The discussion revolves around the relationship between energy and mass at the origins of the universe, exploring whether energy existed before mass or vice versa. Participants engage with concepts from physics, including Einstein's equation E=mc², pair production, and the conservation of energy in particle collisions.
Participants express differing views on the relationship between energy and mass, with no consensus on whether one precedes the other. The discussion remains unresolved, with multiple competing perspectives presented.
Some participants highlight the limitations of the discussion, including the ambiguity of terms like "pure energy" and the complexities surrounding the definitions of mass and energy in different contexts.
You've never heard of pair production? Also, each proton-proton collision at the Large Hadron Collider produces many particles, each with mass that comes from the energies of the original protons.Pring said:rarely hear that people take mass from energy.
In the moving frame, mass is equivalent to its moving energy?Orodruin said:No, energy is not equivalent to mass. It would be more appropriate to call mass a type of energy, much like kinetic or potential energy. An object's mass is equivalent to its energy in its rest frame, i.e., its rest energy.
No. Please note that the concept of relativistic mass is essentially not used by physicists any more. See https://www.physicsforums.com/insights/what-is-relativistic-mass-and-why-it-is-not-used-much/Pring said:In the moving frame, mass is equivalent to its moving energy?
I can understand like that particles collisions produce energy, and the rest of them divide and transform to other particles.jtbell said:You've never heard of pair production? Also, each proton-proton collision at the Large Hadron Collider produces many particles, each with mass that comes from the energies of the original protons.
In what sense? The total energy after the collision always equals the total energy before the collision, where "energy" includes the "rest-energy" a.k.a. "mass" of each particle existing at a given time.Pring said:particles collisions produce energy
Pring said:the energy exist in advance of mass? Or mass exist in advance of energy?
I know energy must be conserved. Mass of each particle, which exists at a given time, changes into energy. It is not a good example of energy transforming into mass. Do pure energy directly change into particles?jtbell said:In what sense? The total energy after the collision always equals the total energy before the collision, where "energy" includes the "rest-energy" a.k.a. "mass" of each particle existing at a given time.
Thanks. I have read this passage, and really the concept of relativistic mass is less meaningful.Orodruin said:No. Please note that the concept of relativistic mass is essentially not used by physicists any more. See https://www.physicsforums.com/insights/what-is-relativistic-mass-and-why-it-is-not-used-much/
So first energy or mass?Vanadium 50 said:This is like asking if "left" exists before "up".
There is no such thing as "pure energy". Energy comes in many different form. Mass, or equivalently rest energy, is one such form.Pring said:Do pure energy directly change into particles?
Energy comes from material. Is there any experiment that the total rest mass increase after particles collisions?Orodruin said:There is no such thing as "pure energy". Energy comes in many different form. Mass, or equivalently rest energy, is one such form.
Can I understand the photon, which has no mass, as pure energy? If I just treat it as an assumption, it would take me any problems?Orodruin said:There is no such thing as "pure energy". Energy comes in many different form. Mass, or equivalently rest energy, is one such form.
No. Again, there is no such thing as "pure energy". Energy is not even a Lorentz invariant.Pring said:Can I understand the photon, which has no mass, as pure energy? If I just treat it as an assumption, it would take me any problems?
OK. Thanks, I have understood that nothing is called pure energy but rest energy, potential energy... In addition, is there any experiment that the total rest mass increase after particles collisions? This case means that rest energy change into mass. Finally, mass is equivalent to rest energy, which is inertial structure. Thus, once mass appears, the rest energy just appears. But I still have one question, in the very beginning of universe, which energy should exist firstly? Rest energy is the first one?Orodruin said:No. Again, there is no such thing as "pure energy". Energy is not even a Lorentz invariant.
If you are talking about adding up the individual rest masses before the collision and getting one figure, then adding up the individual rest masses after the collision and comparing then yes. That happens essentially every time particles are collided in an accelerator.Pring said:is there any experiment that the total rest mass increase after particles collisions?
Thanks. At the very beginning of universe, first energy or mass?jbriggs444 said:If you are talking about adding up the individual rest masses before the collision and getting one figure, then adding up the individual rest masses after the collision and comparing then yes. That happens essentially every time particles are collided in an accelerator.
You keep asking this question. Are you sure that it means what you think it means?Pring said:Thanks. At the very beginning of universe, first energy or mass?
Two photons going in opposite directions. Individually, neither has mass. Considered together they have mass. Which came first?Pring said:Thanks. At the very beginning of universe, first energy or mass?
Ibix said:Two photons going in opposite directions. Individually, neither has mass. Considered together they have mass. Which came first?
I don't think your question has an answer, any more than mine does. Mass and energy aren't entirely separate concepts, so talking about which one came first doesn't really make sense.
SiennaTheGr8 said:Mass and rest energy are the same thing, just expressed in different units. It might make things easier for you if you simply forget about "mass" altogether for a moment, and focus instead on energy:
The total energy ##E## of a closed system is a special quantity because it's conserved. That's why we care about it.
Now, a system's total energy is the sum of its rest energy ##E_0## and its kinetic energy ##E_k##:
##E = E_0 + E_k##.
You can see that when ##E_k = 0##, we have ##E = E_0##. So rest energy is just the total energy of a system as measured in its own rest frame.
Since mass and rest energy are fundamentally the same thing, your question can be rephrased: "Which came first: the total energy of a system, or the total energy of a system as measured in its rest frame?"
The question makes no sense.
Pring said:This case means that rest energy change into mass.
nitsuj said:how are two photons considered together as having mass?
Yeah, nothing different. Aha, I am so clumsy.Mister T said:Rest energy and mass are two different names for the same thing. Asking which came first or if one can change into the other are questions devoid of meaning. What difference do you think an answer would make?
So single photon is less massive. But from the perspective of multi-photon system, we select the rest frame, and the total energy is equivalent to mass. If we have a sphere symmetry system in a box, which always appears pairs of photons with opposite momentum in all directions by lasers, the equivalent mass could be arbitrarily large. Furthermore, if we move the box, it is hard.Mister T said:Consider some frame in which two photons have equal but opposite momenta. Such a frame is a rest frame for the two photon system, so the total energy of the two photons equals the mass of the system.
What seems strange is that the sum of the masses of the constituents of the system is not equal to the mass of the system. But this is the essential lesson of the Einstein mass-energy equivalence.
If I consider some frame in which two electrons have equal but opposite momenta. The total energy of the two electrons equals the mass of the system. So the system rest energy includes not only kinetic energy, but also their individual rest energy. Moreover, the potential is not considered for mass in any case. Finally, 'first energy or mass', the mass is equivalent to rest energy or system rest energy, and mass is just a perspective of rest frame. So energy always exists, and mass is just a perspective. Right?Mister T said:Consider some frame in which two photons have equal but opposite momenta. Such a frame is a rest frame for the two photon system, so the total energy of the two photons equals the mass of the system.
What seems strange is that the sum of the masses of the constituents of the system is not equal to the mass of the system. But this is the essential lesson of the Einstein mass-energy equivalence.
Pring said:So the system rest energy includes not only kinetic energy, but also their individual rest energy.
Pring said:Moreover, the potential is not considered for mass in any case.