# What does one calorie per cubic mile mean to you?

#### marcus

Gold Member
Dearly Missed
One calorie per cubic mile is almost exactly the same as one joule per cubic kilometer.

Because a calorie is 4.185 joules and a cubic mile is 4.166 cubic km.

And the density of the universe has finally been measured to the general satisfaction of astronomers, at 0.85 joule per cubic kilometer.
This is what makes it flat, and matches the observed acceleration of expansion and the observed bumpiness of the CMB.

As a rough size 0.85 is about one. And so roughly speaking the density of the universe is ONE joule per cubic km.

And in old-timey units (for people who can think in calories and miles) that is about one calorie per cubic mile. Actually 0.85 but about.

Tonight there will no doubt be some people on this planet who look up at the dark and think "hmmm, on average there is about a calorie in a cubic mile of that"

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#### marcus

Gold Member
Dearly Missed
the energy density of sunlight at this distance

at this distance from the sun and at any one instant how many joules of sunlight does a cubic kilometer of space contain?

or how many calories of sunlight are in a cubic mile since it is the same number

and does it matter, should we care? well it is what makes this zone that the earth orbits in the "habitable zone"
exobiologists are not averse to talking about the "habitable zone" around each star which in effect is the zone where space
has this energy density of light

I think there are around 5000 calories of sunlight per cubic mile
in space at this distance----or joules per cubic km

Order of magnitude, it is around 5000 times the overall energy density of the universe.

The present energy density 0.85 joule/km^3 overall is one of the things that makes the universe hospitable to life----flat, given its present expansion rate etc---not about to collapse on itself. So two kinds of habitability both of which can be expressed as energy densities---one being a few thousand times the other.

no time to proofread, hope no gross errors

#### cragwolf

Re: the energy density of sunlight at this distance

Originally posted by marcus
I think there are around 5000 calories of sunlight per cubic mile
in space at this distance----or joules per cubic km

Order of magnitude, it is around 5000 times the overall energy density of the universe.
You've come across another way of explaining why the sky is dark at night: there's just not enough energy out there (per unit volume one must be careful to note) to make it bright.

#### drag

Complete vacuum...

What does one calorie per cubic mile mean to you?
It means a lot more more exercise then I feel like doing if I'm going to 'lose' that sandwich I had for lunch today.

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