Gravity does not bend space time. According to our current theories, what we call gravity doesn't exist. We just see these things because matter bends space time, and that bending is what we simply call "gravity" as a fictional force. The real effect is that matter bends space time. The analogy is that if you're in a moving car, and you suddenly make a turn you feel a "force" that throws you outward. That force doesn't really exist, it's just because your body wants to keep going straight while the car is forcing it to turn in a circle. Likewise, the "force" of gravity does not exist. We only observe it due to our frame of reference. if you want to create a 1g well, then you need to use E = mc2 to find the mass you want, use E photon = h*f where h is Planck's constant, f is the frequency of light, E = n * E photon, where n is the number of photons.
Then you use basically Newton's laws to find out how much mass you need to create a 1g "force" at some fixed distance from your collection of photons. That's how you solve that problem.
Light has energy, energy is equivalent to mass, and mass exerts gravitational force. Thus, light creates gravity, i.e. the bending of space-time.
As for how much gravity, it would depend on how much energy. Thus, in order for light to generate a gravitational field like that of the Earth, it would need to have the mass (energy) of the Earth.Here's how to calculate your answer:
The Earth is a sphere of 40,000 km circumference. You can calculate the radius from that (C = 2*pi*r). The volume of the Earth isV = (4/3)*pi*r3. The mass of the Earth is M = rho*V. Rho the Earth's average density, is approximately 5.5 grams per cubic centimeter.
Once you have the mass, E = M*c2, where c is the speed of light (300,000 km/second), and E is the energy. Finally, a photon has an energy of E = h*nu, where nu is the frequency and h is Planck's constant, which is 6.626*10-33 Joules - seconds. Last, frequency is 1/wavelength.
If you want to divide your photon into multiple photons, just divide the energy by the number of photons before calculating the frequency. Remember to keep your units straight, or else you will be off by orders of magnitude!
It's very inefficient at bending space time. You could calculate it from E=mc2 and E=hc/lambda, where lambda is the wavelength of light (400nm for blue light, 700nm for red).
You need a *LOT* of light or energy to make up for even a small amount of mass.
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