Bharat Rakshak

Yes, point taken. But are the popularizers following the scientific sentiment. Smolin certainly makes it sound that way, that he is not alone and there is a real crisis within the scientific world and that many are working on different tangents to find the way forward. WRT string theory Smolin’s biggest criticism is not the galaxy sized accelerator as much as it is back ground dependent nature of the theory. I may be misrepresenting him but he says that space and time spring out of the gravitation field equations. And it always comes out as 3+1. This says something fundamental about the nature of relativity that it is back ground independent. According to him all of the more ’successful’ formulations of string theory, and apparently there are thousands, are all back ground dependent. Space-time is set manually and then string theory runs inside it. This is why the theory can be manually set to what ever data is discovered. It lacks predictive power.

Manual entry of parameters cannot be correct can it ? Smolins also focuses is on the parameters of the Standard Model. Something sets the mass of a proton or an electron and why that particular ratio. Or for that matter the mass of the Higgs Boson. The strength of the Strong Force or the Weak force, etc. Is there no real ferment within the physics world over the randomness of penciling in some numbers. Or have these already been explained. Smolin says otherwise and that string theory physics has come to accept these numbers a norml.

Smolins other big criticism of the new theories is for not predicting dark matter or dark energy. For that matter there is still no idea what these are and folks are resorting to Einsteins manually set cosmological constant.

The link has the full proposal for LIGO-India... a few hundred pages. The potential site is somewhere in Karnataka, must be in the dry flat regions for various reasons.
https://dcc.ligo.org/LIGO-T1200219/public

Theo, think about it. If a theory could predict everything, then there is very little to discover after that, no ? To get such a deep fundamental insight would be next to impossible. Even measurements or empiricism would not lead one to it. So it is always chipping away at the edges in a random walk manner so to speak. I would not classify the method as total madness or a bubble in the making, it is the ONLY process left for our human mind to understand what are the workings of the world we see.

What you are referring to is the hierarchy problem.

Right now I have one book on my desk called "The Computable Universe" with a forward by Sir Roger Penrose.
I quickly scanned some of the papers - some are good and some are so so. I am going through the forward itself. That is very interesting and touches upon several issues raised by the "Digital Universe" proponents (including Lee Smolin who has some theories about "the holographic principle", I guess). My understanding is that Penrose opposes the "digital universe" principle. Will have to read more and think over it and may be post here for your reading pleasure.

Yes, that is what Smolin says as well. Folks are stymied and left with playing small ball.

What he seems pi$$ed off about is the misrepresentation that string theory can explain everything. And this misrepresentation has lead to a powerful scientific consensus machine that has rewarded some folks while leaving others out in the cold.

I’m waiting for updates on the Dark matter experiment and the follow up on the AGASA, which potentially showed the very first Relativity violation. Though no scientist is taking it seriously yet. AUGER should confirm one way or another. It think the key will be finding a relativity violation. The you can begin attacking the problem from small peripheral areas as you say.
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Matrimc,

I would be interested to read your write up. IIRC Penrose has still not given up on proton decay.

so, does that mean that there is nothing called analog universe in that all communication at sub-atomic levels are digital enough?

In fact Penrose argues the other way. But things are a bit vague in my mind too. Right now working towards yet another deadline and another coming up pretty soon after that and here I am posting in BRF. I also have a few posts saved as drafts which I have to finish. But again some of the posters might have context switched.

Theo_Fidel wrote: As such another dead end. Another manually entered parameter.

Axiomatic and Self Contained System, I suppose.

You cant find anything beyond that unless you change your axioms but then they are not axioms anymore.

SriKumar wrote:

johneeG wrote:There is something known as “Free Expansion” or the “Joule-Thomson” effect, named after James Prescott Joule and J.J. Thompson two of the founders of the field of Physical Chemistry.
http://www.etomica.org/app/modules/site ... ound2.html
Free Expansion states that when a pressurized gas is exposed to a vacuum the gas expanding into the vacuum without any work being done. The gas is not “pulled” or “sucked” into the vacuum nor is it “pushed” out of the high-pressure container. In other words no work is done, no heat or energy is lost.

