Astronomers Measure Total Starlight Emitted Over 13.7 Billion Years (theguardian.com) 108
Astronomers have measured all the light from all the stars that have ever existed. "In total, the astronomers estimate, stars have radiated 4x1084 photons (a photon being the smallest unit of light)," reports The Guardian. "Or put another way: 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons." From the report: The astronomers based their calculation on measurements of the extragalactic background light (EBL), a cosmic fog of radiation that has been accumulating since stars first illuminated the dark, vast expanse of space. More than 90% of starlight ends up surviving in this dim backdrop of radiation. The latest observations, collected over nine years by Nasa's Fermi space telescope, use the light from blazars -- super-massive black holes that emit powerful jets of gamma rays -- as beacons to illuminate the cosmic fog.
In total, the team captured signals from 739 blazars -- some relatively close and some extremely distant, whose light was emitted in the ancient universe and has taken billions of years to arrive at Earth. Gamma-ray photons travelling through a fog of starlight have a high chance of being absorbed. So by taking blazars at different distances from the Earth and working out how much of their radiation had been lost along the way, the total starlight at different time periods could be ascertained. The researchers used a computer model to factor in the cosmic fog, which "is simultaneously being diluted as the universe expands and space itself is stretched out," the report mentions. "The measurements suggest that star formation peaked about 11 billion years ago and has been on the wane ever since. About seven new stars are created in our Milky Way galaxy every year."
In total, the team captured signals from 739 blazars -- some relatively close and some extremely distant, whose light was emitted in the ancient universe and has taken billions of years to arrive at Earth. Gamma-ray photons travelling through a fog of starlight have a high chance of being absorbed. So by taking blazars at different distances from the Earth and working out how much of their radiation had been lost along the way, the total starlight at different time periods could be ascertained. The researchers used a computer model to factor in the cosmic fog, which "is simultaneously being diluted as the universe expands and space itself is stretched out," the report mentions. "The measurements suggest that star formation peaked about 11 billion years ago and has been on the wane ever since. About seven new stars are created in our Milky Way galaxy every year."
Hmm (Score:2)
Re:Hmm (Score:5, Informative)
Add to it the typo in the article. 4x1084 - that's not many photons, should be 4x10^84.
Maybe Slashdot trimmed off the "sup" html tag though.
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He's a moron. Then again, all of /.'s editors are worthless; I don't think I've ever seen them correct a single article.
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Re:Hmm (Score:4, Insightful)
Indeed, that left me scratching my head. Did the editors not get past seventh grade?
Re: (Score:2, Offtopic)
Why is there an "insightful" mod and why isn't it "-1"? If I wanted insight, I wouldn't be reading /.
And why isn't there a "+1" Troll alternative too? :)
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When I have mod points, I enjoy finding a "0, Troll" post that I think was unfairly modded down, because I can give it an Underrated mod and change it to "1, Troll". Often that's actually a fair description of the post, where they're sort of half-trolling, but they make a good point.
Unfortunately, the (very) rare time I've found a "1, Troll" post to give a second Underrated mod, it doesn't go to "2, Troll", which is sad. I think it just makes the description disappear. Also, if there's any non-Underrated m
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Uncertainty (Score:2)
that's not many photons, should be 4x10^84
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4^1084 is about 4.2*10^652
So you meant to say that 4x1084 = 4^1084 ?
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4x10^84 works for me. But in all my years of programming, spreadsheets, and scientific calculator work, I've wondered why the simpler 4E84 exponential notation has not become more popular in text media.
Any thoughts?
Are there any /. readers out there that don't understand 4E84?
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Are there any /. readers out there that don't understand 4E84?
Sorry, we didn't learn that geeky hexadecimal stuff in physics class.That's NaN.
4x10^84 takes up WAS more space and thus is WAY more precise!
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... should be 4x10^84.
My grandfather says 4x10^83 should be enough for anyone.
"Measure" (Score:4, Informative)
The headlines says they measured it, but then the summary says they estimated it.
Re:"Measure" (Score:5, Insightful)
The Guardian author seems to think the universe is finite and of known size.
The scientists' 4x10^84 presumably is an estimate for the observable universe.
Re:"Measure" (Score:5, Funny)
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The delayed-choice quantum eraser [wikipedia.org] strongly implies that multiple states at the same time are the only reasonable explanation. It can't just be "shut up and calculate" forever.
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Re: "Measure" (Score:1)
Black cats = dark matter
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4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
Would be great if mathematicians could invent something to avoid writing 100's of zeroes, something like 10^?
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You should stand in science centers and museums where they write large numbers like this on displays to make it easier to visualize how large a number it is, and point out to passing people that there's a shorter way of writing it. Hell, you could dedicate your entire life to being a tedious bore on a mission to educate nobody!
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Four septenvigintillion.
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Yeah, I noticed that too. OTOH I often make estimates when I measure things, and a pedant would submit that *all* measurements are estimates.
No, it's not all stars ... (Score:1)
... but in fact all the stars known to scientists and an estimate as well. There might be so much more light emitted by not yet discovered stars.
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y tho? (Score:2)
why?
what is this information useful for?
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Of what use is a newborn baby?
Just look at this as one of the up sides of Big Data. Someone or something crunched a bunch of numbers together that nobody had crunched together before and came up with an interesting result that might spark further thoughts.
