B Does Energy Have Mass and Other Beginner Physics Questions?

[tylerfarzam]

Can someone please answer a few questions I have? I am relatively (get it) new to physics and I just have a few questions. 1) Does energy have mass? It seems like energy does not have mass but i thought e=mc2 proved that it does. 2) Does gravity have an effect on energy? 3) If photons do not have mass, how are they affected by the curvature of space time? 4) If the curvature of space time can transmit information at the same speed as photons, is it possible that the electromagnetic force is the carrier of the gravitational force? 5) Is it possible to become an accomplished theoretical physics researcher if you do not have an actual research job? 6) What do researchers in general relativity study and do? Isn't relativity done and solved?

 

[Drakkith]

1) Does energy have mass?

Yes. For example, a hot block of iron has more mass than after it cools off.

2) Does gravity have an effect on energy?

Energy is not a physical object that can be acted upon. It is a quantity that things have, much like mass. You won't find energy off by itself somewhere. It is always something that objects or systems of objects have. As such, your question doesn't really apply to energy, but to more energetic objects. The hot block of iron mentioned above has more mass and thus gravitates more strongly than when it is cool.

3) If photons do not have mass, how are they affected by the curvature of space time?

They exist within spacetime and must follow certain rules. One of these is that their path through space can be changed due to the geometry if spacetime. You could also say that they have energy and therefore must obey gravitation.

4) If the curvature of space time can transmit information at the same speed as photons, is it possible that the electromagnetic force is the carrier of the gravitational force?

No. The two forces are very different when you dig into the details.

5) Is it possible to become an accomplished theoretical physics researcher if you do not have an actual research job?

Yes, but unlikely. When will you find time to do your research if you work a full time job unrelated to that research?

 

[jedishrfu]

1) mass is a concentrated form of energy https://www.quora.com/Does-energy-have-mass-or-light-as-in-light-beam-have-mass
2) yes with photons as an example.
3) photons have zero rest mass but have mass and can be deflected by a gravitational field
4) no, speed of light is a limit for any physical object to travel. However expansion of space time is not affected by this limit.
5) yes, see Gerard THooft’s website for how to become a theoretical physicist after many years of concentrated study.
6) they explore various natural phenomena using GR and QM in the hopes of discovering new things.

You can learn more about these things from Khan Academy or from the Open Star Physics book series:

https://openstax.org/details/books/university-physics-volume-1

 

[tylerfarzam]

1) mass is a concentrated form of energy https://www.quora.com/Does-energy-have-mass-or-light-as-in-light-beam-have-mass
2) yes with photons as an example.
3) photons have zero rest mass but have mass and can be deflected by a gravitational field
4) no, speed of light is a limit for any physical object to travel. However expansion of space time is not affected by this limit.
5) yes, see Gerard THooft’s website for how to become a theoretical physicist after many years of concentrated study.
6) they explore various natural phenomena using GR and QM in the hopes of discovering new things.

You can learn more about these things from Khan Academy or from the Open Star Physics book series:

https://openstax.org/details/books/university-physics-volume-1

Thankyou. But when I look him up I find a lot of different sites. Can you please give me a link to the one you are referring to.

 

[Ibix]

Does energy have mass? It seems like energy does not have mass but i thought e=mc2 proved that it does.

Energy can contribute to the mass of a system, but "energy has mass" would be an over-simplification. The relationship is $m^2c^4=E^2-p^2c^2$, where $p$ is the momentum of the object. Note that if $p=0$ this simplifies to Einstein's famous equation. However, for light, one can show that $E=pc$. So light has energy but zero mass.

Note that I'm using mass to mean the invariant mass (also known as the rest mass) as is standard in physics for the last few decades. A lot of popsci sources haven't caught up yet and still use mass to mean "relativistic mass", a now deprecated term for the quantity $E/c^2$. This is confusing, which is why the term isn't used much.

Does gravity have an effect on energy?

Energy isn't a thing floating round on its own. It's a property of a system.

If photons do not have mass, how are they affected by the curvature of space time?

The curvature of spacetime affects everything. That's kind of the point of modelling it that way. The status of massless things in Newtonian physics, where the force depends on the mass, is somewhat suspect. But relativity doesn't work that way.

If the curvature of space time can transmit information at the same speed as photons, is it possible that the electromagnetic force is the carrier of the gravitational force?

No. To the extent we know anything about a quantum theory of gravity, any force carriers it may have would be very different from photons. If they weren't, gravity and electromagnetism would be mathematically identical.

Is it possible to become an accomplished theoretical physics researcher if you do not have an actual research job?

Google Julian Barbour. I don't think it's an easy route.

What do researchers in general relativity study and do? Isn't relativity done and solved?

New applications (e.g. mdelling gravitational wave sources). Experimental tests (e.g. Gravity Probe B). Try to find a quantum theory of gravity that doesn't have singularities (e.g. Loop Quantum Gravity). Cosmology.

 

[Orodruin]

1) Does energy have mass? It seems like energy does not have mass but i thought e=mc2 proved that it does.

No. Mass and energy are properties of a system, not things of their own. It would be more appropriate to say that a system which has mass also has a corresponding amount of energy, given by $E = mc^2$.

2) Does gravity have an effect on energy?

Again, energy is not a thing but a property of a physical system. That said, gravitation (in general relativity) couples not only to mass but to all forms of energy, momentum, and stress. The reason Newtonian gravitation works so well for daily use is that, in all the settings that you will be familiar with, the amount of energy corresponding to the mass is much larger than any of the other sources of gravitation.

3) If photons do not have mass, how are they affected by the curvature of space time?

See (2). Gravitation does not couple to mass only.

4) If the curvature of space time can transmit information at the same speed as photons, is it possible that the electromagnetic force is the carrier of the gravitational force?

No. Electromagnetism and gravitation have properties that are very different. In relativity, any massless particle will travel at the speed of light.

5) Is it possible to become an accomplished theoretical physics researcher if you do not have an actual research job?

I would say no. Mainly due to the fact that you need a lot of time and you would have to make your living somehow, but also because you will find it hard to stay connected to the field and some resistance to getting your work published if you are not affiliated to a research institute (for better or worse).

6) What do researchers in general relativity study and do?

The obvious answer would be "general relativity". A more intricate answer would say that you can study the mathematical foundations, the implications, new ways to produce analytic solutions, ways of finding solutions numerically, ways in which gravity can be quantised, the relation to other fields. The list goes on.

Isn't relativity done and solved?

You cannot "solve" a physics theory. It does not work like that. You can always ask new questions about the theory and its implications that are worthwhile. The combined world knowledge about GR today is far beyond what it was in 1920. That being said, we do know a lot about how GR works and what its implications are. After all, we have studied it for more than 100 years.

 

[jedishrfu]

Gerard 't Hooft website:

http://www.goodtheorist.science/