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Is each of those spirals really the size of our whole galaxy? And if we were to zoom in 100x more, would there be just as many galaxies to see, or is there a pe

Is each of those spirals really the size of our whole galaxy? And if we were to zoom in 100x more, would there be just as many galaxies to see, or is there a perceivable outer edge to our universe's expansion?

dougmwne 4y ago
That and more. Currently we think there are 2 trillion of those little dots in the observable universe. There have been some very interesting whole sky surveys that have mapped many of them. The Sloan Digital Sky Survey has data on location, distance and spectroscopy on 50 million of the little buggers. They have some neat 3D maps, think milk being stirred into the black coffee of the vast.
- peter303 4y ago
  I read the count of "observed" galaxies is 170 billion, i.e. extrapolating the deep field count. Certain assumptions about faint and redshifted galaxies increases that number to about trillion. Early galaxies may not look as regular and spirally as recent galaxies. JWST will see more detail in the early universe to better quantify this.
  - dougmwne 4y ago
    Yes, if we were to take our best image ever, the Hubble eXtreme Deep Field and multiply it by the whole sky, we would likely see 176 billion galaxies using that same telescope and exposure. That could be considered a lower limit. But we also have models of mass and galaxy formation that suggest the number of galaxies within the observable universe is many times larger, maybe up to 2 trillion. Hubble cannot see everything at every wavelength, even if we have unobstructed line of sight to it.
dougmwne 4y ago
And to answer the questions you edited in, yes, there is an edge to the universe. It is the literal edge of time, the moment when everything was one and infinite (a singularity, we think). This edge is 13.8 billion light years in every direction. As we look far away and back in time, we can see the whole history of everything, from just after the universe cooled and expanded enough to be transparent to light, to the first protogalaxies and all the development of everything up until our very noses.
- SnowProblem 4y ago
  Thank you for the answers. It's all amazing to think about. It seemed strange to me when reading your comment, for example, that the universe would look the same age in every direction. Why? Are we close to the center? And then it hit me (probably not for the first or last time): we can only see as far as light had time to travel here! In reality the universe just keeps going.
  - dougmwne 4y ago
    Yup, we are at the center because we are the observer. Presumably everyone anywhere would appear to be at the center, just as you appear to be the center of your world and I appear to be the center of mine.
  - SAI_Peregrinus 4y ago
    Possibly. The data is consistent with an infinite universe, that expanded, and so we can only see a finite portion of it (back to the CMB). It's also consistent with a finite universe, that expanded, and so we can only see a small portion of it...
nsilvestri 4y ago
Looking this far into the past is partially about zooming in, and another part about the wavelength of the light. JWST being in infrared means that it can see things further away which have been redshifted so far that they are no longer visible to the human eye. As you look farther and farther, objects actually appear bigger, because the universe was smaller and the objects were closer at the time the light from them was emitted. At the end of it is the Cosmic Microwave Background, which is the first light that was able to travel when the universe became transparent enough that photons weren't immediately reabsorbed.
- anon_123g987 4y ago
  Angular Diameter Turnaround: https://xkcd.com/2622/ https://xkcd.com/2622/.

dougmwne 4y ago

That and more. Currently we think there are 2 trillion of those little dots in the observable universe. There have been some very interesting whole sky surveys that have mapped many of them. The Sloan Digital Sky Survey has data on location, distance and spectroscopy on 50 million of the little buggers. They have some neat 3D maps, think milk being stirred into the black coffee of the vast.

peter303 4y ago
I read the count of "observed" galaxies is 170 billion, i.e. extrapolating the deep field count. Certain assumptions about faint and redshifted galaxies increases that number to about trillion. Early galaxies may not look as regular and spirally as recent galaxies. JWST will see more detail in the early universe to better quantify this.
- dougmwne 4y ago
  Yes, if we were to take our best image ever, the Hubble eXtreme Deep Field and multiply it by the whole sky, we would likely see 176 billion galaxies using that same telescope and exposure. That could be considered a lower limit. But we also have models of mass and galaxy formation that suggest the number of galaxies within the observable universe is many times larger, maybe up to 2 trillion. Hubble cannot see everything at every wavelength, even if we have unobstructed line of sight to it.

dougmwne 4y ago

And to answer the questions you edited in, yes, there is an edge to the universe. It is the literal edge of time, the moment when everything was one and infinite (a singularity, we think). This edge is 13.8 billion light years in every direction. As we look far away and back in time, we can see the whole history of everything, from just after the universe cooled and expanded enough to be transparent to light, to the first protogalaxies and all the development of everything up until our very noses.

SnowProblem 4y ago
Thank you for the answers. It's all amazing to think about. It seemed strange to me when reading your comment, for example, that the universe would look the same age in every direction. Why? Are we close to the center? And then it hit me (probably not for the first or last time): we can only see as far as light had time to travel here! In reality the universe just keeps going.
- dougmwne 4y ago
  Yup, we are at the center because we are the observer. Presumably everyone anywhere would appear to be at the center, just as you appear to be the center of your world and I appear to be the center of mine.
- SAI_Peregrinus 4y ago
  Possibly. The data is consistent with an infinite universe, that expanded, and so we can only see a finite portion of it (back to the CMB). It's also consistent with a finite universe, that expanded, and so we can only see a small portion of it...

nsilvestri 4y ago

Looking this far into the past is partially about zooming in, and another part about the wavelength of the light. JWST being in infrared means that it can see things further away which have been redshifted so far that they are no longer visible to the human eye. As you look farther and farther, objects actually appear bigger, because the universe was smaller and the objects were closer at the time the light from them was emitted. At the end of it is the Cosmic Microwave Background, which is the first light that was able to travel when the universe became transparent enough that photons weren't immediately reabsorbed.

anon_123g987 4y ago
Angular Diameter Turnaround: https://xkcd.com/2622/ https://xkcd.com/2622/.