What is the Lightest particle that is known so far?
341898
The tachyon has the smallest mass and is the only particle than can go faster than the speed of light
1054743
A major research institution has recently announced the discovery of the heaviest element yet known to science. This new element has been tentatively named "Administratium." Administratium has 1 neutron, 12 assistant neutrons, 75 deputy neutrons, and 111 assistant deputy neutrons, giving it an atomic mass of 312.\n\nLightest would be Hydrogen.\n\nelements consist of atoms which have protons, neutrons and electrons.
300067
A photon, which is a quanta of evergy below which you cannot go-this is the smallest, and only, particle which carries radiant energy.  The photon is the energetic equivalent of the quark in matter.
23843
Nope, everyone has it wrong.  There is a secret and even though we know it, we still cannot find the answer.  The questions is, "What is light."  Nobody knows what light is.  There are many theories, but none can be verified.  If we knew the answer to this question, there would be literally no limit to what could be known and done.  At one time we had no idea what electricity was, but, once we found out it's priciples and properties, look what was done with appliances and computers.  No, apply similar advances if we knew the principles of light.  A trip to Alpha Centauri (the closest star) would take shorter time to reach than Mars does now.
184804
Two things that I recall:  the detection of the Z0 boson (a bottom quark bound to a bottom antiquark; bottom quarks conserve a mathematical thing called 'beauty'; when CERN announced this, the headlines read, "CERN physicists detect naked beauty."  Sigh, probably the only article about particle physics some folks read...); and the measurement of the mass of the tau particle.\n\nNo doubt others, but I recall those two
272627
Pure Hydrogen, if by "lightest" you mean the gas with the lowest molecular weight.
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Light IS energy...sorry I can only think of one...:(
801276
Light is a particle. Wave is its function.
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Its not just for a microscopic particle. Its for any particle. The effect is only large for very small particles though.\n\nThink of it this way.\n\nIf you want to know precisely where a particle is you will have to use a very short wavelength of light to measure its position - you cannot be more accurate than the wavelength of the light. But very short wavelength light carries a lot of momentum. Each photon has momentum h/wavelength (h is Planks constant) - the shorter the wavelength the greater the momentum.\n\nBut if you hit the particle with a photon with a lot of momentum, it will accelerate it. As a result you will not be able to get an accurate measurement for its momentum. To measure its momentum accurately you would have to use a very long wavelength photon.\n\nThese are competing requirements.\n\nThe Hesienberg relationship quantifies these competing requirements by saying that the error in position multiplied by the error in momentum cannot be lower than hbar (Planks constant over 2 pi).\n\nPlanks constant is very tiny - around 6.62 e-34 Js. So it only matter for tiny particles.
12855
The electron has smaller mass than any of the known quarks, and of course smaller than the proton or neutron.  Search the rest mass of up and down quarks against the .5 MeV of the electron.  You'll get estimates on the order of several hundred MeV.  I've taken "Smaller" here to mean mass, since the standard theory of particle physics assumes electrons and quarks to be pointlike and therefore both have no volume.
194230
Between the electron and photon, photons will be smaller and lighter. But to counter it, there are actually even smaller things called quarks found in the electron and proton. These are REALLY small and each electron contains THREE of them, so u can imagine how small there are.
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light\nquarks are quarks
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Suprise answer and correct! PLASMA\nPlasma is also the most common form of matter in the universe!
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Except for photons, neutrinos are the smallest particles. The reason I say "except for photons" is that under current theory, photons have no mass at all (though they do have momentum).  They have some characteristics of particles, but I don't think you are asking about that kind of particle.\n\nUntil just recently, neutrinos were thought to have no mass as well, but a number of laboratories have demonstrated that it indeed has mass, but it is, as yet, too low to measure. Thus, under even the most strict definition, a neutrino is a particle.\n\n*edit* String theory is still very controversial and not accepted by consensus.
199003
a proton has a weight of approximately 1836.15 electrons
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http://math.ucr.edu/home/baez/physics/Relativity/SR/light_mass.html
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Particle and Wave.\n\nGood Luck\n\nJimmy