Naked Science Forum
On the Lighter Side => New Theories => Topic started by: sorincosofret on 14/05/2008 09:28:07
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Other lifts experiment and equivalence principle
Background and actual explanation
The equivalence principle: to an observer inside the elevator, without possibility to observe the external world, there is no physical experiment that it could be performed to differentiate between an gravitational field and an accelerated motion.
Working with light is quite difficult because its high speed. The original Einstein experiment can be performed, but requires a special attention and enough amount of money. In order to convince anyone about absurdities of actual general relativity, simple experiments, able to be interpreted even by unskilled people are developed.
First experiment
Two lifts one situated in gravitational field and another one in an acceleration field are considered like in fig. 2.9
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Figure2.9 Ball throwing in gravitational and accelerated field
On every lift a golf player having a device for ball throwing is considered.
In case of gravitational field when the device throws the ball with an angle α, the trajectory of ball is a known parabola. After the y axis the ball moves for a time upward and after that downwards related to the floor of lift considered as reference.
In second case, when the machine throws the ball with the same angle α, the trajectory of ball is always upwards. The observer having already an idea of the place where the ball must fall will observe the curios trajectory of ball. Without applying any mathematical formula he will deduce a simple and logical conclusion. There is a fundamental difference between a gravitational field and an acceleration field and is impossible to have an equivalence of them. It is possible in some cases to have the same effect in both cases, but theoretically an infinity of causes can produce the same effect.
second experiment
The same frame with two lifts is considered like in fig 2.10 but in every lift there is a hunter having a fire arm and there is a possibility to measure the impact energy of bullets.
In every case, for every lift, the hunter will measure this impact energy for a horizontal bullet (E1) and for a vertical bullet (E2).
After that, the observer from every lift, compare the impact energy of bullets thrown in vertical direction with the energy for a bullet thrown in horizontal direction.
In case of a gravitational field, there will be a significant difference between this energies and ΔE = E2 - E1 will be different of zero, due to the fact that gravitational field modify the kinetic energy of bullet with different amounts in up presented cases.
In case of accelerating field, the observer will measure the same impact energy in both cases, more precisely E1=E2.
In case of closed observer, the throwing a bullet in this field means a action of gravitation in a specific manner of moving bullets. In case of a accelerated field of force the energy in both cases (vertical and horizontal) is the same, only the trajectory of bullets is apparent modified by accelerated field.
Again there is impossible to make the assumption of equivalence between an accelerated field and a gravitational filed.
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Figure 12. Bullet energy in gravitational and accelerated field
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Your diagram with an 'accelerated field'. Do you mean that the lift is accelerating in the direction of the arrows? Because, if you do, the projectile will appear, to the person on board, to follow the same path as under a 'stationary lift resting on the Earth's surface. That is the principle of equivalence, n'est ce pas?
Could you define more precisely what your 'acceleration field' means?
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The acceleration field has the same signification like in original Einstein experiment, and for example you can suppose that field is produced by a engine. In the original experiment it is impossible to discern when an observer leave a object to fall in first case, and in second case. This is because in the first case the object fall due to gravitation and in the second case the lift is accelerated upward and the object practically remain stationary. But for the observer who also is accelerated upward it ,,seems" that also in second case there is a free fall of object. If instead of leaving of object to move toward floor, the observer throw the object upward, the entire situation is changed. Because in the first case the object is thrown against gravitation and in the second case in the same direction like acceleration field.
The experiments are discused only from the perspective of closed observer and not from the perspective of external observer. Only for a eyes closed observer and in certain condition there is a equivalence between an accelerated field and a gravitational field; for a external observer ...the equivalence is valid only in imagination.
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Einstein doesn't suggest an 'accelerated field' he just talks in terms of an accelerating frame; very different concepts, I think.
Your first diagram shows what an ground based observer will see - OK. But shows the paths of two different things - left picture shows the position of the ball, right picture shows the position of the lift; what are you comparing with what?
