- #1
Punkanzee
- 5
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Hello Physics Forums, I am new here and I thank the community for any input I might receive on my physics paradox. To some of you this may not be a paradox and I hope that you may be able to explain to me how this makes sense from all reference points.
The paradox follows as such:
It has long been held that kinetic energy for objects is completely frame-dependent, that the energy content is relative to other observers. But for this I present a thought experiment, please excuse any miscalculations.
From our perspective on earth, Earth is stationary. In this thought experiment we have a rocket, rocket one, weighing 1,000,000 kg that is traveling in a straight line directly away from the Earth at 40,000 km/hour. The kinetic energy of this rocket given by the equation KE = 1/2MV^2 is 6.172 x 10^13 joules. Keep in mind the rocket is moving at 40,000 km/hour only when compared to an observer on earth. Traveling directly beside rocket one is rocket two that is traveling in the same direction as rocket one and is identical in mass, velocity, and kinetic energy. If rocket one is going to accelerate from 40,000 km/hour to 50,000 km/hour the amount of energy this would require is the difference in kinetic energy of rocket one moving 50,000 km/hour and 40,000 km/hour. The kinetic energy of a rocket one moving 50,000 km/hour is 9.645 x 10^14 joules. So the amount of energy in order to accelerate rocket one from 40,000 km/hour to 50,000 km/hour is 9.465 x 10^14 joules – 6.172 x 10^13 joules = 8.848 x 10^14 joules. As we can see the amount of energy required to accelerate the rocket is enormous compared to the initial kinetic energy of the rocket moving 40,000 km/hour. This is caused of course by the exponential factor in the equation for kinetic energy. However 50,000 km/hour from an observer on Earth is only 10,000 km/hour from an observer on rocket two since to begin with rocket one had a velocity of 0 km/hour because both rockets were moving beside one another at the same velocity. And because this is the case from rocket two's observation, only 3.858 x 10^12 joules of kinetic energy will be required from rocket two's perspective because rocket one is accelerating from 0 km/hour to 10,000 km/hour. So clearly kinetic energy depends on the perspective of the observer.
However, this doesn't make sense once you take into account amounts of energy that will stay universally constant regardless of observation point such as light. In order to take a deeper look into the problem two scenarios are presented. In both scenarios it is irrelevant how much energy both rockets required to accelerate from the Earth to their current velocity and position in space. Both rockets are powered by Variable Specific Impulse Magnetoplasma Rocket (VASIMR) thrusters because it is a highly efficient means of propulsion and requires no explosive chemicals. VASIMR is an is an electro-magnetic thruster that uses radio waves to ionize a propellant and magnetic fields to accelerate the resulting plasma to generate thrust. This system of propulsion is important because it can be powered electrically. In the next two scenarios microwaves will be emitted by either the Earth or rocket two and absorbed by rocket one and then converted into electricity and thus power the VASIMR to accelerate rocket one. In both scenarios the energy to produce the microwaves comes from fission nuclear reactions. For this thought experiment assume all transfers of energy are 100% efficient.
In scenario one microwaves will be emitted from the Earth only to rocket one in order to accelerate rocket one from 40,000 km/hour to 50,000 km/hour. The energy required in the form of microwaves can be calculated and would be equal to the energy calculated earlier to accelerate rocket one to 50,000 km/hour so we would need 8.848 x 10^14 joules of energy in the form of microwaves.
In scenario two, instead of the Earth emitting microwaves to rocket one, rocket two will be emitting microwaves to rocket one. As stated earlier from rocket two's perspective rocket one will be accelerated from 0 km/hour to 10,000 km/hour and will require 3.858 x 10^12 joules of energy. This amount of energy will be transferred between rockets also in the form of microwaves.
Take an alternate scenario, where the microwaves are transferred first from the Earth to rocket two. The microwaves are stored by rocket two in a battery of some sort and then transferred to rocket one. Now which energy is rocket two going to send to rocket one? The smaller amount which makes sense for rocket two or the larger amount that makes sense for earth?
Light energy is given by the equation: Planck's constant x frequency of the light. There is no such exponential factor and light energy remains constant regardless of where the observer is or how fast the observer is moving. The Doppler effect, responsible for red shift is not going to affect the overall energy if the Doppler effect can even be said to be making an impact in this thought experiment. Therein lies the paradox.
