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

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

### 4 Answers

- 7 years agoFavorite Answer
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.

- MikeLv 77 years ago
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.

- MorningfoxLv 77 years ago
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.

- Anonymous7 years ago
Heisenberg say we cant measure this.