For an observer on board the lift, the trajectory of a thrown object will be the same in both cases.
I have an idea that, what you are having a problem with is the Kinetic Energy situation. Although KE is defined as ( m vsquared /2) the velocity is not absolute (relativity can only allow relative velocity).
The formula tells you the energy that an object could transfer if it, for instance, landed on the reference frame in which the velocity is measured. In fact, it assumes that there is a very large mass, stationary in that frame, so that you can actually transfer all the moving object's KE.
Treating the problem in Newtonian terms, a train hitting a 'stationary'fly at 100km/hr will transfer the same amount of energy as a fly hitting a 'stationary' train at 100km/hr.
In your scenario, the different answers you are getting for KE are due to the fact that you are trying to deal with absolute velocities rather than the relative velocities. If you consider the relative velocities, the KEs should be the same and equal to the energy that was put into the system in the first place.
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Dear Sophie,
My English is not so good so I will cite from an (English) book:
,,equivalence principle states that no experiment can distinguish the acceleration due to gravity from the inertial acceleration due to a change of velocity"
Of course, if you want to jiggle with therms I can put a simple question, too: If a pseudoforce has everytime real effects, can a real force to produce no effects?
In order to simplify the presentation, in up presented material, I didn't affirm nothing about referential's and how is observed the movement from different referential's.
So is better to define the lift referential(L) and let's say an external (P) referential.
In L referential, the observer is closed in the lift and without any window so for him it is impossible to detect its acceleration related to an external object.
What does it mean with the sentence:
For an observer on board the lift, the trajectory of a thrown object will be the same in both cases.
But you forgot to specify how is the form of trajectory in reality...and in your oppinion...
I suppose that in the first case (gravitational field) there are no problem with the form of trajectory, because is described in low level school manuals.
In the second case probably do you think the trajectory is the same like in first case?
What acceleration should produce in the second case a parabola form of trajectory?
Throwing the ball under an angle related to the floor, will produce an acceleration and the ball will move with this acceleration related to the floor. If the lift acceleration is constant and not variable, it is impossible for ball to fall again on the lift floor. It is really true that in case of a variable and growing acceleration, the floor will get closer to ball in time and the lift floor will hit the ball. Of coarse, a simple calculus will show the value of such variable acceleration. But even the lift floor will hit the ball, the trajectory of ball for internal observer will not be a parabola. So only looking at trajectory form an observer can decide if it's inside an accelerated field or gravitational field.
In low level celestial mechanic is presented the case when from a interstellar shuttle (far away from gravitational fields) a object id thrown away. That object will not fall again on the shuttle with a parabola trajectory as in your affirmation. For a shuttle passenger, that object is completely lost except the case when someone change the trajectory of shuttle in order to meet the object trajectory.
For an external observer P, it is necessary to establish the proper referential movement in order to analyse what is real and what is apparent from what he see.
If it's necessary please leave a message and I will make a detailed presentation.
The second experiment, related to bullet energy again (maybe due to may English), is wrong understood.
I don't speak about speeds and their character (even all are relative). I speak about impact energy measured let's say as depth of entering into a certain and convenient material layer
When a bullet is directed in vertical direction, the impact energy, measured let's say as the depth of passing through a certain material.
In case of an accelerated field the bullet will pass through a higher layer of material ( vertical shooting) then in case of a gravitational field. This is due to the fact that gravitational field take from kinetic energy of bullets during the trip between floor and ceiling.
In both cases the layer of material is hanged on the ceiling, and the observer has only the possibility to climb up and to check it.
Regards,
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I am sorry but I do not understand what you mean by an 'accelerated field'. This is crucial to my understanding of your ideas. Perhaps you could define it or give me a reference to it.
