Queston about the darkness of the universe

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In summary, during a TED talk by David Deutsch, he discussed a "typical place" in the universe that is far from any stars or galaxies and would appear completely black. This is due to the extremely faint light from distant objects being too dim to be seen by the human eye. However, with the use of telescopes, we are able to see these objects and understand that even in the seemingly empty areas of the universe, there is still light present. It is amazing to think that even in the vastness of the universe, we are still surrounded by objects that emit light, but our eyes are simply not sensitive enough to see it.
  • #1
phinds
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While listening to a talk on TED by David Deutsch (the talk was "Our Place in the Cosmos" from July 2005), he made a statement which just dumbfounded me. He certainly sounded like a knowledgeable guy in the rest of the talk, but here's what he said. I would appreciate any comments on this.

This is NOT an exact quote or even close, but it IS an exact representation of the meaning of what he said.

A typical place in the universe would be far away from any stars or galaxies and would be, visually, TOTALLY BLACK. You would not see anything. No stars, no galaxies, nothing. In fact, if you were looking in the direction of a typical-distance super-nova at the time when its light arrived at your location it would be so faint that you would not see anything.

HUH ?
 
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  • #2
In a "typical place" you might be a few 100 mega light years from the nearest galaxy, and its brightest zone is ~0.1 Mly across, which would appear about a minute of arc across. Surface brightness is only a few micro lightwatts/sq meter, which is barely perceivable when looking straight at it (but more perceivable looking off your center of vision, where resolution is lower). These 1-minute-across objects would be almost impossible to see directly, but they would be visible with mid-sized binos with a sufficient exit pupil.
 
  • #3
OK, thanks. That helps me understand the galaxies (and certainly therefore the stars), but how about the supernova?
 
  • #4
A supernova may be as bright as a galaxy. Same power output, spread over a minimum resolvable 1 minute, equals same apparent brightness as a galaxy.
 
  • #5
I'm really amazed. Thanks for the clear explanation.
 
  • #6
This is similar to looking up at the sky at night and seeing blackness between the visible stars. There is most definitely light there, but our eyes are not sensitive enough to see it. A telescope works by having a mirror collect light from a much greater surface area than our eye and focusing it down to a point about the size of our eye. I have a telescope with a 6 inch mirror on it. It collects around 1000 times more light than my eye, allowing me to see things that are many many times fainter than I could see otherwise. Even the Hubble Space Telescope works pretty much the exact same way.
 
  • #7
Drakkith said:
This is similar to looking up at the sky at night and seeing blackness between the visible stars. There is most definitely light there, but our eyes are not sensitive enough to see it.

Cool explanation!
 
  • #8
Drakkith said:
This is similar to looking up at the sky at night and seeing blackness between the visible stars. There is most definitely light there, but our eyes are not sensitive enough to see it. A telescope works by having a mirror collect light from a much greater surface area than our eye and focusing it down to a point about the size of our eye. I have a telescope with a 6 inch mirror on it. It collects around 1000 times more light than my eye, allowing me to see things that are many many times fainter than I could see otherwise. Even the Hubble Space Telescope works pretty much the exact same way.

Yes, I understand and completely agree w/ what you are saying, but I think you missed the point of my question. You specifically say that to see a dark area, you have to look where there aren't any stars or galaxies BUT my point was that I find it amazing that you could be ANYWHERE in the universe and face total black in all directions ... that is, everywhere you look you are looking at where you can't see anything. If, from the earth, you look away from the band of the milky way, you will be looking on at least some objects that are very far away, and it surprises me to think that all of them are still so close as to support the explanation given by BillSaltLake. I'm not saying that I find that explanation wrong, just that I find it quite amazing. Your own experience seem to support what I'm saying, unless I misunderstand you.
 
  • #9
Phinds, what I mean is that both are the same effect. Between the visible stars in the sky are dmmer stars and galaxies. If you are in the middle of nowhere you might not be able to see anything, not because there isn't anything there to see, but because the light is too faint no matter which direction you look. The only reason the stars in the night sky are visible is because of a combination of their brightness and their distance from us. (Meaning that most are very bright stars that are relatively close to us.) For example, the star Sirius, the brightest star in the northern sky, is very very close to us on a stellar scale, only 8.6 light years away and is 25 times as luminous as the sun. On the other hand, Rigel, the brightest star in the constellation Orion, is less bright to us on earth, yet Rigel is 3400 times as luminous as Sirius is, or 85,000 times that of the sun. It is less bright to us because it is 700-900 light years distant, about 100 times as far as Sirius is.

Out of all the stars visible to the naked eye in the night sky, over 95% of them are MORE luminous than our sun. But get this, 90+% of all stars in our Galaxy are LESS luminous than our sun. This means that only the very brightest or very closest of all stars are visible to us. If ours eyes were able to discern single photons, the night sky would be covered in light. Since we cannot, we only see the brightest and closest stars to us.

Yes, it is amazing when you think of the enormous distances between us and the visible stars, yet when you compare this to the scale of the universe it is almost nothing.
 
  • #10
Another fun fact: only about 6000 or so stars are distinguishable by the naked eye, while our galaxy includes roughly 400,000,000,000 stars.
 
  • #11
I think my biggest point of confusion about all this is that I clearly recalled reading that there had been observations of galaxies and supernova from billions of light years off, BUT what I cleverly forgot was that none of that was with the naked eye and in fact some of it was with in the Hubble Deep Field observations which is WAY far from naked eye.

I stand amazed and corrected.
 

FAQ: Queston about the darkness of the universe

1. What is the darkness of the universe?

The darkness of the universe refers to the vast expanse of space that appears to be empty and devoid of light. This includes the areas between galaxies and even within galaxies where there are no stars or other sources of visible light.

2. Why is the universe dark?

The universe appears dark because light can only travel so far in the vast expanse of space. As the universe expands, the light from distant objects gets stretched out, making it difficult for us to detect. In addition, there are large amounts of dust and gas in space that can block or absorb light, contributing to the darkness of the universe.

3. Can we see any light from the darkness of the universe?

Yes, there are various forms of light that can be detected from the darkness of the universe. These include radio waves, microwaves, and infrared radiation. Scientists also use specialized telescopes and instruments to detect and study these forms of light, giving us a better understanding of the universe's darkness.

4. What does the darkness of the universe tell us about the origins of the universe?

The darkness of the universe plays a crucial role in our understanding of the origins of the universe. By studying the amount and distribution of dark matter and dark energy, which make up a majority of the universe's mass, scientists can learn more about how the universe formed and evolved over time. The darkness of the universe also raises questions about the existence of other forms of matter and energy that we have yet to discover.

5. How does the darkness of the universe impact our daily lives?

The darkness of the universe may seem distant and irrelevant to our daily lives, but it has led to many technological advancements. The study of dark matter and dark energy has contributed to the development of new telescopes and instruments that have improved our understanding of the universe. Additionally, the study of the darkness of the universe has sparked curiosity and encouraged scientific inquiry, leading to a better understanding of our place in the cosmos.

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