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    Hi, I am currently studying GCSE physics but, as you can infer from my username, have a passion for particle physics, quantum mechanics ect.
    Whislt doing some further research, I thought of a question I cannot find the answer for. Here it is:

    If a Photon has a mass of zero, why is It affected by gravity. In terms of black holes etc.?
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    (Original post by Physics fanatic)
    Hi, I am currently studying GCSE physics but, as you can infer from my username, have a passion for particle physics, quantum mechanics ect.
    Whislt doing some further research, I thought of a question I cannot find the answer for. Here it is:

    If a Photon has a mass of zero, why is It affected by gravity. In terms of black holes etc.?
    Very good question, I think it's to do with kinetic energy and gravitational potential energy, there is a good video done by the IoP explaining about it. I'll try and and find it for you.
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    (Original post by Physics fanatic)
    Hi, I am currently studying GCSE physics but, as you can infer from my username, have a passion for particle physics, quantum mechanics ect.
    Whislt doing some further research, I thought of a question I cannot find the answer for. Here it is:

    If a Photon has a mass of zero, why is It affected by gravity. In terms of black holes etc.?
    Due to negs I looked into it a bit, I apologize it seems I was misinformed when I asked this same question to my physics teacher at the end of my GCSE's, I apologize :P OP, this might help a bit, and maybe lead you to further physics reading: http://math.ucr.edu/home/baez/physic...oton_mass.html
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    (Original post by Crimmy)
    a photon carries light energy, so it carries energy. E=mc^2, it carries energy so has a mass (m) due to Einsteins equation

    I also think its technically part of a group called the bosons, the force carrying fundimental particles. other ones (such as gluons) hold the quarks in atoms together and others do many more things, like tell 2 protons that theyre close together so must repel. I'm just quoting my physics teacher, and I dont fully understand it, so I'm afraid I cant help if this raises more questions then answers :P
    Thanks a lot! I think we have to consider Einstein's General relativity and the fact gravity is not a force in the ordinary sense of the word. Instead it Affects how distances are measured etc. Still, i am not entirely sure, unfortunately.
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    it carries energy so has a mass (m) due to Einsteins equation
    Nope. It carries energy as it has momentum. And the gravitational effect is because objects carry energy, not mass.
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    (Original post by Physics fanatic)
    Thanks a lot! I think we have to consider Einstein's General relativity and the fact gravity is not a force in the ordinary sense of the word. Instead it Affects how distances are measured etc. Still, i am not entirely sure, unfortunately.
    The guy above touched on the correct answer. Gravity does not only affect a force but any form of energy. And as was proved a hundred or so years ago, light bends due to gravity, imagine te good old fabric of space time example, the light beam will wobble and move according to that fabric. But the black hole has such a deep hole that the escape velocity to get out of that hole is bigger than the speed of light.
    Black holes are still a fascinating mystery.....

    Just to add, the definition about gravity affecting mass is Newtonian, Newtonian laws don't work everywhere. Sexy physics works around a black hole.
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    (Original post by Physics fanatic)
    Hi, I am currently studying GCSE physics but, as you can infer from my username, have a passion for particle physics, quantum mechanics ect.
    Whislt doing some further research, I thought of a question I cannot find the answer for. Here it is:

    If a Photon has a mass of zero, why is It affected by gravity. In terms of black holes etc.?
    Here's an excellent video addressing your question: http://www.youtube.com/watch?v=IM630Z8lho8
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    (Original post by Dima-Blackburn)
    Here's an excellent video addressing your question: http://www.youtube.com/watch?v=IM630Z8lho8
    Thanks. I will check this out.
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    Gravity in general relativity is not really a force, but rather a result of mass and energy bending spacetime. Particles, including photons, will travel along a geodesic (path of shortest distance in a curved space) which depends on how spacetime is curved, thus photon, though not carrying any mass, will bend under the presence of mass and/or energy.
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    This is due to the escape velocity. The escape velocity is the minimum speed required to escape a gravitational field.

    If you equate the kinetic energy and force of gravitation then you will get

    V^2 = 2Gm/r (m being mass of the planet, star, black hole etc)

    This shows that the mass of the object is irrelevant and this escape velocity will be the same for all things. Since a black hole is collapsed star, the mass is very large but the radius is a lot smaller. This means the escape velocity is greater than that of the speed of light. This is why light cannot escape.


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    (Original post by kalios)
    Nope. It carries energy as it has momentum. And the gravitational effect is because objects carry energy, not mass.
    I'll admit, I had to do some research of my own, but I knew some of the general direction of this question.


    A continuation from what Kalios put is this...

    E = mc^2 is not strictly true. Well, it kinda is... But it's not complete. The actual equation is:

    E^2 = m^2c^4 + \rho^2c^2


    You must be thinking, "how can something with no mass have momentum?". Well, it's equal to something called "the Planck constant" divided by its wavelength. The Planck constant is a very small number which deals with relating the energy of a photon with its respective frequency.


    Why is it affected by gravity? Well, the notion that mass is the only cause for gravity is Newtonian, and thus can't explain this. General Relativity is a better reason for why massless things are affected by gravity. I was always taught the example of those charity boxes where you put money in and it spins around and circles down into the bucket... Imagine the bucket is a really massive object and has deformed the space to create that dip. Photons might fall into that dip and bend towards the object with mass. The General Relativity approach discusses how distances in space are affected by gravity too.


    Probably not a perfect explanation, I'm afraid, but hopefully not a terrible one either.
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    Gravity is a manifestation of the bending of space-time and thus the fabric of reality. If you bend the path that light takes then it is going to follow that bent path.
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    (Original post by Physics fanatic)
    Hi, I am currently studying GCSE physics but, as you can infer from my username, have a passion for particle physics, quantum mechanics ect.
    Whislt doing some further research, I thought of a question I cannot find the answer for. Here it is:

    If a Photon has a mass of zero, why is It affected by gravity. In terms of black holes etc.?
    how is it zero i currently doing edexcel a2 and photon has a mass rite similarly so does a electron
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    (Original post by lopper)
    how is it zero i currently doing edexcel a2 and photon has a mass rite similarly so does a electron
    A photon is a wave. Although it can under go wave-partial duality. This means that a wave can experience properties of a particle and vice verca.


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