I looked at the weblink posted above. The reason the above theory does not fully apply is that the above example is that of a closed system.

If you look at the diagram, the gas is clearly expanding into a vacuum; but it is expanding into the _same_ container in which the gas is originally stored. There are indeed 2 compartments in the container, but it is one single overall container. Imagine what will happen to a molecule of gas that rushes out from one chamber into another...you had described it in nice detail earlier. It will move forward and then hit the wall of the second chamber ....which is clearly connected to the first chamber. The fact that it is connected to the first chamber makes all the difference. Imagine you are standing in a bus. It is similar to running and slamming into a wall inside a bus to make the bus move; or if you are sitting inside a bus and pushing on the seat in front to make it move. It is still Newtonian physics.

Saar,
in your example, bus moves because the bus is in contact with the road. There is a friction between road and bus tyres. So, the force applied from inside the bus is transferred to the road. So, the bus moves.

In vacuum, the spaceship is not in contact with any other outside item. So, newtonian physics does not apply.

Second, as soon as any opening is made in the chamber, the gas in the chamber will escape into the vacuum outside. This is called 'free expansion of gas'. A gas is not defined in vacuum. So, in vacuum gas does not exist.

Basically, it is not possible for the gas to be burnt because the gas will escape as soon as nozzle is opened in vacuum.

Amyrao wrote:Bio semi conductors experiments are at least three decades old.

Regarding the rocket efficiency why can't the divergent nozzle be with variable geometry like those of thrust vectoring like flexible to increase the divergent are to maximize the efficiency ?

About rocket efficiency:
Why are the rockets launched in a vertical position? I thought that if they are launched at an angle, the gravitational force on the rocket would be less, so the energy required to move the rocket against the gravitational force would be less...

Bade wrote:Theo, think about it. If a theory could predict everything, then there is very little to discover after that, no ? To get such a deep fundamental insight would be next to impossible. Even measurements or empiricism would not lead one to it. So it is always chipping away at the edges in a random walk manner so to speak. I would not classify the method as total madness or a bubble in the making, it is the ONLY process left for our human mind to understand what are the workings of the world we see.

What you are referring to is the hierarchy problem.

Saar,
the first thing to note is that what you are proposing is also a theory. You are proposing a theory that 'To get such a deep fundamental insight would be next to impossible. Even measurements or empiricism would not lead one to it. So it is always chipping away at the edges in a random walk manner so to speak.'

Thats your theory. It may or may not be true.

Anyway, within your theory, is it ever possible to reach a state(by 'randomly chipping away at edges') when one has understood the whole 'workings of the world we see'? I mean, according to your theory, at some stage, the society must reach a stage where they have learnt everything and have nothing more learn, right? Would you admit such a stage?

What happens once that stage is reached(regardless of how long it may take to reach that stage)? What next? At that stage, science would become dogma, right?!

Or would you say that it is impossible for people to ever reach that stage? If so, then your method would be a failure because it is unable to take one towards the stage of complete understanding.

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it is the ONLY process left for our human mind to understand what are the workings of the world we see.

The first and foremost thing for a human mind to understand is the human mind itself. Everything that is seen and understood is done through the prism of human mind. As long as the mind itself is not fully understood, all the other understandings(which are derivatives of the mind) are on a shaky ground.

People reach understanding of things in the following manner:
a) observation (Prathyaksha)
b) inference (anumaana)

You observe a phenomenon and then you make a inference(i.e. you propose a theory to explain the observation). The observation is supposed to be facts while the inference(or theory) is supposed to be an opinion. A theory(or opinion) that best explains the available facts(observations) is generally accepted. If a better theory, comes up, then that new theory will be accepted.

But, there are several problems in the above approach:
First and foremost, not all the facts are verifiable for everyone by observing. What I mean to say is that not everyone can observe and verify for themselves certain 'facts'. For example, not everyone can go to a space station and personally observe whether earth revolves around the sun or not. Or if the earth is circular or oval. ...etc.

In such cases, people have to depend on others' words. Words can be either heard or written. For example, most people obtain their knowledge by reading words in text-books, magazines, articles, papers, ...etc or they obtain their knowledge by listening to the words of 'experts'.

