Paritosh Sontake Posted September 8, 2017 Share Posted September 8, 2017 As students, we have been taught that "mass can neither be created nor destroyed". So, how did the universe form? What I mean is if Law of conservation of mass is applicable, Then there is no way for the Planets, Stars, Nebulae, etc. to be created. Please Explain.... Link to comment Share on other sites More sharing options...
Strange Posted September 8, 2017 Share Posted September 8, 2017 3 hours ago, Paritosh Sontake said: As students, we have been taught that "mass can neither be created nor destroyed". This is not strictly accurate. Mass can be converted to energy, and vice versa. 3 hours ago, Paritosh Sontake said: So, how did the universe form? What I mean is if Law of conservation of mass is applicable, Then there is no way for the Planets, Stars, Nebulae, etc. to be created. Please Explain.... The matter and energy in the universe has always been present (as far as we know). It started out in a hot and very dense state, then expanded and cooled. That allowed parts of the cloud of gas to collapse to form stars. Eventually, some of the these stars died creating the heavier elements that Mae up planets, etc. 1 Link to comment Share on other sites More sharing options...
Sensei Posted September 8, 2017 Share Posted September 8, 2017 (edited) Process in which high energy photons are converted to matter-antimatter particles is called pair production. https://en.wikipedia.org/wiki/Pair_production Opposite process in which matter-antimatter particles are converted to photons is called annihilation. https://en.wikipedia.org/wiki/Annihilation Edited September 8, 2017 by Sensei Link to comment Share on other sites More sharing options...
studiot Posted September 8, 2017 Share Posted September 8, 2017 5 hours ago, Paritosh Sontake said: As students, we have been taught that "mass can neither be created nor destroyed". So, how did the universe form? What I mean is if Law of conservation of mass is applicable, Then there is no way for the Planets, Stars, Nebulae, etc. to be created. Please Explain.... Classical Physics (and other Science such as Chemistry) does not explain or treat creation or annihilation. Classical Science is concerned with finite term interactions or process and the statements you embolden refer to these. Questions involving infinite time space or matter are left unresolved, apart from potential theory. Some forms of creation/ annihilation and some aspects of infinity are treated by what is called Modern Physics. Within the context of classical Science five types of system are distinguished, open, closed isolated and quasi. An open system allows both mass and energy to enter or leave the system during the process. A closed system allows energy, but not mass to enter or leave the system during the process.* An isolated system allows neither mass nor energy to enter or leave the system during the process. An quasi system allows either mass or energy to enter and leave the system during the process, with the proviso that the amounts entering must equal the amounts leaving. * Can you see why we can't have a system that allows mass but not energy to enter or leave a system? Link to comment Share on other sites More sharing options...
Sriman Dutta Posted September 9, 2017 Share Posted September 9, 2017 Law of conservation of mass only applies to a closed system where there is no conversion of mass to energy. In case some energy comes into account, we have to consider energy and mass together, because E=mc^2. Link to comment Share on other sites More sharing options...
Paritosh Sontake Posted September 10, 2017 Author Share Posted September 10, 2017 Thank you all. This really solved my doubts..... Link to comment Share on other sites More sharing options...
studiot Posted September 10, 2017 Share Posted September 10, 2017 15 hours ago, Sriman Dutta said: Law of conservation of mass only applies to a closed system where there is no conversion of mass to energy. In case some energy comes into account, we have to consider energy and mass together, because E=mc^2. Classically the the conservation laws (both mass and energy) apply to open, closed and isolated systems, but differently applied. Much of Engineering Science deals with open systems and incorporates a discipline known as Transport Phenomena, which is particularly about applying the conservation laws in open systems. A simplified soundbyte version is Input = Output + Accumulation. Examples of systems would be A refrigeration system is a closed system, refrigerant mass is conserved but energy enters and leaves the system. A working fermentation vessel that is neither heated nor cooled is an example of an isolated system. A hydroelectricity plant is an example of an open system. Both mass an energy enter and leave the system. As regards the Universe and Cosmology, we simply don't know enough to confidently apply these tightly specified Classical laws. Modern Physics only offers tnetative hypotheses that are constantly being revised in the light of new information. We don't even know enough to confirm if the Universe is open, closed or isolated. Link to comment Share on other sites More sharing options...
Mordred Posted September 10, 2017 Share Posted September 10, 2017 True however the FLRW metric treats the universe as an adiabatic and isentropic fluid. Which is in essence closed as adiabatic is no net inflow or outflow Link to comment Share on other sites More sharing options...
studiot Posted September 10, 2017 Share Posted September 10, 2017 On 08/09/2017 at 10:06 AM, studiot said: A closed system allows energy, but not mass to enter or leave the system during the process.* * Can you see why we can't have a system that allows mass but not energy to enter or leave a system? Still no answer to this important question. Link to comment Share on other sites More sharing options...
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