Why the sky is dark in the night

https://medium.com/starts-with-a-ba...er-than-the-speed-of-light-23dff8c10f3d#.v87z

It means that as time goes on, the light emitted by distant galaxies gets shifted quite heavily towards the red part of the spectrum, resulting in a cosmological redshift.

It means that there are some portions of the Universe that are so distant that light emitted from them will never be able to reach us. Currently, that point is anything beyond about 46.1 billion light years from us.

And it means that any object beyond about 4.5 Gigaparsecs (or 14-to-15 billion light years) will never be reachable by us, or anything we do, from this point forward. All of those objects — objects making up 97% of the observable Universe by volume — are all presently beyond our reach. Even a photon, emitted right now, will never arrive at them, if that’s our destination

So yes, as time goes on, all the objects that are caught up in the expansion of the Universe will accelerate away from us, faster and faster. Let enough time go by, and all of them will eventually wind up receding faster than the speed of light, unreachable by us in principle, no matter how fast of a rocket we build or how many signals we launch and the speed of light itself.

Get our act together, and start intergalactic travel as soon as we can, before it’s too late. The Universe we have today is disappearing thanks to the accelerated expansion of space. Although no object ever moves through the fabric of space itself faster than the speed of light, there is no speed limit on the expansion of the fabric of space; it simply does as it pleases.
 
The God said:
Nonsense continues.......
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:)
But its you without references...It's you without credentials.....It's you seeing the need to insult and write off all other poster's comments that refute your position....It's you up shit creek without a paddle...:rolleyes:
But certainly you are entitled to say and think what you like, its just your rather naive expectations that anyone is taking any notice of you.
You do know where you are, right? ;)
 
As I have said a few times recently, the Uinverse is a dynamic entity that is never ceasing to change.........

https://en.wikipedia.org/wiki/Timeline_of_the_far_future

100 billion hence:
The Universe's expansion causes all galaxies beyond the former Milky Way'sLocal Group to disappear beyond the cosmic light horizon, removing them from the observable universe.

1.342×10 to 99 years from now:

Estimated time until the central black hole of S5 0014+81, as of 2015 the most massive known with the mass of 40 billion solar masses, dissipates by the emission of Hawking radiation,[91] assuming zero angular momentum (non-rotating black hole). However, the black hole is on the state of accretion, so the time it takes may be longer than stated on the left.

1.7×10 to 106 years from now:
Estimated time until a supermassive black hole with a mass of 20 trillion solar masses decays by the Hawking process.[91] This marks the end of the Black Hole Era. Beyond this time, if protons do decay, the Universe enters the Dark Era, in which all physical objects have decayed to subatomic particles, gradually winding down to their final energy state in the heat death of the universe

Check out the interesting link for more on the projected time line history of our Universe.
 
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The God said:
If you say that darkness is zero radiation...then you have to take a moment to reform your premise.
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Dave is absolutely correct: The Universe/spacetime shines at 2.7K: Darkness is relative and dependant on EMR...
The God said:
Give me a place on Earth (forget universe) which is radiation less ?? Not even best of your vacuum.
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:) Perhaps in one of your temples, churches, mosques, gurudwaras, obahai centers.
My statement as follows was tongue in cheek:
And God said “Let there be light,” and there was light. God saw that the light was good, and he separated the light from the darkness. God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning the first day.
Please do not take seriously.
 
The God said:
As bright as day....wow Pado, you can go any extent to oppose me...
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No, no not at all: I oppose your anti mainstream nonsense that's all.....I oppose your self admitted "playing games" on a science forum, to attempt to mask your many errors and indiscretions........I oppose your nonsensical conspiracy nonsense.
Again, the Universe shines at 2.7K: Dave was/is correct...you are wrong.
 
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The God said:

20 trillion is surely more than 1500 billion........
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And we are talking about 1.7X 10 to 106 years hence. BH's will get bigger before they eventually evaporate.
You really do not understand, do you?

The God said:
Paddo is on roll...thank you Paddo.
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:) On a roll? Is that all you have?
While you "play games" [to use your own words] to mask your errors and mistakes, while you continue suggesting outrageous conspiracy crap, and while you continue on your anti mainstream science rants, I'll be doing my best to show those claims and suggestions and consequently yourself, for what you are.
 
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Note that when the article said EGS8p7 was more than 13.2 billion light years away, it was referring to a light-travel-time distance. I'm not sure of the actual distance, but I envisage it's something like 44 billion light years. Also note that Hawking radiation remains conjectural, and that whilst we have evidence from WMAP and elsewhere suggesting that the universe is flat, we don't have any evidence for an infinite universe. It's a non-sequitur to say a flat universe is an infinite universe. Yes, it's in the NASA article, but that's a pop-science article. We don't know that the Universe is infinite in extent, and we cannot conclude that the Universe is much larger than the volume we can directly observe.
 
