This innocent sounding question requires some detailed consideration. Scientists distinguish between the words "weight" and "rest mass ". In ordinary life on earth, the two are the same . Rest mass or (more simply, mass) and weight are proportional to each other and the unit of measurement are so choose that they are the same. A weighting balance determine the weight; this is the force with which the earth attracts the object.
However, if the same object is in orbit around the earth, it is freely falling the towards the earth and is weightless. If you were that object and stood on a balance while both you and the balance were orbiting the earth the balance would show a reading of zero. Both the balance and you would be weightless, even though both would have the same mass as they had on the surface of the earth.
Therefore, I will assume that we are interested in finding out whether there is any entity in the universe that has zero "rest mass"?
The answer to that the last question is yes, and the very obvious "object", if you can call it that , is light .
We
Light photon have energy but zero rest mass. In addition, there are other particles called neutrinos that have zero or near zero rest mass. The existence of neutrinos was theoretically postulated to explain certain observations , and experimental evidence has since been gathered for their existence. There is some recent evidence that the neutrino mass may not be exactly zero, but they are very close to being mass-less.
Mass-less particles have an initial role in the universe. This is obvious as far as light and heat are concerned . It has been found that neutrinos are also central in determining the nature and evolution of the universe.
However, if the same object is in orbit around the earth, it is freely falling the towards the earth and is weightless. If you were that object and stood on a balance while both you and the balance were orbiting the earth the balance would show a reading of zero. Both the balance and you would be weightless, even though both would have the same mass as they had on the surface of the earth.
Therefore, I will assume that we are interested in finding out whether there is any entity in the universe that has zero "rest mass"?
The answer to that the last question is yes, and the very obvious "object", if you can call it that , is light .
Light photon have energy but zero rest mass. In addition, there are other particles called neutrinos that have zero or near zero rest mass. The existence of neutrinos was theoretically postulated to explain certain observations , and experimental evidence has since been gathered for their existence. There is some recent evidence that the neutrino mass may not be exactly zero, but they are very close to being mass-less.
Mass-less particles have an initial role in the universe. This is obvious as far as light and heat are concerned . It has been found that neutrinos are also central in determining the nature and evolution of the universe.
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