Word is called 'Shabdha' in Sanskruth.

People have to listen to the words of others and then, either accept them or reject them. Whether to accept someone's words or not, is again a subjective matter and not any objective matter.

Generally, what happens is if all people say the same thing, then it is accepted as the truth because there is no one challenging it or doubting. But, if there is a contrary view, then the controversy starts. When there are different views(on what are the facts), then which view to accept? That means the 'facts' themselves come under a scanner and are doubtful. This problem is frequently encountered in study of 'history'. When a record of history is taken, how does one know whether that record is truthful or not? Frankly, there is no way unless one can see into the past directly(i.e. make a direct observation). Any other method is only an approximation.

In 'science', people depend on 'experts' to get their facts. People believe that these 'experts' have personally observed(prathyaksha) and then arrived at their theories(anumaana).

Now, at a certain level, experiments are repeatable for laypeople and satisfy themselves. For example, there is gravity on earth. One can satisfy oneself by simply dropping any object and verifying it.

But, after a certain level, experiments are not repeatable for lay people. For example, gravity exists on moon. or gravity does not exist on moon. Now, unless one travels to moon and performs this experiment oneself, one cannot directly verify it.

In such cases, people would depend on those who claim to have done those things. So, their words have to be taken and believed. From this point on, there are 3 factors:
a) observation (prathyaksha)
b) words (shabdha) of others who claim to have observed
c) inference or theories (anumaana)

As I said, it is easy to believe others words, if there is only one viewpoint. But if there are multiple opposing viewpoints then, it becomes a question of which viewpoint one would like to believe.

For example, there are people who claim that they have seen God or Goddess. And similarly, there are people who claim that they have seen aliens or UFO. There are people who claim that they have gone to Moon and observed Earth. So on and so forth.

Now, from a neutral viewpoint, it is not possible for a person to verify any of the above claims. One is forced to simple accept or reject those claims. That means one is forced to place blind faith in the words of others. And generally people make decisions of whom to trust based on their biases. If a person is inclined to believe in Gods or Goddesses, then he may believe certain claims. If a person is a huge fan of modern day science, then they may believe aliens or UFO or landing on Moon ...etc. Basically, it comes down to the mentality of the person. What he likes and dislikes. What he wants to believe and not believe.

There is another point: people lie frequently.

People frequently lie. It happens all the time at all the places. Scientists, politicians, soldiers, doctors, lawyers, technicians, priests, ...etc all lie. And if people are forced to choose between lying and forgoing their jobs/perks/pleasures, then the lying will increase.

So, people are prone to lying and open to lying. Further, people are also prone to being fooled by others. All of us can fool others and be fooled by others.

Then, everyone has certain needs and weaknesses. And most important point is that there are powerful groups in the world who can control things by controlling the finances. So, which scientific experiment needs to be funded and which should not be funded is ultimately decided based on whether its useful or not to the person who is funding it.

And if these powerful people form into a cartel, then they can easily dictate what kind of 'facts' and theories are encouraged and which are discouraged. These cartels can be government bodies or private bodies or quasi-government bodies.

These bodies will make sure that no person can make claims of observations or inferences that run contrary to their interests.

And if they control the media, which frequently they do because the media also needs money to run, then they can also make sure which theories become popular among public and which are considered as 'superstitions' or 'loony'.

Basically we can divide science(including physics) into two categories:
a) verifiable for laymen by performing the experiments themselves. (Prathyaksha)
b) unverifiable for laymen and hence depend on others. (Shabdha)

In (b), physics is no different from any religion. One has to have faith in the words of high priests. Thats that.

In (a), one can make direct observation one self.
But, the point is 'beauty is in the eye of beholder'. That means what you see is based on your mind. What you think you observe is the interpretation of your mind.

Most of the times, mind makes many assumptions to fill in the blanks. It sees only partially and then makes certain fill in the blanks to optimize. So, one's mind itself is doing some internal chores which most of the time one is not aware of.

So, the basic question is:
when you observe an object, are you sure that that object actually exists in that manner only?
It is an accepted fact that certain circumstances can create tunnel vision.
Soldiers in battle generally have tunnel vision. So, their observations cannot be accepted completely because their vision is not proper. The problem is not with their eyes. The problem is with their minds.

