The discussion revolves around the relationship between mass and gravity, particularly questioning whether mass exists in the absence of gravity and exploring the implications of massless particles, such as photons, in the context of general relativity and quantum mechanics. The scope includes theoretical considerations, conceptual clarifications, and speculative connections to string theory.
Participants express differing views on the relationship between mass and gravity, with no consensus reached on whether mass can exist without gravity or how massless particles interact with gravitational fields. The discussion remains unresolved with multiple competing perspectives.
Some claims about the nature of mass and its relationship to energy and gravity are contingent on specific interpretations of general relativity and quantum mechanics, which may not be universally accepted. The discussion also touches on unresolved questions regarding the definitions and equivalences of different types of mass.
The latter.jines said:Thank you, jtbell. For purposes of clarification, would these two anti-parallel light beams (i.e, photons which are massless) be traveling on a "flat space-time", and they attract each other (Newtonian), or would these light beams be traveling on a curved spacetime, and this curvature is due to their presence (general relativity)?
PAllen said:The latter.
Well, per SR, two oppositely directed beams of light have positive invariant mass, while two beams in the same direction have zero invariant mass. This is just suggestive for GR, where the SET is EFE source term, but in this case it corresponds with what is known directly from the EFE (oppositely directed beams attract, parallel beams to not attract each other). Note that a single light beam exerts attraction on test body near it, though the effect is too small to ever likely be detectable (though it is directly calculable).DrStupid said:In that case there actually is mass.
jines said:I read somewhere that in the quantum world, inertial mass and gravitational mass are not the same.
If mass is equivalent to energy, then even a light beam (photon particles) would have some mass, right?
I thought that mass is just condensed energy. The bigger the condensed energy (i.e. more massive) the greater the gravitational force or the spacetime curvature. The lesser the condensed energy (i.e. particles) the more negligible the gravity. Is this too simplistic?
Relating it to string theory, does the frequency of vibration of each string (of energy) determine the type of particle and the energy density (i.e., mass) of a particle?