Comments on: The Universe so bright, it’s gotta wear shades

By: Tod

Tod — Sun, 18 May 2008 06:21:25 +0000

Phil, thanks again for yet another fascinating post. I loved the picture and I learned a bit from your lucid explanation.

Keep them coming!

By: bswift

bswift — Sat, 17 May 2008 21:14:27 +0000

Varn Nine, I corrected myself in my hasty response to ShavenYak about 9 seconds after I posted it. Thanks.

By: ShavenYak

ShavenYak — Fri, 16 May 2008 15:51:16 +0000

Thank you Varn Nine, for saving me the trouble of typing all that.

By: Gary Crowell

Gary Crowell — Fri, 16 May 2008 14:29:38 +0000

‘That’s enough energy to run a typical American house for… let’s see… carry the two… a gazillion years. More or less.’

… or Al Gore’s house for maybe a day and a half.

By: Varn Nine

Varn Nine — Fri, 16 May 2008 13:45:03 +0000

Ever since I saw that ’someone is wrong on the internet’ post by xkcd, I can’t leave these things alone.

If you want numbers, then on average, stars in the nearby Universe produce about 4,600,000,000,000,000 Watts per cubic light year, but we see only 2,600,000,000,000,000 Watts of it. The rest is absorbed by dust. That’s enough energy to run a typical American house for… let’s see… carry the two… a gazillion years.

Scientists usually aren’t unclear on Units of Measure as such, but they sometimes speak fast and use words in their ‘civilian’ context (I used to wax raging when hippies would talk about energy), not stopping to think someone who thinks less clearly will be confused. Power and energy look pretty much the same to a layperson.

Energy is the inherent ability to do work, and has the same units as work. Power is work done or energy transmitted (or wasted, or created) per time unit. If the Universe produces 4.6E15 Watts, this means Joules per second, or roughly how many kilograms you could lift one meter high each second in Earth gravity. In an hour, the energy thus accrued would be 4.6E12 kWh.

So in an hour (if the new model is correct), a typical cubic light year of your local Universe creates $460 billion worth of power.

I’d have to agree with ShavenYak and disagree with bswift. Strictly speaking, you put a price tag on energy, not power.

By: madge

madge — Fri, 16 May 2008 05:59:01 +0000

Sorry about the mess : (madge dons her rubber gloves and whips out her feather duster to clean up : ) Prolly caused by my son! I seem to spend my life clearing up after him. Age 13, a science geek par excellence and yet can’t work a vacuum cleaner! Sheesh

By: Dave Kary

Dave Kary — Fri, 16 May 2008 04:36:38 +0000

At the moment I’m a little too tired to start digging through the paper, so I’m probably just missing something obvious here. But as I look at the abstract there is one thing that bothers me. It describes the attenuation at specific wavelengths, but as I recall from our discussion of Obler’s Paradox back in cosmology class, on any meaningful timescale dust can only redistribute the light to different wavelengths, it can’t really eliminate it. So if this dust is absorbing 87% of the light at 2.1 microns, that just means that there is a lot more light coming out at some other wavelength, probably out at 10, 20 or 30 microns instead.

So, haven’t people already been observing the amount of light coming out of galaxies in the far infrared (and maybe even microwave bands)? And if so, hasn’t that been included in the typical mass-to-light ratios for those galaxies?