Taking this further:
When you make an observation, are you sure that this object of your observation actually exists in the first place?
Because this is the fundamental question, right. Again, it is common experience that people observe objects that do not exist in physical realm. Such observations are made in dreams, hallucinations or delusions. But a critical thing to notice is that the person who is dreaming does not know that he is dreaming. Or the person who is hallucinating does not know that he is hallucinating. So, for them, the observation is as real as it gets.

So, one realizes that one is dreaming only when one has woken up. But that raises important point, then how do we know that when we make an observation, we are not dreaming or hallucinating or deluding? How do we know that the object that we see actually exists?

One simple way of verifying would be to ask others whether they can also see the object, right!

Here is a scenario:
You see a huge car hanging from the roof of a building. You ask a passerby whether he also sees the same, he says that he does. So, you assume its true. Then, you wake up from your dream and realize that both the car hanging from the roof and the passerby were part of the dream. So both of them were the creations of your own mind.

So, how can any one be sure that when one observes an object, the object exists?

Link

Link

Basically, at too higher(or lower) levels of physics, physics transforms into philosophy.

When people start equating physics with philosophy and slowly by extension with religion, I know we have a big problem. But then it is not my problem. It is up to the people who constructs such connections to clear their own cobwebs.

But then, it is not just the common man who confuses physics and philosophy, we should also blame those who said "God Doesn't play dice". In fact Physics is an endeavor to understand God particle anyway.

I don't know anyone who seriously expects that we will ever understand everything. This is the classic fish bowl problem. And we are stuck inside the fish bowl. The entire dark matter thing was only revealed recently due to oblique information that did not match up. We can only interpret what we can detect.

Right now I would settle for a single experiment that falsified Relativity however miniscule. Without that we truly are at an 'Axiomatic' dead end. The only saving grace is dark matter and dark energy. Which makes it clear we likely don't have a clue about the full universe. There was nothing 'God' about the 'God' particle. It was all a media creation. Privately a couple of professors thought that not discovering the particle would be many orders more important than discovering it.

We only learn when something does not match our expectations.
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BTW the 'God does not play dice' thing is understood poorly by regular folks.

You do understand the difference between long protracted philosophical arguments some like to make at the drop of hat in relation to mention of science vs an off the cuff quip like the one quoted above. It is not meant to mean "God" literally as many seem to understand or misunderstand.

Theo ji, I am aware of the fact the physicists don't like to call it God particle and there is nothing Godly about it. It is just an oblique reference in jest, but the whole physics started in understanding the creation of the universe and philosophy involved since early on.

Is it not true that Einstein's quote is in reference to his dislike for Heisenberg's uncertainty principle?

Yes I do. I didn't mean it that way either.

venug wrote:Is it not true that Einstein's quote is in reference to his dislike for Heisenberg's uncertainty principle?

AFAIK, it is much deeper than that. But then I am not qualified to talk about it as I am not a physicist.

Moved from Nukkad 71

Nandu and saip, my guess is way off the mark in that terminal velocity of a vertically fired bullet is lower than the one fired at a more flat trajectory. This seems to be due to tumbling (which leads to an increases air resistance, is that the case?). But my guess that the bullet still has enough velocity to cause harm bears out. Here is something from Wikipedia.

Bullets fired into the air usually fall back at terminal velocity, speeds much lower than those at which they leave the barrel of a firearm. Nevertheless, people can be injured, sometimes fatally, when bullets discharged into the air fall back down. Bullets fired other than exactly vertical are more dangerous, as the bullet maintains its angular ballistic trajectory, is far less likely to engage in tumbling motion, and so travels at a speed much higher than its terminal velocity would be in a purely vertical fall.

Here is a link which has more details - looks like things are more complicated than I first thought. Feels good to know the facts (or is it truth)) and erase little bit of my ignorance.