The paradox follows as such:
It has long been held that kinetic energy for objects is completely frame-dependent, that the energy content is relative to other observers. But for this I present a thought experiment, please excuse any miscalculations.
From our perspective on earth, Earth is stationary. In this thought experiment we have a rocket, rocket one, weighing 1,000,000 kg that is traveling in a straight line directly away from the Earth at 40,000 km/hour. The kinetic energy of this rocket given by the equation KE = 1/2MV^2 is 6.172 x 10^13 joules. Keep in mind the rocket is moving at 40,000 km/hour only when compared to an observer on earth. Traveling directly beside rocket one is rocket two that is traveling in the same direction as rocket one and is identical in mass, velocity, and kinetic energy. If rocket one is going to accelerate from 40,000 km/hour to 50,000 km/hour the amount of energy this would require is the difference in kinetic energy of rocket one moving 50,000 km/hour and 40,000 km/hour. The kinetic energy of a rocket one moving 50,000 km/hour is 9.645 x 10^14 joules. So the amount of energy in order to accelerate rocket one from 40,000 km/hour to 50,000 km/hour is 9.465 x 10^14 joules – 6.172 x 10^13 joules = 8.848 x 10^14 joules. As we can see the amount of energy required to accelerate the rocket is enormous compared to the initial kinetic energy of the rocket moving 40,000 km/hour. This is caused of course by the exponential factor in the equation for kinetic energy. However 50,000 km/hour from an observer on Earth is only 10,000 km/hour from an observer on rocket two since to begin with rocket one had a velocity of 0 km/hour because both rockets were moving beside one another at the same velocity. And because this is the case from rocket two's observation, only 3.858 x 10^12 joules of kinetic energy will be required from rocket two's perspective because rocket one is accelerating from 0 km/hour to 10,000 km/hour. So clearly kinetic energy depends on the perspective of the observer.
However, this doesn't make sense once you take into account amounts of energy that will stay universally constant regardless of observation point such as light. In order to take a deeper look into the problem two scenarios are presented. In both scenarios it is irrelevant how much energy both rockets required to accelerate from the Earth to their current velocity and position in space. Both rockets are powered by Variable Specific Impulse Magnetoplasma Rocket (VASIMR) thrusters because it is a highly efficient means of propulsion and requires no explosive chemicals. VASIMR is an is an electro-magnetic thruster that uses radio waves to ionize a propellant and magnetic fields to accelerate the resulting plasma to generate thrust. This system of propulsion is important because it can be powered electrically. In the next two scenarios microwaves will be emitted by either the Earth or rocket two and absorbed by rocket one and then converted into electricity and thus power the VASIMR to accelerate rocket one. In both scenarios the energy to produce the microwaves comes from fission nuclear reactions. For this thought experiment assume all transfers of energy are 100% efficient.
In scenario one microwaves will be emitted from the Earth only to rocket one in order to accelerate rocket one from 40,000 km/hour to 50,000 km/hour. The energy required in the form of microwaves can be calculated and would be equal to the energy calculated earlier to accelerate rocket one to 50,000 km/hour so we would need 8.848 x 10^14 joules of energy in the form of microwaves.
In scenario two, instead of the Earth emitting microwaves to rocket one, rocket two will be emitting microwaves to rocket one. As stated earlier from rocket two's perspective rocket one will be accelerated from 0 km/hour to 10,000 km/hour and will require 3.858 x 10^12 joules of energy. This amount of energy will be transferred between rockets also in the form of microwaves.
Take an alternate scenario, where the microwaves are transferred first from the Earth to rocket two. The microwaves are stored by rocket two in a battery of some sort and then transferred to rocket one. Now which energy is rocket two going to send to rocket one? The smaller amount which makes sense for rocket two or the larger amount that makes sense for earth?
Light energy is given by the equation: Planck's constant x frequency of the light. There is no such exponential factor and light energy remains constant regardless of where the observer is or how fast the observer is moving. The Doppler effect, responsible for red shift is not going to affect the overall energy if the Doppler effect can even be said to be making an impact in this thought experiment. Therein lies the paradox.