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Topic: various physics questions (Read 21145 times) |
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Benny
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Re: various physics questions
« Reply #100 on: Jul 23rd, 2009, 1:53pm » |
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The estimation could be wrong. Why?
Because we need to make huge assumptions:
We need to assume that Caesar's last breath has been thoroughly mixed into the whole atmosphere and has not been permanently absorbed somewhere or lost in deep space.
It takes some time for the atmosphere to be recycled by dissolving in the oceans, seas, ... and then being released or being transpired by plant life.
How long? I do not know
Anyone?
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| « Last Edit: Jul 23rd, 2009, 1:55pm by Benny » |
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Benny
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Re: various physics questions
« Reply #101 on: Jul 23rd, 2009, 1:57pm » |
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I wanted to look at it this way:
Say you put 1 drop or red coloring in 1 gallon of water and stir.
In a matter of moments, the solution is pink.
And if you draw 1 teaspoon of water from the solution, it will contain some of the coloring.
Now, granted, the earth's atmosphere is a great deal more than 1 gallon. The air from Caesar's last breath has had about 2,000 years to thoroughly mix throughout the atmosphere, and there are billions and billions (do I sound like Carl Sagan?) of air molecules in one of your breaths, so it's close to certain that at least one of the molecules you inhaled passed through Caesar.
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| « Last Edit: Jul 23rd, 2009, 2:02pm by Benny » |
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Benny
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Re: various physics questions
« Reply #102 on: Jul 25th, 2009, 8:32am » |
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Lots of people have the habit of drinking half a cup of tea with milk and then replenishing with tea from the pot without adding more milk. If you drink 3/4 of each cup before topping off, only a 1/4 of the original milk content remains. So, after 10 top-ups the final milk concentration will be reduced by a factor of (1/4)10 = 1/1,048,576.
That's pretty strong tea.
A similar process of successive dilution is used in the preparation of homeopathic medecines.
A solution of the supposed therapeutic is diluted, typically with 99 parts of pure water or
alcohol to one part of the original solution.
The process doesn't stop there: the dilution is repeated, this time starting with the already diluted ingredient.
The process of successive is repeated up to 15 times before the final solution is administered to the patient.
A calculation similar to the one for working out the strength of your cup of tea gives the concentration of the homeopathic solution.
It's (1/100)15 = 1e - 30
But a 300 ml, about one full cup (1 US cup = 236.588237 ml), ...
More info here
... of the solution would contain a total of only about 1e25 molecules.
That means that the number of molecules of therapeutic ingredient in the cup would be just
1e25 X (1e - 30) = 1e - 5, or 1/100,000
It is not possible to have a fraction of a molecule: what this means is that there's a chance of only 1 in 100,000 that there will be one of those molecules in the cup of the solution you drink.
The proponents of homeopathic remedies get around this by suggesting that the water or alcohol
used in the dilution process "remembers" the earlier presence of the active ingredient.
Quite an extraordinary statement !!
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| « Last Edit: Jul 25th, 2009, 8:36am by Benny » |
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rmsgrey
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Re: various physics questions
« Reply #103 on: Jul 26th, 2009, 4:42am » |
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The real question is why the homeopathic water remembers the drug and not, say, all the times its been part of urine - or any impurities in the air or on the glassware used in the process...
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towr
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Re: various physics questions
« Reply #104 on: Jul 26th, 2009, 6:54am » |
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on Jul 26th, 2009, 4:42am, rmsgrey wrote:| The real question is why the homeopathic water remembers the drug and not, say, all the times its been part of urine - or any impurities in the air or on the glassware used in the process... |
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It's the concussing  Shaking vigorously after each dilution is absolutely essential. It's like magic.
Of course, magic doesn't work either, so ...
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Ronno
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Re: various physics questions
« Reply #105 on: Jul 26th, 2009, 8:28am » |
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Its also not up to just 15 times. I have seen vials of drugs of potency 10M and I know there exists CM. That is the dilution is done a 100000 times.
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Benny
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Re: various physics questions
« Reply #106 on: Sep 6th, 2009, 11:37pm » |
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I'm glad the website is up again.