Can a bullet fired into the air kill someone when it comes down? April 14, 1995

Datum 3. Still, the question isn't how many people get injured or killed by falling bullets, it's whether such things are possible at all. On further investigation, it appears the 60 foot-pound injury threshold cited by Hatcher may be misleading — a falling bullet's kinetic energy (foot pounds) alone isn't a good predictor of the speed it needs to inflict a wound. B. N. Mattoo (Journal of Forensic Sciences, 1984) has proposed an equation relating mass and bullet diameter that seems to do a better job. Experiments on cadavers and such have shown, for example, that a .38 caliber revolver bullet will perforate the skin and lodge in the underlying tissue at 191 feet per second and that triple-ought buckshot will do so at 213 feet per second.

Mattoo's equation predicts that Hatcher's .30 caliber bullet, which has a small diameter in relation to its weight, will perforate the skin at only 124 feet per second. It's easy to believe such a bullet falling at 300 feet per second could kill you, especially if it struck you in the head.

Yes, I have seen this bullet thing on Mythbusters and they gave it Busted/Plausible/COnfirmed -- all three!

http://mythbustersresults.com/episode50

Also, another thing they tested was if a penny dropped from Empire State Building will have enough KE to kill someone on the ground (after all when you fire a bullet vertically -- 90 degrees -- it has to come to a stop and then start dropping) and they gave it 'busted' i.e it won't have enough KE

One reason is that the mass of a penny is (much?) lower than a bullet so KE(penny) < KE(bullet). The other possible factor is the difference in shapes - one is flat and the other is more rounded.

Does God play Dice? - Stephen Hawking

...Einstein was very unhappy about this apparent randomness in nature. His views were summed up in his famous phrase, 'God does not play dice'. He seemed to have felt that the uncertainty was only provisional: but that there was an underlying reality, in which particles would have well defined positions and speeds, and would evolve according to deterministic laws, in the spirit of Laplace. This reality might be known to God, but the quantum nature of light would prevent us seeing it, except through a glass darkly.
Einstein's view was what would now be called, a hidden variable theory. Hidden variable theories might seem to be the most obvious way to incorporate the Uncertainty Principle into physics. They form the basis of the mental picture of the universe, held by many scientists, and almost all philosophers of science. But these hidden variable theories are wrong. The British physicist, John Bell, who died recently, devised an experimental test that would distinguish hidden variable theories. When the experiment was carried out carefully, the results were inconsistent with hidden variables. Thus it seems that even God is bound by the Uncertainty Principle, and can not know both the position, and the speed, of a particle. So God does play dice with the universe. All the evidence points to him being an inveterate gambler, who throws the dice on every possible occasion.

To sum up, what I have been talking about, is whether the universe evolves in an arbitrary way, or whether it is deterministic. The classical view, put forward by Laplace, was that the future motion of particles was completely determined, if one knew their positions and speeds at one time. This view had to be modified, when Heisenberg put forward his Uncertainty Principle, which said that one could not know both the position, and the speed, accurately. However, it was still possible to predict one combination of position and speed. But even this limited predictability disappeared, when the effects of black holes were taken into account. The loss of particles and information down black holes meant that the particles that came out were random. One could calculate probabilities, but one could not make any definite predictions. Thus, the future of the universe is not completely determined by the laws of science, and its present state, as Laplace thought. God still has a few tricks up his sleeve.

saip wrote:Yes, I have seen this bullet thing on Mythbusters and they gave it Busted/Plausible/COnfirmed -- all three!

http://mythbustersresults.com/episode50

Also, another thing they tested was if a penny dropped from Empire State Building will have enough KE to kill someone on the ground (after all when you fire a bullet vertically -- 90 degrees -- it has to come to a stop and then start dropping) and they gave it 'busted' i.e it won't have enough KE

They should test it against a ball-bearing rather than a penny. Of course, the idea was if someone just tossed a coin would it hurt, but still the shape matters as it is not falling in vacuum.

Mathematically, terminal velocity—without considering buoyancy effects—is given by

where

V_t is terminal velocity,
m is the mass of the falling object,
g is the acceleration due to gravity,
C_d is the drag coefficient,
\rho is the density of the fluid through which the object is falling, and
A is the projected area of the object.

To get large K.E. decrease A and increase m.

