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Note that the most distant astronomical object we've observed has a redshift of 11, corresponding to a light travel distance of 13.4Gly. This means that if our

by cygx 6y ago

Note that the most distant astronomical object we've observed has a redshift of 11, corresponding to a light travel distance of 13.4Gly. This means that if our models are correct and the universe is indeed about 13.8 billion years old, then we've seen 97% of the universe's history. Including the microwave background in that pushes the number to 99.997%.

AnHonestComment 6y ago
....no? We have a sampling of data from 99.997% of the timeline — but the sample itself is extremely sparse.
horsawlarway 6y ago
You have an observational slice of about 4000 years at the most generous, 400 years more leniently (telescope invention was ~1600s), 40 years for modern tools (OAO-2 in the late 1960s). You might as well be looking at a single frame of a movie and telling me you know the whole plotline because it happens to have the same pixels on screen for the whole shebang.
- gpderetta 6y ago
  But that specific frame has all the previous frames imprinted and increasingly faint in some sort of cosmological motion blur.
pdonis 6y ago
> the most distant astronomical object we've observed has a redshift of 11 And even though that seems like a large distance, it is a very small redshift compared to the total time the universe has existed. The cosmic microwave radiation background, for comparison, was emitted at a redshift of about 1100. So a redshift of 11 only covers 1 percent of the expansion of the universe since the CMBR was emitted. > we've seen 97% of the universe's history No, we haven't. See above. > Including the microwave background in that pushes the number to 99.997%. No, it doesn't, because even though we can see the CMBR, we can't see anything useful in between its redshift and the redshift of 11--not because there's nothing there, but because what's there is too distorted and faint to see. (The only reason we can see the CMBR is that it's black body radiation at a temperature we can independently predict from our knowledge of the physics of recombination, so we can tailor extremely sensitive instruments to looking for its precise signature.) So there is a lot of universe that we haven't seen.
- cygx 6y ago
  No, we haven't. See above. No we have. See above: While redshift goes all the way up to infinity, in terms of cosmological time, there's still only 0.4 billion years between z=11 and z=∞, or about 3% of the age of the universe.
  - horsawlarway 6y ago
    To quote you above: > if our models are correct What is this whole discussion about? You're arguing a stance that assumes the model is correct in a discussion about the risks of assuming the model is correct. But trust me - our model is not correct.
  - pdonis 6y ago
    > there's still only 0.4 billion years In terms of time, yes. I was thinking in terms of observable spacetime volume. Even though there's only about 0.4 billion years before z = 11, the scale factor increased by a huge factor during that time (a factor of 100 from CMBR emission at z = 1100 to z = 11). That's a lot of spacetime volume from which we have no useful observations.

by cygx 6y ago

AnHonestComment 6y ago

....no? We have a sampling of data from 99.997% of the timeline — but the sample itself is extremely sparse.

horsawlarway 6y ago

You have an observational slice of about 4000 years at the most generous, 400 years more leniently (telescope invention was ~1600s), 40 years for modern tools (OAO-2 in the late 1960s). You might as well be looking at a single frame of a movie and telling me you know the whole plotline because it happens to have the same pixels on screen for the whole shebang.

gpderetta 6y ago
But that specific frame has all the previous frames imprinted and increasingly faint in some sort of cosmological motion blur.

pdonis 6y ago

> the most distant astronomical object we've observed has a redshift of 11 And even though that seems like a large distance, it is a very small redshift compared to the total time the universe has existed. The cosmic microwave radiation background, for comparison, was emitted at a redshift of about 1100. So a redshift of 11 only covers 1 percent of the expansion of the universe since the CMBR was emitted. > we've seen 97% of the universe's history No, we haven't. See above. > Including the microwave background in that pushes the number to 99.997%. No, it doesn't, because even though we can see the CMBR, we can't see anything useful in between its redshift and the redshift of 11--not because there's nothing there, but because what's there is too distorted and faint to see. (The only reason we can see the CMBR is that it's black body radiation at a temperature we can independently predict from our knowledge of the physics of recombination, so we can tailor extremely sensitive instruments to looking for its precise signature.) So there is a lot of universe that we haven't seen.

cygx 6y ago
No, we haven't. See above. No we have. See above: While redshift goes all the way up to infinity, in terms of cosmological time, there's still only 0.4 billion years between z=11 and z=∞, or about 3% of the age of the universe.
- horsawlarway 6y ago
  To quote you above: > if our models are correct What is this whole discussion about? You're arguing a stance that assumes the model is correct in a discussion about the risks of assuming the model is correct. But trust me - our model is not correct.
- pdonis 6y ago
  > there's still only 0.4 billion years In terms of time, yes. I was thinking in terms of observable spacetime volume. Even though there's only about 0.4 billion years before z = 11, the scale factor increased by a huge factor during that time (a factor of 100 from CMBR emission at z = 1100 to z = 11). That's a lot of spacetime volume from which we have no useful observations.