Two Interesting Questions :
Here are two interesting questions you can ponder to exercise your brainpower. The first: If you push on the end of a broomstick or iron bar and move it, does the other end move at the same time? Now that may not seem too interesting at first glance, but it directly leads to the second: Can anything move faster than the speed of light? The answers to these could have profound consequences.
Don't worry if you didn't do well in your physics classes. Simple logic and a few facts will suffice for playing around with these concepts for now. We'll start with the fact that most physicists believe that nothing can move faster than the speed of light. That speed, by the way, is about 299,792,458 meters or 186,000 miles per second.
It certainly seems that if you were to push or pull one end of a long bar that the other end would move at the same time. But imagine an iron bar that is ten light years long, spanning the distance between here and another planet that has intelligent life. If you push or pull this end does the other end move at the same time? If so you could transmit information through a series of movements, using Morse code, for example. You could transmit several sentences in a matter of seconds or minutes, instead of the ten years it would take to do so using radio waves or light signals.
But this is contrary to the widely accepted view that nothing can move faster than the speed of light. Although the bar itself would move slowly, the information would be transmitted those billions of miles in just seconds - much faster than light or radio waves can travel (in fact, even the light of our own sun takes over eight minutes to get here). So can the other end of the bar move at the same time?
Obviously either our "common sense" idea that the whole bar would move at the same time is wrong (perhaps the motion is transmitted as a wave through the bar), or...
Continued here ... Two Interesting Questions
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towr
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Re: various physics questions
« Reply #107 on: Sep 7th, 2009, 12:24am » |
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Quote:| Now, when someone with more knowledge of physics tells me that nothing can move faster than the speed of light, I ask if something could (at least in theory) move at 60% of the speed of light. They universally answer yes. I then suggest that if a space ship were to pass over the Earth at 60% of the speed of light and another were to do the same in the opposite direction, that in relation to each other they would be going at 120% the speed of light - which is supposed to be impossible. |
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Except they have a different clock and ruler to measure by, and so observe a speed much less than lightspeed.
The observer from earth sees them going apart faster than the speed of light, but doesn't see either of them go faster than lightspeed. And neither do the observers on either rocket see anything or anyone going faster than the speed of light, because they see the universe in their own reference frame.
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rmsgrey
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Re: various physics questions
« Reply #108 on: Sep 7th, 2009, 5:03am » |
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Yeah, special relativity nails shut the coffin lid on the idea of rigid objects as anything other than a handy day-to-day approximation.
Though if you think a bit about the concept of a perfectly rigid object, and compare it to common objects that are "rigid enough" - they act like perfectly rigid objects under everyday conditions - it becomes clear that the idea of a perfectly rigid object is pretty non-physical in newtonian physics too...
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SMQ
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Re: various physics questions
« Reply #109 on: Sep 7th, 2009, 5:04am » |
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First, a minor nitpick: the speed of light (in free space) is, in fact, exactly 299,792,458 meters per second. Why? By definition! The modern meter is defined to be exactly 1/299,792,458 of the distance light travels through free space in one second.
The first question is an easy one: no, the ends don't move at the same time. When you push one end of the bar, the molecules of the bar that you push on push on the molecules next to them, which themselves push on the molecules next to them, and so on to the other end of the bar. This creates a compression wave which moves from your end of the bar to the other end until all the molecules are again the "preferred" distance from one another.
Not only does that compression wave not move faster than the speed of light, it moves much slower than that: the speed of sound in whatever material the bar is made of. For instance, the speed of sound in iron is around 5,120 m/s, so for a 10-light-year-long iron bar, the push would take around 586,000 years to move the other end!
If that seems ridiculous, remember just how massive such a bar would be, and how much force it would take to move it at all.
--SMQ
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towr
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Re: various physics questions
« Reply #110 on: Sep 7th, 2009, 5:16am » |
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on Sep 7th, 2009, 5:04am, SMQ wrote:| If that seems ridiculous, remember just how massive such a bar would be, and how much force it would take to move it at all. |
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Well, you don't have to move all of it, just tap it really hard to send the compression wave on its way (and hope it doesn't dampen out over the course of its travel). Only a small section has to be moving at any one time.
