Re:The EmDrive just won't die
by PeterisP on Sunday September 13, 2020 @04:31PM
(#24463749)
As to your first question, distant gravitational fields can be ignored as per theory of relativity - if you're looking at an experiment in a black box (e.g. in an EmDrive) then an otherwise closed system in freefall in gravitational field is absolutely indistinguishable from a system at rest without that field, any experiment would give exactly the same results.
And for the second question, mass is energy and energy is mass (as per relativity). Adding or removing energy from a system makes it respectively heavier or lighter; if you heat up an object so that afterwards it has exactly the same atoms but just more internal energy, then it will be slightly heavier than when it was cold - the difference is very small (m=E/c^2, and c^2 is large) but nonzero.
If you're looking from outside at the behavior of an isolated black box, it's impossible to detect if inside it some mass is "lost" in a nuclear reaction i.e. converted to energy, as both the inertial and gravitational mass of a system is equivalent to the sum of both rest mass and energy, and that total is conserved. If that box pushes out energy/mass to outside or gains energy/mass from outside, then of course it is not a closed system. But converting rest mass to energy and vice versa in a chemical or nuclear reaction would not make it a non-closed system as long as all the inputs and outputs stay in the system, as the total gravitational effect of the system before and after the reaction would be exactly the same.
And for the second question, mass is energy and energy is mass (as per relativity). Adding or removing energy from a system makes it respectively heavier or lighter; if you heat up an object so that afterwards it has exactly the same atoms but just more internal energy, then it will be slightly heavier than when it was cold - the difference is very small (m=E/c^2, and c^2 is large) but nonzero.
If you're looking from outside at the behavior of an isolated black box, it's impossible to detect if inside it some mass is "lost" in a nuclear reaction i.e. converted to energy, as both the inertial and gravitational mass of a system is equivalent to the sum of both rest mass and energy, and that total is conserved. If that box pushes out energy/mass to outside or gains energy/mass from outside, then of course it is not a closed system. But converting rest mass to energy and vice versa in a chemical or nuclear reaction would not make it a non-closed system as long as all the inputs and outputs stay in the system, as the total gravitational effect of the system before and after the reaction would be exactly the same.