Bade,

A has to be the cross-sectional area or some kind of average of the same, I suppose. Guessing again - if we stabilize a needle or cone or a ball-bearing such that the sharp end is always pointing in the gravitational force direction then we can increase m at a higher rate than the increase in A. One can always play with the material the dropped projectile is made with.

viv wrote:

saip wrote:Yes, I have seen this bullet thing on Mythbusters and they gave it Busted/Plausible/COnfirmed -- all three!

http://mythbustersresults.com/episode50

Also, another thing they tested was if a penny dropped from Empire State Building will have enough KE to kill someone on the ground (after all when you fire a bullet vertically -- 90 degrees -- it has to come to a stop and then start dropping) and they gave it 'busted' i.e it won't have enough KE

They should test it against a ball-bearing rather than a penny. Of course, the idea was if someone just tossed a coin would it hurt, but still the shape matters as it is not falling in vacuum.

While size and shape of penney is fixed a ball bearing could weigh several pounds and it would surely kill if dropped from Empire State building.

matrimc, you would need a infinitesimally small cross section, but at the same time a large mass to reduce the effect of drag. This leads to the necessity of a thin infinite wire to accommodate more mass. But then the even this will have a large surface area along the sides which will experience drag too. Only way to minimize the effects of the drag then, is to make sure it falls vertically down, otherwise the cross sectional area will change depending on tilt.

Anyway, the best is to make plots of Vt vs mass and A and look for surface minimum to get the smallest Vt possible to look for the opposite effect of least K.E. for safe bullets, so that abduls can fire in the air merrily without too much concern.

Bade wrote:When people start equating physics with philosophy and slowly by extension with religion, I know we have a big problem. ...

Here is a bhajan for god's particle, enjoy..

Bade wrote:matrimc, you would need a infinitesimally small cross section, but at the same time a large mass
...
Anyway, the best is to make plots of Vt vs mass and A and look for surface minimum to get the smallest Vt possible to look for the opposite effect of least K.E. for safe bullets, so that abduls can fire in the air merrily without too much concern.

Bade

It is not about whether the abduls can be safe. In fact we want just the opposite effect don't we ? MIRV petals opening and the "pennies" (not Baki rubees) - no without GPS - dropping on the abduls. How about venug chip in with his CFD and Theo with his mech modelling and shape optimization? fluid-structure interactions, hain jee?

Added later

Manufacturability and available materials (and their machinability) place constraints on the limiting case Bade has mentioned. The limiting case is an unconstrained problem but in real world (i.e. Newtonian Mechanics) there are no limiting cases. (well, probably I am speaking very loosely here).

So the only way out is a two step process - first model and simulate in silico to reduce the exponentially large design space and then validate using physical models and painstaking measurements. There would still be several local minima and one should be satisfied with finding at least a few. It is a long and hard road - nobody will give the tech on a platter to those who do not have it. No amount of philosophizing and praying in places of worship, building self-confidence, constructing complex political and economic theories would work either.

In Telugu there is a proverb "mantrAlaku chintakAyalu rAlavu" (Incessant Chanting of Mantras is not going to make the Tamarind Fruit fall from the tree).

The Lisa Randall interview actually adresses some of the "philosophical" questions regarding "full understanding" of the laws of physics. I got that from what AmberG posted above.

johneeG wrote:

SriKumar wrote:
http://www.etomica.org/app/modules/site ... ound2.html
Free Expansion states that when a pressurized gas is exposed to a vacuum the gas expanding into the vacuum without any work being done. The gas is not “pulled” or “sucked” into the vacuum nor is it “pushed” out of the high-pressure container. In other words no work is done, no heat or energy is lost.

Saar,
in your example, bus moves because the bus is in contact with the road. There is a friction between road and bus tyres. .....

Tires or no tires, the bus' final velocity will be unchanged (or zero, if the bus is stationary to start with). Assume that the bus is stationary to start with. When a person moves forward, the bus will move back a bit in response to the person pushing it backwards. The person accelerates forward, and the bus accelerates backwards in response (tires or no tires). When the person hits a front wall in the bus, it will stop the bus. The momentum of the bus and the person will balance out. But forget this example, it just confuses the matter.

Check the link you provided.

