Anonymous
Anonymous asked in Science & MathematicsAstronomy & Space · 7 years ago

# How many photons in 1 cm3 of space per sec.?

In other words, is it measurable and what is the number

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The best way to determine how many photons pass through a specific space is to measure the energy over a certain area as well as the frequency of the photons

For instance, let's suppose that we're looking at a square meter space that is receiving 1 kW of energy and let's say that all of the photons are infrared with a frequency of 1 THz (10^12 Hertz). How many photons are striking each second?

Well, 1 kW = 1000 J/s

Now, let's figure out the energy in each photon

E = h * f, where h is the Planck Constant

h = 6.626 * 10^(-34) Js

f = 10^12 (1/s)

E = 6.626 * 10^(-34) * 10^12 Js(1/s) = 6.626 * 10^(-22) Joules

That's the energy each photon carries

1000 / (6.626 * 10^(-22)) =>

10^3 * 10^22 / 6.626 =>

10 * 10^24 / 6.626 =>

1.509 * 10^24

That's how many photons are passing through that square meter each second.

• Well... you are mixing up some terminology.

To start off - you are (almost certainly) asking about number of photons going through an *area* per second (not a volume).

And the answer, of course, is: it depends.

Mostly it depends upon how many photons are being put out each second by your light source - and how close you are to the source.

But yes - it is measurable to some degree.

• On average in the whole universe, there are about 411 photons per cubic centimeter. That's not "per sec", that's all the time. When the photons leave any particular cm^3, another batch come in.

You also need to realize that the average cm^3 of space is far, far away from any galaxies. We happen to be deep inside a galaxy, that is deep inside a cluster of galaxies. But most of the universe is the space outside of galaxy clusters.

• Anonymous
7 years ago

Heisenberg say we cant measure this.