is known as the twin paradox.

i realize that you just want to ignore the corrections due to acceleration, but when you do so, you open up a whole new can of worms.

you have two choices here: you can pretend that this can of worms doesn t exist, and hope that MacM also pretends it doesn t exist, or you can ask the problem in such a way as to explicitly exclude accelerated reference frames.

you chose the first option. unfortunately, MacM did not make the same simplifying assumptions that you did, assumptions which lead to a paradox.

if there is no acceleration, then both reference frames are equally valid to solve this problem, and you will get two different answers, the way you phrased the problem. now perhaps MacM would not have realized this, and would not have attempted the problem from the other reference frame.

it is my opinion that it would have been better to phrase the problem in such a way as to exclude the twin paradox.

 

[ryans]

Cool. Lethe, sometimes you are to smart for your own good. But do you agree that essentially this problem is not resolvable without SR. as MacM might try to convince us?

 

[ryans]

What I mean by the above is that you read to deeply into the problem. You do see however what I was trying to demonstrate.

 

[lethe]

Originally posted by ryans
What I mean by the above is that you read to deeply into the problem. You do see however what I was trying to demonstrate.

yes, i do see how the problem is supposed to go. i didn t at first, and i jumped all over you for it, but after a little more thought, i see how it is supposed to look.

as long as no one else makes the assumptions i did, then it s a good problem. if you modified the wording of the problem slightly, it would be impervious to nit-pickers like myself.

by the way, the twin paradox and accelerated motion is easily soluble using only SR and a small amount of calculus. you do not need GR to treat the accelerated problem.

 

[ryans]

Consensus reached.

I would like to point out all you stubborn bastards how Lethe and I come to an agreement in a scientific manner, with both of us admitting that we had misinterpreted the other, and for myself, the admission that the problem may have had some severe approximations. At least in the end we both came to an agreement on the nature of the problem, by considering each others arguements.
From my point of view this doesn't happen enough here.

 

[MacM]

Opps

To All Responders,

I had not read the problem close enough in the first place. I see now that the U239 was nothing more than a glorified clock problem. My initial that was that we were calculating how much fuel would be consumed in the trip which would lhave required some clarification including accleration, gross ship weight and any g fields being climbed out of and efficiency of energy transfer.

Much to your surprise I could have calculated my problem; including the changing g loads, fuel loads etc. In light of some of the comments you might be surprised to know that I have had mechanical, electrical and nuclear engineering, including some calculus. But I have never in my life used calculus but I do algebra and at one time could do matrix but that was years ago.

There was no math in your problem that I could not have performed FYI. But there is math there that I definitely believe should not be there. Time dilation, like relavistic mass are illusions and not physical reality. Don't start with cosmics rays and atomic clock tests because they are measuring process changes, not time perse. HOWEVER, IT IS LIKELY THAT ACCELERATION WILL ALTER THE DECAY RATE OF THE U239 but that isn't even a time dilation issue.

Without acceleration affects the correct answer is the 50% decay in the 23.5 minutes. 50Kg. If that isn't your correct answer then you are muddying the problem with relavistic nonsense.

 

[lethe]

Re: Opps

Originally posted by MacM
To All Responders,

I had not read the problem close enough in the first place. I see now that the U239 was nothing more than a glorified clock problem. My initial that was that we were calculating how much fuel would be consumed in the trip which would lhave required some clarification including accleration, gross ship weight and any g fields being climbed out of and efficiency of energy transfer.

Much to your surprise I could have calculated my problem; including the changing g loads, fuel loads etc. In light of some of the comments you might be surprised to know that I have had mechanical, electrical and nuclear engineering, including some calculus. But I have never in my life used calculus but I do algebra and at one time could do matrix but that was years ago.

There was no math in your problem that I could not have performed FYI. But there is math there that I definitely believe should not be there. Time dilation, like relavistic mass are illusions and not physical reality. Don't start with cosmics rays and atomic clock tests because they are measuring process changes, not time perse. HOWEVER, IT IS LIKELY THAT ACCELERATION WILL ALTER THE DECAY RATE OF THE U239 but that isn't even a time dilation issue.

Without acceleration affects the correct answer is the 50% decay in the 23.5 minutes. 50Kg. If that isn't your correct answer then you are muddying the problem with relavistic nonsense.

huzzah! good form, Mac!

 

[ryans]

No it isn't. The observer on the rocket is correct. Thus if we initially had 100g of U-239, we have 73.933g of U-239 left upon return of the rocket, as he is always at rest w.r.t. the sample, and he is gone for a period of 10.24 mins. In his frame of reference, he observes nothing unusual about the behaviour of th esample, as he is subject everything the sample is.

 

[James R]

MacM:

<i>Time dilation, like relavistic mass are illusions and not physical reality. Don't start with cosmics rays and atomic clock tests because they are measuring process changes, not time perse.</i>

Ok then. Please explain to me how I can measure time per se, as opposed to "process changes", just so I know how to distinguish the two.

On another issue, you complain about the relativistic rocket example because it is calculated in the Earth reference frame, rather than the rocket frame. Let's look at reference frames for a minute, using an example given by Galileo in the 17th century.

You are in the cabin of a ship travelling in a straight line at constant speed across the ocean. Please give an example of an experiment you can do inside the cabin to show that the ship is moving rather than stationary.

 

[ryans]

In addition to James R's question, answer this without postulating the existance of the aether. It has not been detected and thus does not exist for answering this question, i.e you must use known accepted physics.