It was realised, long ago, that it is pointless to talk in terms of a Cartesian framework in space, with which you can measure 'absolute velocity'. It is relative speed which must be used if you want to discuss Kinetic Energy. Imagine two objects traveling extremely fast (referred to the Earth) but with only 1m/s difference in velocity. As far as one of them is concerned, the other one will have very low KE. A collision would do very little damage.
Whether or not your passenger could see out of his lift, he could tell how he was accelerating with a simple accelerometer (a mass on a spring). He would get the same result resting on the Earth or if he was far from Earth, accelerating in the direction of the roof, at 9.81m/s/s.
If he threw a stone whilst on Earth, it would follow a paraboloic trajectory within the lift because there would be acceleration (g) acting on the stone but the acceleration of the lift would be zero - the ground preventing it from falling to the centre of the Earth. Likewise, if he threw it in the same way in his accelerating lift, the trajectory would be indistinguishable from the first case. Once he let go of the stone it would not be accelerating any more (no force on it) but the floor of his lift WOULD be and it would catch up with the stone's constant speed path at the same time and place as if he threw it in the lift on Earth.
We must surely agree on these points? Otherwise discussion within the bounds of known Science can't be possible.
I suspect that your introduction of this 'acceleration / accelerated field' is the cause of confusion. But, hopefully, you will enlighten me.
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Dear Sophie,
I will leave the definition of acceleration/accelerated for a future discussion; for the up proposed experiment the presentation it's quite clear and measurements are more important.
You will smile but the foundation of mechanics (referring to referential definition) are not so firmly established.
Being already banned for advertising I can't tell more here; if you make a simple goggle search after my name you will see what are my preoccupations.
I will comment from your message:
Once he let go of the stone it would not be accelerating any more (no force on it) but the floor of his lift WOULD be and it would catch up with the stone's constant speed path at the same time and place as if he threw it in the lift on Earth.
It is really true that in case of a body moving in the direction of floor, for the closed observer, it is impossible to make a distinction between a gravitational field and an accelerated field.
But except this particular case, in other cases there is possible to make the distinction between them.
If you are not agree with me, please indicate me in the up presented experiment, for upward accelerated lift, what is the form of thrown ball for an inside observer and for an exterior observer. You can consider that first lift is suspended in a gravitational field with a long rope, and the second is accelerated upward with help of a rope.
I consider that physics must leave outside the literary and poetic language...as I see in your case; more problematic it will be with other physicists which spread a tons of mathematical formulas without any connection related to experiment.
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And do you have any experimental evidence (well documented, of course) to support your view, as you don't want Maths to be involved?
btw, an external observer of a ball thrown in your accelerating lift will see the ball travel in a straight line until it hits the sides because there is no impressed force on it whilst in flight.
Having seen a number of your posts on other sites I don't really think there is much point in pursuing this argument; you are clearly on an alternative (not Scientific) wavelength.
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Dear Sophie,
I have nothing against use of math in physics, with the distinction that math must be a tool of a physics and not a basement. Math deal with abstract concepts, physics deal with reality (or should deal with reality of phenomena).
The problem is more complicated because math is becoming a basement, and more than that, math is asked to create special concepts in order to be used by physics (see the operator concepts and their use in QM).
I've seen that you deliberately avoid to respond at a simple question:
How appear the experiment for a observer situated in the lift and every time you post how the movement is seen by external observer.
For you, as actual or future physicist, it's necessary to accept a principle of physics, regarding the equivalence of physics law for every observer and to leave to other readers to see on which part the balance hang and who is on the alternative or non alternative side of the problem.
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How appear the experiment for a observer situated in the lift and every time you post how the movement is seen by external observer.
That's an interesting comment, considering that, in an earlier post of yours, you actually quote a statement of mine which refers to an observer in a lift.
You seem to have argued in circles. What is it exactly that you believe Science has got wrong?
Perhaps you could bring yourself to define exactly what you mean by the 'acceleration field' of yours. Unless you do, there is little point in continuing with this thread.