There is a clear reason the overall container will not move, even though the gas is escaping. The reason is that escaping gas molecules will not create an _unbalanced_ force (which is needed to make the chamber move). Because when the gas molecules come out with a certain velocity (and therefore momntum) they hit the wall of the _same_ container that they came out of. Check the diagram. There are 2 chambers but both chambers are in one container.

The example in your link is _not_ analogous to the original situation you are trying to prove (even though the gas is indeed escaping from a pressurized chamber into a vacuum chamber). It is not analogous because after release, the gas still sits inside the same container.

SaiK wrote:so, does that mean that there is nothing called analog universe in that all communication at sub-atomic levels are digital enough?

I think i got some examples.. voice. voice is natively digital. (64kbps)

SaiK wrote:

SaiK wrote:so, does that mean that there is nothing called analog universe in that all communication at sub-atomic levels are digital enough?

I think i got some examples.. voice. voice is natively digital. (64kbps)

I don't think this is quite correct. Sometime back we marveled at the double slit experiment. According to the double slit experiment a photon can be both quata or wave. A digital bit of 1 can interfere with itself meaning act in an analog manner. So photon can be both digital or analog and it is the observer who collapses the function. In essence this is the mystery of the world. How can something be both digital & analog at the same time. Yet experiment after experiment clearly shows that the universe indeed is built this way. While we can describe it mathematically the truth is we don't understand the foundations. We simply do not understand the base of quantum mechanics.

There was a famous german theorist on Discovery channel who said the question is inapplicable. It simply means we do not truly understand the nature of reality.
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Srikumar,

I don't know about work but potential energy has been converted to kinetic energy. So in space the box will definitely move.

One of the more odd results of Relativity is that pressure generates its own gravitation field. As does energy. Similar to matter.

Ok this will be easy for the science types but what the heck; Why do aircraft which have almost no tread on their tires (when compared to vehicles on road) don't slip as often on a very smooth tarmac (far smoother than road) on rainy days during landing ?

One of the more odd results of Relativity is that pressure generates its own gravitation field. As does energy. Similar to matter.

Could you please elaborate? Pressure? What exerts this pressure and what velocities are we talking here?

Not sure but doesn't pressure imply presence of a source of the force ? Which points towards existence of matter and hence mass > gravitational force ?

Photons do apply pressure on space craft sails for example, but these speeds are not relativistic enough to cause significant gravitational field. The spacecraft travels at a finite speed and also the photonic pressure is not significant.

But pressure also needs a surface for the force to have an effect...so not sure what Theo Ji was hinting at.

Venug garu, in freeman dyson's book "disturbing the universe" he envisages a space ship with solar sails. I do not remember the calculations now but what I remember is that such a space craft can achieve .1 C. We shoul be able to see relativistic effects at that speed I suppose.

matrimc garu, actually such spacecraft are designed. The sails are very huge to get an effective surface area when the photons hit the sails. So the concept is the spacecraft is maneuvered purely due to the forces these photons exert on the sails...but the draw back to such an idea is the velocities achieved by the spacecraft are not great, so you don't want such crafts where time is a factor. But are good for long space voyages where you want the spacecraft to sustain it's own flight. Another drawback is that the sails are susceptible to asteroid hits which can tear open or make the sail inoperable.

I am not a physicist myself. just throwing ideas to be crushed by gurus if they don't sound good perhaps. The sails are huge, the inertia is huge, I doubt such spacecrafts can actually achieve any significant velocities. I will stand corrected if I am wrong.

For a true exploration mission the requirements are far greater: when a NASA team in the 1970s, headed by Louis Friedman, suggested using a solar sail spacecraft for a rendezvous with Halley’s comet, they proposed a sail with a surface area of 600,000 square meters (6.5 million square feet). This is equivalent to a square of 800 meters (half-mile) by 800 meter – the size of 10 square blocks in New York City!

Even with such a gigantic surface, a solar sail spacecraft will accelerate very slowly when compared to a conventional rocket Under optimal conditions, a solar sail on an interplanetary mission would gain only 1 millimeter per second in speed every second it is pushed along by Solar radiation. The Mars Exploration Rovers, by comparison, accelerated by as much as 59 meters (192 feet) per second every second during their launch by conventional Delta II rockets. This acceleration is 59,000 times greater than that of a solar sail!

