Slashdot Mirror
Astronomers Measure Total Starlight Emitted Over 13.7 Billion Years (theguardian.com)
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."
I counted 156 more than that Maybe time for a recount
Yep. Take the easy path.
People have been doing it for millennia.
No sig today...
The headlines says they measured it, but then the summary says they estimated it.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
... 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.
Bach says it all.
So you think astronomers built an apparatus capable of measuring every photon emitted over the last 13.7 billion years? Title of this article is so incorrect editors should go back to primary school.
You can never know everything, and part of what you do know will always be wrong. Perhaps even the most important part.
Dust particle? Insignificant? My home, this is!
why?
what is this information useful for?
Something cannot come from nothing. It has to come from something else. Unless the something else is boring and you want to turn it into something more. Otherwise, be accurate!!!
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.
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.
that's not many photons, should be 4x10^84
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.)
How is the Riemann zeta function like Trump rallies? Both have an endless number of trivial zeros.
Quantum fluctuaton creates pairs of something from nothing.
Except that's not correct, unless you consider energy to be nothing.
Fascism: An authoritarian and nationalistic right-wing system of government and social organization. See also: NAZI's
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.
Starships were meant to fly, Hands up and touch the sky - Nicky Minaj
...it's kind of bright.
It's amazing how (contemporary) physics re-traces the history of rational theology.
I too came here to say that this is just warmed-over Lawrence Krauss.
That's not a very large number of photons. Is it just my browser that is eating the up-arrow between 10 and 84?
Quantum fluctuatons is "something".
Yes, but it's a something that comes from nothing (by definition).
10^84 = 10^42 * 10^42
Coincidence? I think not
https://app.box.com/WitthoftResume Code: https://github.com/cellocgw
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. The speed of light (c) being 299792458 m/s. (IIRC)
So mass (m) = E / c^2 = 1.32521403x10^+66 Joules / 299792458^2 = 1.4744994647625417x10^+49 Kilograms.
That's IF I have that figured right.
Now...
Mass our of Sun (one solar mass) is approximately 1.989x10^30 kilograms.
Estimates for the Mass of our galaxy range from 5.8x10^11 to 4.5x10^12 Solar Masses.
Which would put the MASS of all that starlight somewhere between 1,647,393 and 12,781,500 Milky Way GALAXIES!!! (Mind you, that assumes all starlight is orange, nothing higher or lower in energy, just for back of the envelope figuring.)
If any physicists are still reading...
Does all that mass exert any gravitational effects?
Thx.
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.
I'll take the "offtopic" hit, but whenever I see a post about starlight, I believe this should be posted.
https://youtu.be/FhKJgqxNDD8
You are welcome on my lawn.
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"
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 over Newton's theory.
Massless particles like photons don't really have a rest frame. You can let them bounce around inside a box however, and that box can have a rest frame. Generally we have E^2 = p^2c^2 + m^2c^4. Inside the box the overall momentum can be zero and you get E=mc^2. When not confined, then we have m=0 and E=pc.
The observable universe does not confine photons, so that would not count. Photons (and whole galaxies even), escape the observable universe.
4^1084 is about 4.2*10^652
So you meant to say that 4x1084 = 4^1084 ?
Write boring code, not shiny code!
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 at one point in space. We fire the lasers such that the photons meet at the same time from many different directions. If we successfully get enough photons with enough energy in a small enough volume, then they curve spacetime to the extent that a black hole is formed. If we made one large enough that it did not quickly evaporate, and managed fire in as many photons as you're describing it would be bigger than any black hole so far discovered.
That's the theory anyway. We can't really do this experiment of course or anything close to it. It is quite extreme and heavily contrived. For further reading look up "kugelblitz". If you want a possibly real scenario where photons dominated then look up "photon epoch". Is this the sort of thing you were looking for?
Because this is over a period of ~15 billion years where photons are constantly created and destroyed, not an instant snapshot of the universe.
#naabhaprzrag, #sverubfr-000, #agi-fcbafberq, negvpyr[pynff*=' negvpyr-ary-'] { qvfcynl: abar !vzcbegnag; }
n/t