 

[MacM]

Time Dilation

ryans,

Without acceleration affects the correct answer is the 50% decay in the 23.5 minutes. 50Kg. If that isn't your correct answer then you are muddying the problem with relavistic nonsense. [unquote]

ANS: I believe I properly qualified my answer. I used 23.5 minutes because it was simple and because I do not accept time dilation. You had already given the answer and stated the time dilation so I could have given you your desired answer but I won't do that because as I stated you want to play relativity.

I prefer reality. If you believe linear motion affects clocks then you are certanly free to do so. I don't. Acceleration yes but not linear motion. The rocket, pilot and pile of U239 is at rest relative to itself and gives a damn less about the earth clock or Alpha Centuri clock. You are mixing perception with physical reality.

 

[ryans]

You are using your intuition to describe a phenomona that goes against intuition. It's not everyday that you experience relativistic motion, and so I can understand how an older man like yourself, who has always trusted his intuition, to get it wrong. It's all right Mac it's not your fault. And I'm sorry but in this instance, perception and reality are intwined. perception not being subjectiveness but relative motion. Have fun MacM being ignorant, because the REALITY is that these things are observed.

 

[MacM]

Wish I Knew

James R.,

Ok then. Please explain to me how I can measure time per se, as opposed to "process changes", just so I know how to distinguish the two.[unquote]


ANS: Wish I knew. You would be calling me up and asking me questions.

Actually, I tend to believe that time is also an illusion. Not a physical enity or tangiable dimension at all but merely a producet of energy transfers causing change (events), we catalog such changes and say time is passing.

On another issue, you complain about the relativistic rocket example because it is calculated in the Earth reference frame, rather than the rocket frame. Let's look at reference frames for a minute, using an example given by Galileo in the 17th century.

You are in the cabin of a ship travelling in a straight line at constant speed across the ocean. Please give an example of an experiment you can do inside the cabin to show that the ship is moving rather than stationary.[unquote]


ANS: You didn't say that I couldn't look out the portal but I don't think that is what you want to hear. I don't know your example but if it will enlighten me I'm all ears.

 

[MacM]

Laughable

ryans,

You are using your intuition to describe a phenomona that goes against intuition. It's not everyday that you experience relativistic motion, and so I can understand how an older man like yourself ,((here you made me chuckle)) who has always trusted his intuition, to get it wrong. It's all right Mac it's not your fault. And I'm sorry but in this instance, perception and reality are intwined. perception not being subjectiveness but relative motion. Have fun MacM being ignorant, because the REALITY is that these things are observed.[unquote]


ANS: It is a shame that these perceptions have alternative explanations which you refuse to consider and hang on to the concepts of antiquity based on lack of information and misinterpretation.


Also, according to relativity, all motion is relative and each can claim being at rest. When one claims the rest position all his physics are normal and unchanged. That is specifically the case with a rocket which is self-propelled and it cares less about the earth observers view or the view of little green men on a plaetoid coming at him at 99.9%c because neither alter his rockets performance. How they may see that performance is another issue but that is observational not reality. Reality is F=ma for the fuel, thrust engine and rocket load (which is unchanging throughout the process - that is no mass change occurs that alters the rockets performance).

PS: While I am not an aether proponent why is it that it would be unacceptable to refer to an aether simply because it has never been measured or seen? Do we not have numerous theories that initially evolve based on assumptions, that ultimately are then found to be correct. Such as predictiong certain sub-atomic particles. Of course. And why then do you think it is fine for you to advocate v=c as a limit of a self propelled rocket when it is neither physcially justifiable and certainly has never been tested?.

Double standards make conversation difficult and unproductive.

 

[zanket]

Originally posted by Martin B
That's a second naughty! Cosmological redshift is not motion through local space-time and hence apparent recession velocities are not restricted to c.

I’d really like to know: Why does cosmology acknowledge time dilation but seems to ignore length contraction? Time dilation is observed about receding supernovae. Length contraction and time dilation go hand in hand in relativity, so from our perspective these supernovae and their galaxies should be contracted along our line of sight through them. The space between the supernovae and us should likewise be contracted since these objects aren’t moving through local space-time; that is, in any radial direction from our perspective space itself and everything in it must be both length contracted and aging slower, both length and rate of time approaching zero as recession velocity approaches c. Hence recession velocities should be restricted to c and the entire universe should be observable to us if not for redshifts approaching infinity making objects all but invisible.

Considering just the time dilation, the aging rate of supernovae approaches zero as their recession velocities approach c. Aging at zero (a stopped clock) they could not recede, so it is easy to see that the upper limit on recession velocity is c. Considering length contraction as well seems to make the case airtight, because supernovae would contract to a length approaching zero as their recession velocity approached c, which in turn shows how an infinite amount of mass—an infinite universe—can fit within our observable universe, within its finite volume.

 

[ryans]

Then why have tachyons never been observed, even though they are predicted in theory and are well within the energies of our current accelerators? Why can't we see the edge of the universe? Why is the energy released in a nuclear event equal to (m(i)-m(f))c^2? What then prevents violation of casualty? Faster than c travel specifically predicts reverse time travel can be achieved simply by going faster than c. Why are there black holes? why is light red shifted in exact accordance with c being constant? If c wasn't constant, the shift would alter markedly? How did Dirac predict the existance of the positron?(relativistic quantum mechanics). What theory, based on the invariance of physical laws of inertial frames moving relatively to one another, predicts the 2 types of particles we see today, and the rules they observe? (relativistic quantum mechanics). You fool. you trust your intuition, based in the non-relativistic, non-quantum world, and I will trust the facts. Your view leads to paradox's, relativity solves them!!