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The deliberate use of the word "observable" when referring to the Universe, is perhaps one of the most profound changes in human thinking the Hubble Space Teles

The deliberate use of the word "observable" when referring to the Universe, is perhaps one of the most profound changes in human thinking the Hubble Space Telescope has contributed. One falls silent contemplating the images this machine has produced.

at-fates-hands 12y ago
I remember in junior high our physics teacher made a huge deal about this when they launched it in 1990. He quizzed us on the article he handed out at the beginning of class, just to make sure we didn't forget how important this was. Beyond the early failures, it has indeed achieved well beyond what I think most people imagined, bringing us closer to a world we know so little about.
rm999 12y ago
I don't think the Hubble Space Telescope has anything to do with that term. We use "observable" because the Universe is far larger than what we can ever physically see or interact with (there's a growing body of evidence that it's infinite and "flat"). The observable part is an upper bound on the part of the Universe that will ever be relevant to us. Kind of makes me feel insignificant in a weird way :) Also, the Hubble can't even see most of the Observable Universe; it can see ~15 billion lights years away, whereas the radius of the observable universe is 47 billion light years.
- rquantz 12y ago
  How is that the radius of the observable universe? I thought the observable universe was bounded by the age of the universe, which why the furthest distant observations show the universe close to the time of the Big Bang. Shouldn't the radius of the observable universe = the number of years light has been traveling toward us? Edit: Wikipedia says I'm wrong about this. What's new?
  - yk 12y ago
    The radius of the observable universe is the distance the furthest stars we could theoretically observe today.[0] So these stars were a lot closer earlier and we can see the light even though the stars are further away than the age of the universe (times the speed of light). [0] Technical details omitted.
  - vidarh 12y ago
    The universe has been expanding. So the distances now are vastly larger than they used to be when the light left its sources.
- privong 12y ago
  > Also, the Hubble can't even see most of the Observable Universe; it can see ~15 billion lights years away, whereas the radius of the observable universe is 47 billion light years. There is a subtlety with the size of the observable Universe versus the distance Hubble can see. The radius of the observable universe is 47 billion lights years (the radial distance to the cosmic microwave background[0]). Hubble has spotted galaxies whose distance corresponds to a light travel time of ~13 billion years. However, the Universe has expanded since that light was emitted 13 billion years ago, so the galaxies which emitted that light are now about 30 billion light years away. So Hubble can see objects which are closer to the edge of the observable Universe than the 13 billion year light travel time implies, compared with the size of the observable universe. There are tentative detections of even more distant galaxies. For reference, I obtained those values using Ned Wright's cosmology calculator[1] with a redshift z=8, and the default values, assuming a flat cosmology. The 13 billion years ago number is the light travel time and the 30 billion light year distance is the comoving radial distance. [0] If you plug the approximate redshift of the cosmic microwave background (z=1100) into [1], you get 45.5 billion light years. [1] http://www.astro.ucla.edu/~wright/CosmoCalc.html http://www.astro.ucla.edu/~wright/CosmoCalc.html Edit: Clarified wording and added CMB distance info.
js4 12y ago
Or the inspiration that the images have produced. As a kid Hubble photos made me fall in love with science.
- nsxwolf 12y ago
  Until I learned all the colors are fake and space is monochromatic almost everywhere.
  - Rexxar 12y ago
    It's absolutely not monochromatic. It's full of colours that we cannot see, we have to use fake colours to visualize objects from space in all their diversity.
    - nsxwolf 12y ago
      Full of colors that we cannot see. Are you saying its like watching a color TV signal on a black and white TV set? Are we just too far away? Would any of those nebulae show such beautiful colors to the human eye if we were only closer? I can never get a straight answer on that. But if you look at these objects through a small telescope, you will see white blobs.
      - cgearhart 12y ago
        Near and far infrared, ultraviolet, x-rays, gamma rays -- there are lots of photons out there. Hubble has many sensors[0], so many of the images taken are from outside the relatively small portion of the spectrum that humans can see and then mapped to the visible spectrum. Additionally, human vision is dominated by intensity sensitivity, not color sensitivity.[1] So especially with very modest optical equipment and faint light sources you won't see much color. [0]http://hubblesite.org/the_telescope/hubble_essentials/ http://hubblesite.org/the_telescope/hubble_essentials/ [1]http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.ht...
dalke 12y ago
An ngrams analysis doesn't show a significant increase in the use of "observable universe" after 1990. https://books.google.com/ngrams/graph?content=observable+universe&year_start=1930&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cobservable%20universe%3B%2Cc0 https://books.google.com/ngrams/graph?content=observable+uni... . While it does increase, it seems to continue the trend which started in the 1940s. Here's an example of Asimov using "Observable Universe" in "Asimov on Numbers" (1977): https://books.google.com/books?id=el0PAQAAMAAJ&q=observable+universe&dq=observable+universe&hl=sv&sa=X&ei=_jTlVKfiL4TCywOz7ICQCw&redir_esc=y https://books.google.com/books?id=el0PAQAAMAAJ&q=observable+... .

