Register to reply

Einstein Luminosity and Speed of Light

by kornha
Tags: einstein, light, luminosity, speed
Share this thread:
Feb6-13, 05:48 PM
P: 2
1. The problem statement, all variables and given/known data
Find the Einstein luminosity (LE) in terms of just c and G (the speed of light
and the gravitational constant), i.e. determine a power (in watts) from just these two terms
using dimensional analysis. What is this value? Once determined, you should be able to
show that an object converting its mass entirely to energy cannot radiate that energy away
fast enough before becoming a black hole if its luminosity is greater than 0:5LE. Thus LE
represents an upper limit on how bright anything in our universe can be!

2. Relevant equations
There are no particular relevant equations. It helps to know that G is n m^3/(kg s^2) units and that c is m/s. Luminosity also equals Power.

3. The attempt at a solution
I solved the beginning. I found that the units of power are J/s which end up being (kg ms^2)/(s^3) and thus solving for a c and G combination yields that L = c^5/G.
However, I am completely unsure how to procede in the question passed the "Once determined you should be able to show..."
Please, any help would be great!
Phys.Org News Partner Science news on
'Smart material' chin strap harvests energy from chewing
King Richard III died painfully on battlefield
Capturing ancient Maya sites from both a rat's and a 'bat's eye view'
Feb6-13, 09:45 PM
P: 1
Please do your 250 homework by yourself.
Feb11-13, 04:44 PM
P: 1
Black holes sound ominous...

I recommend you enroll in Yoga Instructor's restorative yoga class to relax the body...and mind. 15% discount for physics majors!

Feb12-13, 04:18 AM
P: 939
Einstein Luminosity and Speed of Light

Hmm, what odd responses you got... So anyway, consider radiation moving away from the source at the speed of light. How much energy is contained in a sphere of radius ct and how much is needed to collapse it into a black hole?

Register to reply

Related Discussions
Einstein's special relativity beyond the speed of light Special & General Relativity 11
Einstein on his discovery of the speed of light General Physics 17
Transitivity condition for Einstein synchronization and the one-way light speed Special & General Relativity 50
Einstein's second postulate (one-way speed of light) Special & General Relativity 2
Einstein and idea that nothing can travel faster than the speed of light Special & General Relativity 51