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rbj
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in HEP research and lit, is it common to think and write about the masses of the various leptons and quarks as relative to the invariant mass of some chosen standard particle? such as the electron? or something else?
Can you show where this is done? I don't remember seeing that.clem said:In pion interactions, it is convenient to take the pion mass =1, etc.
RightThe MeV is widely used, but is an arbitrary unit that depends on how the volt is defined.
?It would be more appropriate to set the proton mass=1, and that may eventually be used (if I am elected).
We can compare ratios, that's fine.Then we could compare our masses to those of alien civilizations.
The second has a completely arbitrary definition as multiples of a period of electromagnetic waves emitted in a transition in Cs-atoms. Meters are derived from that and the speed of light, indeed.QuantumPion said:Mass has no fundamental way of being defined, unlike time and distance which are defined by the speed of light.
I expect this to change in the next 2-3 years.The kilogram is defined as the weight of the international prototype kilogram (a platinum bar made to be about the same weight of 1 liter of water at room temperature).
mfb said:...
I expect this to change in the next 2-3 years.
OmCheeto said:Cool...
Do you think it will involve Carbon-12?
:tongue2:
Carbon-12 atoms could be used, but we are still looking for a volunteer to count them.OmCheeto said:Cool...Do you think it will involve Carbon-12?
Bill_K said:Carbon-12 atoms could be used, but we are still looking for a volunteer to count them.
Official Kilogram Losing Mass: Scientists Propose Redefining It As A Precise Number Of Carbon Atoms
Sep. 21, 2007
How much is a kilogram?
It turns out that nobody can say for sure, at least not in a way that won't change ever so slightly over time. The official kilogram -- a cylinder cast 118 years ago from platinum and iridium and known as the International Prototype Kilogram or "Le Gran K" -- has been losing mass, about 50 micrograms at last check. The change is occurring despite careful storage at a facility near Paris.
That's not so good for a standard the world depends on to define mass.
Now, two U.S. professors -- a physicist and mathematician -- say it's time to define the kilogram in a new and more elegant way that will be the same today, tomorrow and 118 years from now. They've launched a campaign aimed at redefining the kilogram as the mass of a very large -- but precisely-specified -- number of carbon-12 atoms.
At least two other proposals for redefining the kilogram are under discussion. They include replacing the platinum-iridium cylinder with a sphere of pure silicon atoms, and using a device known as the "watt balance" to define the kilogram using electromagnetic energy.
The kilogram is the last major standard defined by a physical artifact rather than a fundamental physical property. In 1983, for instance, the distance represented by a meter was redefined by how far light travels in 1/299,792,458 seconds -- replacing a metal stick with two marks on it.
"You could imagine having a lump of matter that actually had exactly the right number of atoms in it," Fox noted. "If you could build it by some kind of self-assembly process -- as opposed to building it atom-by-atom, which would take a few billion years -- you could have new kilogram artifact made of carbon.
Redefining the Kilogram
Scientists have crafted two new definitions for the common unit of mass. The fight to pick the best one is getting nasty.
Bob Grant | July 5, 2012
There's a secret war going on, and the future of science is at stake. The battle rages over the definition of "kilogram."
Defining the Planck kilogram is much trickier, requiring a working knowledge of quantum mechanics and special relativity, a massive and expensive piece of machinery, and considerable skill in mathematics.
That sounds like a weird description of the Watt balance project.Defining the Planck kilogram is much trickier, requiring a working knowledge of quantum mechanics and special relativity, a massive and expensive piece of machinery, and considerable skill in mathematics.
The purpose of normalizing particle masses against a natural standard is to provide a consistent and universal reference point for comparing the masses of different particles. This allows for more accurate and precise measurements in experiments and helps to establish a standard unit of measurement for particle masses.
A natural standard for particle masses is a reference point that is based on a naturally occurring phenomenon or property of particles. One example of a natural standard is the mass of a carbon-12 atom, which is defined as 12 atomic mass units (amu) and serves as the basis for the atomic mass unit scale.
Normalizing particle masses against a natural standard takes into account the inherent differences in the masses of different particles. For example, a particle may have a very small mass in kilograms, but when normalized against a natural standard, its mass may be a whole number or fraction of that standard, providing more meaningful and precise measurements.
No, different fields of science and different experiments may use different natural standards for normalizing particle masses. For example, in particle physics, the proton is often used as the natural standard, while in nuclear physics, the neutron is commonly used.
While it is possible to use non-natural standards for normalizing particle masses, it is not common practice. Natural standards provide a more consistent and universal reference point for comparisons, making them more reliable and accurate in scientific research.