And actually, any amount of force will move it. And it will continue moving until an opposite force stops it 
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| « Last Edit: Sep 7th, 2009, 5:20am by towr » |
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Mickey1
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Re: various physics questions - Schrodinger's cat
« Reply #111 on: Feb 6th, 2010, 1:17am » |
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A cat in the park
Assume you detected a single particle through a slit using two detectors left and right perhaps equal in size - together blocking all possible particle directions.
I reality you would have to wait for one registration in very low intensity beam. The quesiton is which one was the next registration, right or left?
You could i) look at both detectors, ii) look at either one, or iii) take a stroll in the park. Alternativ iii) will give you the same situation as Scrodinger and his cat. If you want more drama you may attach a dramatic consequence system to one of the detectors.
I see I need to add this - lets call it Schrodinger's steake.
In both cases (schrodinger's cat and my cat in the park) we have models describing a known system and ii) an unknown future. There is nothing more to it than that. (Also, there is no justification for reading mind-dependence into Heisenberg's relation). You buy a lottery ticket and you check it a long time the drawing. You might have won or lost. Why built a model around that? Alternatively you are on your way home while another person has prepared dinner - what might it be, chicken or steake?
If you were pressed to build a model around the chicken/stake or dead/alive cat, Schrodinger method is right in principle, but there are not two realities, only two model states, not the same thing. About models vs reality see my notes on the site from Berkeley
http://goneri.nuc.berkeley.edu/pages2009/slides/Jensen_Comments%20to%20t he%20students.pdf
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| « Last Edit: Mar 11th, 2010, 4:27am by Mickey1 » |
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Mickey1
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Re: various physics questions
« Reply #112 on: Apr 22nd, 2013, 2:09am » |
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Perhaps I should add one more – less cynical - comment about the Schrödinger cat.
Let me first say that hardware, i.e. macroscopic objects, can be included in QM uncertainty. Schrödinger therefore does not attempt to introduce any counterargument to QM. He just shares a weird feeling.
The debate e.g. between Bohr and Einstein on the issues about the uncertainty principle in Solvay conference 1927, included uncertainty of the position of a box. Also Heisenberg says about a hypothetical investigation of particles in a microscope to determine location: “It immediately raises the question about the position of the microscope, and its position and momentum will also be found to be subject to [the uncertainty relations]”. (The physical principles of the quantum theory, Univ. of Chicago Press, 1930, p. 22). The theory just appears strange if we use “classical intuition”.
There are lots of these kind of paradoxes in QM. An even stranger aspect lies in the formulation of the principle itself: the concept uncertainty of e.g. a particle’s location assumes that it indeed possesses exact location and momentum – how else could we be uncertain of the particle's location if it never existed in the first place?
The counterposition is Laplace’s: a vast intelligent being “could embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.”
But let me get back to my point in this post, namely that the main requirement for a thought experiment is that it must follow the laws of physics. One can argue that Schrödinger’s cat placed in a closed room, and therefore hidden from us, does not qualify.
The cat might be heard through the door. We could imagine countermeasures to this, the room being increasingly well isolated but we can also, having access to an imaginary budget, take appropriate countermeasures using x-rays to see through the room. Nobel laureate Luis Alvarez studied the Second Pyramid of Chephren in Egypt using cosmic muon imaging to x-ray the pyramid in search for a hidden chamber. Using thought experiment techniques you might therefore always know what is going on. If you run out of muons, use neutrinos. Also, remember that a very high muon dose might kill the cat and destroy the premises of the experiment.
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Christine
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Re: various physics questions
« Reply #113 on: Sep 2nd, 2013, 9:57am » |
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When an eclipse of the Moon can be seen from the Earth, what can an observer on the Moon see/experience?
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Grimbal
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Re: various physics questions
« Reply #115 on: Sep 3rd, 2013, 9:38am » |
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You would experience the delight of being in a place where nobody has been before.
Or: choking to death if not properly dressed for the occasion.
OK, more seriously, from the Moon you would see the Sun pass behind the Earth, resulting in pitch black darkness.
Technically it could be called a sunset, since the Sun drops below the Earth horizon.
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| « Last Edit: Sep 3rd, 2013, 9:39am by Grimbal » |
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anglia
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Re: various physics questions
« Reply #116 on: Aug 20th, 2015, 9:55pm » |
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Sending a electric current around a loop of wire will give a certain magnetic field.
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