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11 votes

Is a photon truly massless?

Although everyone has heard of the famous equation: $$ E = mc^2 \tag{1} $$ few realise that this is a special case and applies only in limited circumstances. Specifically it applies only to a massive ...
John Rennie's user avatar
10 votes
Accepted

Can a big mass defect make the mass negative?

If you apply no rules to the possible interactions then what you describe is possible. But the negative bound state mass can be avoided if we assume two things: A force field that has always positive ...
Jos Bergervoet's user avatar
9 votes

Does life erode Earth's mass over time?

Remember that nearly all of life's energy ultimately comes from the sun. Life uses energy that is received from the sun, "mixes" it with matter from the earth, and eventually that energy ...
hdhondt's user avatar
  • 11.1k
9 votes

Is a photon truly massless?

The correct version of your syllogism is: $E=mc^2$ for a particle at rest. For a photon, $E>0$. For a photon, $m=0$. The correct conclusion is that a photon can never be at rest.
WillO's user avatar
  • 15.9k
6 votes

Can a big mass defect make the mass negative?

TL;DR: No, quantum field theory does not allow this. The general situation you describe is not at all exotic, and in fact this is why we have (meta)stable bound states. What you have termed 'mass-...
SethK's user avatar
  • 589
6 votes

Is a photon truly massless?

Light has inertia: it takes a force to change the direction in which they travel, and if you have a box with light bouncing around inside of it, it takes more force to change the speed of the box than ...
g s's user avatar
  • 14k
5 votes
Accepted

Why the Sun has a higher temperature than humans?

The thermal energy per gram of matter of the Sun is definitely higher than of humans, being between 6000K and 15000000K depending on where in the Sun. What you are probably thinking of is the fact ...
CPlus's user avatar
  • 1,009
5 votes

Is a photon truly massless?

I like pictures, and the relevant picture is: You can ignore the formulae, they are just high school trig, tho, so nothing prohibitive. (The do look bad, though, I think it's because they are crammed ...
JEB's user avatar
  • 35.3k
4 votes

Does life erode Earth's mass over time?

Good question! No, life does not reduce the mass of Earth. Life is cycling elements such as C, O, N and H. It is fuelled nearly completely by solar energy. This is converted to heat, which at the end ...
my2cts's user avatar
  • 25.3k
4 votes
Accepted

Why is the mass-energy graph for atomic mass $A=98$ not quadratic?

Who told you this would be a quadratic? The famous binding energy expression from the semi-empirical mass formula includes five terms. The volume and surface terms are constant in $Z$. The Coulomb and ...
anon's user avatar
  • 1,220
2 votes
Accepted

Why does the mass-energy equivalence apply to binding energy when it is derived purely through kinematic means?

I understand that by defining the four velocity, multiplying it by the rest mass and taking the entire thing's norm we get E2=m2+p2 This is not always an accurate description of the process. For some ...
Dale's user avatar
  • 103k
1 vote

Can a big mass defect make the mass negative?

This question leads to deep insights into what constitutes a particle relative to the vacuum. If you were to have a system of particles with binding energy less than the vacuum, the universe would ...
Xerxes's user avatar
  • 973
1 vote
Accepted

"Mass Shell" Condition on Euclidean Scalar Field

Yes, OP is right: In Euclidean (E) signature, the mass-shell condition is $-E_E^2=E^2_M={\bf p}^2+m^2$, and we're solving an elliptic boundary value problem, which is different from the hyperbolic ...
Qmechanic's user avatar
  • 206k

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