There seem to be really lively discussion here..!

So ...may be it is okay to bring some old unanswered (or at least with not too many different answers !)
questions from (Link here)

Let me repost it ..and add a few more (inspired by some of the discussion here):

>>>
Meanwhile, just for fun, few simple Physics problems..

1) If one sleeps under a tree, one will not get wet from morning dew. (or not as wet as if one sleeps under open sky)
Because the tree:
a) Absorbs star light
b) Keeps air from rising
c) Emits infrared radiation
d) Blocks the clouds
e) Tree is older than Chernobyl, hence it absorbed all radioactive Cs and produces heat
f) No, it is not true, you get almost as wet..

P2 A nuclear reactor cannot explode like a nuclear bomb because
a) It contains too much Uranium
b) It contains no uranium
c) Nuclear reactor depends on slow neutrons
d) It is carefully designed to shutdown quickly
e) None of the above, on average there is one explosion every year
f) Not e) but there were a few in Fukushima.

P3. Plutonium can explode with fewer generations than can Uranium because:
a) Plutonium fission releases more neutrons
b)Pu fission releases more energy
c)Pu does not require moderator
d)Pu turns into Uranium

P4 Wine sold in USA is legally required to be radioactive because
a) ....
b) Not true

P5 Professor Anwar Jamaal Kidwai (in the movie Ek Tha Tiger) walks a dog. The dog (weighing 52 pounds)
pulls on the leash, (pulling AJK), with a force of 200 N . According to Newton's third law, equal and opposite force of 200N is applied by the leash on the dog. In the movie we see that dog does move.This is is best explained by:

a) This is just a movie scene, in actual life dog will not be able to pull AJK as the forces cancel out.
b) The bus (shown in the background in the movie) is in contact with the road.
c) We need more than Newton's law, and have to consider odd results of Relativity, particularly, that pressure generates its own gravitation field pulling the dog in a geodesic trajectory of the curved space.
d) We have to consider Newton's first law, which is more relevant here than the third.
e) Write it in your own words.

(Actually, the above problem is based on a near identical problem I asked in a college freshman course)

P6. Speaking of falling bullets and pennies..Kinetic Energy of a typical penny size (about 2 gm) meteor is approximately equal to the energy of: (Hint: speed of a meteor hitting you may (or may not ) be same a falling bullet - why?)

a) 20 gms of TNT
b) 300 gms of TNT
c) 0.01 gm of TNT
d) 20 gms of gasoline
e) Your own calculation..

P7 I remember one hero in a Hindi movie (Angoor ?) boasted that he likes to eat "bandook ki goli" vs "vitamin ki goli" (bullet vs vitamin pill)..and have I see people calculating KE of bullet.. So here is a question .. for equal weight compare Energy in bullet (Kinetic energy here - fired at typical speed) hitting you with ghee (energy released to you when you eat).. (ghee = butter approximately)

Gram per gram ..


a) Energy in Bullet is 10 times ghee
b) Energy in Bullet is 100 times ghee
c) Energy in Bullet is 1000 times ghee
d)Energy in ghee is 10 times bullet
e)Energy in ghee is 100 times bullet
f)Energy in ghee is 1000 times bullet
e) Your own answer

venug, (I am dropping garu in the interest of brevity and typing - please assume and you may do so as well)

IIRC, what Dyson proposes is some kind of ground based (or is it lunar based which makes more sense) laser to keep the craft accelerating. Constructing it on moon would be a plus. Smaller gravity well to get out of (but you pay the price upfront to get all the infra or at least the bootstrap infra to moon in the first place). Once the ground laser station is established, a series of craft can be sent off at regular intervals. Asteriod hits are a real problem though. Certainly such a craft will be sluggish to maneuvre due to inertia. I don't remember Dyson discussing the details but an idea was put up. Somebody of his stature would have had some rough calculations (Fermi like) as for the feasibility of such an enterprise. But then again NASA might have refined it and found to be infeasible.

How do they slow down/maneuver. One of the problems of high velocity is energy required to maneuver is very high as well.