Actually, it is really more of a simultenaity convention: unless otherwise specified, events happen when you see them.
 
The God said:
3. This receding is due to accelerated expansion of universe, but there is substantial gravity which is present till a very substantial distance from the peripheral point of any such Galaxy, surely there could not be any red shift as long as the light/photon is in the Gravitational filed of any such Galaxy, so what is that point beyond which the red shifting starts....... For example there is no expansion between Andromeda and Milky Way due to Gravity, so a photon originating at MW, will not feel any red shift at least till Andromeda, the same thing should hold good for the distant Galaxy and its local surroundings.

4. If you study the Gravitational Lensing in detail, then you will come to know, that the light which is getting lensed by the Lensing Galaxy, is infact quite away (possibly millions of light years and more) from the peripheral point of the Galaxy, suggesting substantial gravity at a very far point....so there cannot be red shift till any suchn point ?
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but at what points/locations of the gravitational lensing are you referring too from the many points/locations that it would occur from while traveling through/in the cosmos? why do you, only, simply, refer to one point of gravitational lensing?
what if it was lens-ed from one galaxy and then was lens-ed again from another galaxy while traveling through the cosmos?
 
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The God said:
If you say that darkness is zero radiation...
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I don't, so not sure what your point is. Also, I don't have a premise; you asked a question that makes an assumption.

In a discussion of science, one must be careful to be unambiguous. Darkness, in a scientific context, is ambiguous, if not naive. What is dark to our eyeballs is not dark to our technology.

So, I have clarified.

The universe is awash with EMR. Your question, to be unambiguous, needs to be reformed. (Otherwise, this would be a very short thread, as origin just pointed out.)

The God said:
Give me a place on Earth (forget universe) which is radiation less ?? Not even best of your vacuum.
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Correct.

We can move forward now, with the clarification.

So what is your new question?
Presumably, it is why is there so little visible light in the universe? - but I don't want to put words in your mouth.
 
DaveC426913 said:
I don't, so not sure what your point is. Also, I don't have a premise; you asked a question that makes an assumption.

In a discussion of science, one must be careful to be unambiguous. Darkness, in a scientific context, is ambiguous, if not naive. What is dark to our eyeballs is not dark to our technology.

So, I have clarified.

The universe is awash with EMR. Your question, to be unambiguous, needs to be reformed. (Otherwise, this would be a very short thread, as origin just pointed out.)


Correct.

We can move forward now, with the clarification.

So what is your new question?
Presumably, it is why is there so little visible light in the universe? - but I don't want to put words in your mouth.
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We are not discussing the meaning of word darkness or brightness......all here who know basic Physics, understand what the darkness is in the context..

You made a statement that it is not dark, it is awashed with the radiation......technically correct but a pretty loose statement to kill the discussion........see how Paddo latched on to this.
 
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krash661 said:
but at what points/locations of the gravitational lensing are you referring too from the many points/locations that it would occur from while traveling through/in the cosmos? why do you, only, simply, refer to one point of gravitational lensing?
what if it was lens-ed from one galaxy and then was lens-ed again from another galaxy while traveling through the cosmos?
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You refer to a very profound technical point.......multiple lensing by multiple objects on the way...what a ding-dong life for poor photon..

But to answer you, the GL point is substantially away from the peripheral point of a Galaxy (Probably running into millions of light years), suggesting that such Galaxy (which can bend photon millions of light years away) will have very high gravity, kind of local (group) influence is very high and spacetime expansion should not be appreciable....So from which point onwards the spacetime expansion takes control from the Gravity ?

You will understand this better if you know that there is no spacetime expansion between Andromeda and Milky way...why ? Simply because Gravity dominates......so for a very remote galaxy, the originating light, starts redshifting from which point onwards....from the source itself or once it comes out of the local Gravity influence ?
 
The God said:
We are not discussing the meaning of word darkness or brightness......all here who know basic Physics, understand what the darkness is in the context..
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Of course we are! You're just starting another of your familiar avoidance of the issue as usual.
The God said:
You made a statement that it is not dark, it is awashed with the radiation......technically correct but a pretty loose statement to kill the discussion........see how Paddo latched on to this.
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Yep, technically and physically correct at least for anyone familiar with COBE and the CMBR at 2.7K
And of course I latched onto it, just as I have latched onto other issues you have subsequently but expectedly ignored when shown to be in error.
Do you expect to be able to spread your gospel of anti mainstream nonsense without any refutation or come back?
Think again.
 
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