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There's good eating on one of those. http://www.gutenberg.org/ebook... [gutenberg.org]
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This is what Science should really be about (Score:2, Insightful)
Just think, if they hadn't published this paper, we might not have known, to a high degree of accuracy, the exact number of photons emitted over the lifetime of the universe.
I can't decide whether this trumps Ugg's famous theorem that striking pieces of flint together summons the fire element from the Fire God in the Sky.
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a high degree of accuracy, the exact number
Not sure if trolling...
What? (Score:1)
What kind of fog is that? Photons don't absorb photons, do there must be other matter involved. Are we talking about excited states and ionisation of interstellar gas? (sorry I don't read articles)
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90% of photons from stars end up in a fog. Ok. And that fog absorbs gamma rays. What kind of fog is that? Photons don't absorb photons, do there must be other matter involved.
From the actual article in Science: "Gamma rays with sufficient energy can annihilate when they collide with EBL photons and produce electron-positron pairs (i.e., the reaction e+e–), effectively being absorbed as a result of the interaction." So yes they do, under the right conditions.
If you think about it (Score:2)
...it's kind of bright.
4x1084? (Score:2)
A quick analysis shows... (Score:4, Funny)
10^84 = 10^42 * 10^42
Coincidence? I think not
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Could somebody PLEASE check my Math & Physics! (Score:1)
So 4x10^84 photons...
Lets see here. Energy in Joules per photon = hf where h is a constant (6.626070150x10^-34 Js) and f is the frequency (1/s) of the photon according to Max Planck.
Orange light, just to pick a random frequency, is around 600nm, or around 500 Thz, and should have an energy value in Joules = hf = 6.626070150x10^-34 * 500,000,000,000,000 = 3.313035075x10^-19 Joules.
But that's per photon. So times 4x10^84 photons yields 1.32521403x10^+66 Joules.
E=mc^2. E in Joules. Mass (m) in kilograms.
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Can you check mine please? Say we have N photons and the mass of a photon is 0. Then N times 0 equals 0, making a total mass of 0? Is that right?
If the photons were confined in some kind of box, then they'd add to the mass of the box though, so you could do it that way with an imaginary box in a thought experiment, and use this e=mc^2 formula you've picked up from somewhere.
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Newton's law of universal gravitation was superseded by general relativity about 100 years ago. One reason why is because it does not model the behaviour of light in a gravitational field correctly. Einstein's cross is an example of gravitational lensing, so these massless particles are following the curvature of spacetime around a massive object. We explain it with general relativity, not Newton's theory of gravity. The case of Mercury's orbit you mention is further evidence for general relativity ove
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I appreciate my previous responses may have come across as pedantic but from my point of view I'm trying to sharpen your understanding as much as possible in a short amount of time. I'm doing it for free and I'm the only person trying to help.
It sounds like the case you're most interested in is what happens when lots of photons with lots of energy happen to meet in one spot. Suppose we had a large empty region of space and we surrounded it with lasers. These lasers are all very far away and directed a
Starless (Score:2)
I'll take the "offtopic" hit, but whenever I see a post about starlight, I believe this should be posted.
https://youtu.be/FhKJgqxNDD8 [youtu.be]
I'd love to turn you on (Score:2)
That headline reminds me of this song.
"I read the news today, oh boy
Four thousand holes in Blackburn, Lancashire
And though the holes were rather small
They had to count them all
Now they know how many holes it takes to fill the Albert Hall
I'd love to turn you"
- Lennon/McCartney "A day in a life"
What is the point of this? (Score:2)
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Yep. Take the easy path.
People have been doing it for millennia.
Re: If this isn't bullshit nothing is (Score:4, Informative)
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Re:If this isn't bullshit nothing is (Score:5, Informative)
Something cannot come from nothing. It has to come from something else.
That's not how it works. That's not how any of this works.
First of all, something comes from nothing all the time. Quantum fluctuaton creates pairs of something from nothing. Most of these disappear extremely quickly, but due to location being a probability, not a fact, a few must by necessity survive. Our whole universe may be no more than the result of a single vacuum fluctuation, see inflationary theory.
Secondly, "come from" implies time. The concept of time itself breaks down near singularities, making the rule of "something must come from nothing" meaningless in that context. "What was before big bang?" requires a definition of "before" that doesn't imply time ticking or having an arrow.
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Quantum fluctuatons is "something".
Yes, but it's a something that comes from nothing (by definition).
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That's not how it works. That's not how any of this works.
First of all, something comes from nothing all the time. Quantum fluctuaton creates pairs of something from nothing. Most of these disappear extremely quickly, but due to location being a probability, not a fact, a few must by necessity survive. Our whole universe may be no more than the result of a single vacuum fluctuation, see inflationary theory.
Secondly, "come from" implies time. The concept of time itself breaks down near singularities, making the rule of "something must come from nothing" meaningless in that context. "What was before big bang?" requires a definition of "before" that doesn't imply time ticking or having an arrow.
Why am I hearing this entire passage in Lawrence Krauss's voice, and imagining him waving his hands around for emphasis? I can see the Converse sneakers, the brown coat, the smarmy look...
(Mind you, this is not an attempt at an ad hominem attack: he's frequently right, even if I find him annoying after a while.)
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Quantum fluctuaton creates pairs of something from nothing.
Except that's not correct, unless you consider energy to be nothing.
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