at-fates-hands 12y ago

I remember in junior high our physics teacher made a huge deal about this when they launched it in 1990. He quizzed us on the article he handed out at the beginning of class, just to make sure we didn't forget how important this was. Beyond the early failures, it has indeed achieved well beyond what I think most people imagined, bringing us closer to a world we know so little about.

rm999 12y ago

I don't think the Hubble Space Telescope has anything to do with that term. We use "observable" because the Universe is far larger than what we can ever physically see or interact with (there's a growing body of evidence that it's infinite and "flat"). The observable part is an upper bound on the part of the Universe that will ever be relevant to us. Kind of makes me feel insignificant in a weird way :) Also, the Hubble can't even see most of the Observable Universe; it can see ~15 billion lights years away, whereas the radius of the observable universe is 47 billion light years.

rquantz 12y ago
How is that the radius of the observable universe? I thought the observable universe was bounded by the age of the universe, which why the furthest distant observations show the universe close to the time of the Big Bang. Shouldn't the radius of the observable universe = the number of years light has been traveling toward us? Edit: Wikipedia says I'm wrong about this. What's new?
- yk 12y ago
  The radius of the observable universe is the distance the furthest stars we could theoretically observe today.[0] So these stars were a lot closer earlier and we can see the light even though the stars are further away than the age of the universe (times the speed of light). [0] Technical details omitted.
- vidarh 12y ago
  The universe has been expanding. So the distances now are vastly larger than they used to be when the light left its sources.
privong 12y ago
> Also, the Hubble can't even see most of the Observable Universe; it can see ~15 billion lights years away, whereas the radius of the observable universe is 47 billion light years. There is a subtlety with the size of the observable Universe versus the distance Hubble can see. The radius of the observable universe is 47 billion lights years (the radial distance to the cosmic microwave background[0]). Hubble has spotted galaxies whose distance corresponds to a light travel time of ~13 billion years. However, the Universe has expanded since that light was emitted 13 billion years ago, so the galaxies which emitted that light are now about 30 billion light years away. So Hubble can see objects which are closer to the edge of the observable Universe than the 13 billion year light travel time implies, compared with the size of the observable universe. There are tentative detections of even more distant galaxies. For reference, I obtained those values using Ned Wright's cosmology calculator[1] with a redshift z=8, and the default values, assuming a flat cosmology. The 13 billion years ago number is the light travel time and the 30 billion light year distance is the comoving radial distance. [0] If you plug the approximate redshift of the cosmic microwave background (z=1100) into [1], you get 45.5 billion light years. [1] http://www.astro.ucla.edu/~wright/CosmoCalc.html http://www.astro.ucla.edu/~wright/CosmoCalc.html Edit: Clarified wording and added CMB distance info.

js4 12y ago

Or the inspiration that the images have produced. As a kid Hubble photos made me fall in love with science.

nsxwolf 12y ago
Until I learned all the colors are fake and space is monochromatic almost everywhere.
- Rexxar 12y ago
  It's absolutely not monochromatic. It's full of colours that we cannot see, we have to use fake colours to visualize objects from space in all their diversity.
  - nsxwolf 12y ago
    Full of colors that we cannot see. Are you saying its like watching a color TV signal on a black and white TV set? Are we just too far away? Would any of those nebulae show such beautiful colors to the human eye if we were only closer? I can never get a straight answer on that. But if you look at these objects through a small telescope, you will see white blobs.
    - cgearhart 12y ago
      Near and far infrared, ultraviolet, x-rays, gamma rays -- there are lots of photons out there. Hubble has many sensors[0], so many of the images taken are from outside the relatively small portion of the spectrum that humans can see and then mapped to the visible spectrum. Additionally, human vision is dominated by intensity sensitivity, not color sensitivity.[1] So especially with very modest optical equipment and faint light sources you won't see much color. [0]http://hubblesite.org/the_telescope/hubble_essentials/ http://hubblesite.org/the_telescope/hubble_essentials/ [1]http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.ht...

dalke 12y ago

An ngrams analysis doesn't show a significant increase in the use of "observable universe" after 1990. https://books.google.com/ngrams/graph?content=observable+universe&year_start=1930&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cobservable%20universe%3B%2Cc0 https://books.google.com/ngrams/graph?content=observable+uni... . While it does increase, it seems to continue the trend which started in the 1940s. Here's an example of Asimov using "Observable Universe" in "Asimov on Numbers" (1977): https://books.google.com/books?id=el0PAQAAMAAJ&q=observable+universe&dq=observable+universe&hl=sv&sa=X&ei=_jTlVKfiL4TCywOz7ICQCw&redir_esc=y https://books.google.com/books?id=el0PAQAAMAAJ&q=observable+... .