what would be the observations we would see and measure if . . .

[klaus54]

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Portrays the universe coming from a singularity of some kind.

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This image portrays this "singularity" at the outskirts of our observable universe.

I like this diagram of the history of the universe since it shows






The accepted view is that of an expansion. I pose the question of it collapsing. The expansion view requires a "cosmic inflation" to make it work. And now the local universe is expanding faster than the perceived past - dark energy is proposed.

The expansion "view" does NOT depending on inflation. Redshift and CBR pointed to expansion long before the inflationary epoch was proposed.

Do you have any sources proposing that the cosmos is currently in a state of collapse? If the cosmos is expanding faster than expected, why do you propose a collapse???

And if our universe started one Planck time after the singularity, in what sense is the universe being "swallowed up in a singularity" (or whatever verbiage you used)?

I like this diagram showing the universe smaller in the past:

history-of-the-universe-2015.jpg

[oxmixmudd]

Zip Code said that redshift makes things look larger.

Your not the forgiving type ... are you?


Jim

[oxmixmudd]

I see now a reason why 37818's graphics looked wrong to me. The second graphic showed a concentric series of circles. The largest circle is for the beginning of the universe. That confused me because I thought the universe just a few femtoseconds from the singularity would be smaller than we can perceive with our own unaided eyes, assuming we could survive with good vision in all that.

The diagram is actually projecting spatial points out to a sphere far larger than the size of the universe, a mapping.

yes - but it is a real depiction of what it is we actually see as we look out into the universe. And most people don't recognize that is how it works. The largest sphere we can see (the CMB) is actually a much smaller universe than the one that actually is at this 'time'. It's bizarre to think about it, but what we see is the smaller, younger, universe 'turned inside out' and literally stretched across the visual 'edge' of any observing point in the larger, older universe (see my previous post on the effect of expansion on the angular extent of objects at z>>1). It's an illusion created by light travel time and expansion, and it's not at all intuitive.


Jim

[oxmixmudd]

There is a difference between expansion and a collapse. The current view is that of an expansion. With the red shift, objects appear proportionally larger. So at some distance the objects while beyond near objects, they nevertheless are closer than the near objects larger shifted to the red. Do the math.

Velocity = Hubble's constant x distance in megaparsec. Hubble's constant = 71 km/s/megaparsec.

The red shift would by wavelength' = wavelength x sqr((c + v)/ (c - v))

Of course the constant is different in the past than it is now. It is now faster. But for simplicity to do a calculation what a red shift would be assuming the constant at a fixed rate.

It would not happen that way.

They don't appear larger just because of the red-shift. That is, the redshift doesn't change the apparent size. It's primary observational effect is to redden the image, which can change our capacity to resolve distant objects because for a given angular resolution a larger mirror is required at longer wavelengths and the longer wavelengths carry less energy per photon.

It is the expansion itself which at z>>1 results in the apparent increase in an object's angular diameter.

Jim

[klaus54]

Your not the forgiving type ... are you?


Jim

Nope! (Not online at least. Teehee...)

I think Zip was confusing the increase of wave length (redshift) with the embiggement (neologism!) of the appearance of the retreating object.

[oxmixmudd]

yes - but it is a real depiction of what it is we actually see as we look out into the universe. And most people don't recognize that is how it works. The largest sphere we can see (the CMB) is actually a much smaller universe than the one that actually is at this 'time'. It's bizarre to think about it, but what we see is the smaller, younger, universe 'turned inside out' and literally stretched across the visual 'edge' of any observing point in the larger, older universe (see my previous post on the effect of expansion on the angular extent of objects at z>>1). It's an illusion created by light travel time and expansion, and it's not at all intuitive.


Jim

one of the more interesting corollaries: Has there ever been/Will there ever be a time when the entirety of the universe at +380,000 years is visible from a single location? Clearly, at this point, what we observe in the CMB spans some pi*<13.7 billion light years> / <angular diameter increase>. Is that the entire universe at that time or only part of it? And as the universe ages, do we see more (or less) of the universe as that sphere expands. That is, is pi*<apparent radius of the universe> / <angular diameter increase> == K where K is a constant? Or do we see less over time, or will we eventually (or do we now) see it all (That answer will depend in part on the amount of increase in the expansion rate)


Jim

[37818]

I think Zip was confusing the increase of wave length (redshift) with the embiggement (neologism!) of the appearance of the retreating object.

Really? Explain then how looking back in time we are looking at the visible universe when it was smaller? The alternative being the distant past was always being see limited by wavelength and resolution do to wavelength, there never being a singularity as such. Was always infinite.

[klaus54]

Really? Explain then how looking back in time we are looking at the visible universe when it was smaller? The alternative being the distant past was always being see limited by wavelength and resolution do (sic) to wavelength, there never being a singularity as such. Was always infinite.

???

Since it's well-established that the universe is expanding, and since the speed of light is finite, OF COURSE we're looking into the past when the universe was smaller.

That's what "expanding" means, unless you have another definition.

BTW, I was correcting your garbled explanation of redshift, expansion, and embiggement. Redshift is evidence of expansion, it does not cause things to look larger!

[little_monkey]

Zip Code said that redshift makes things look larger.

More precisely, it makes things look fuzzier. To get a sharp image, short wavelengths will do the trick. So the redshift means that light coming from far away will give fuzzier pictures, that is, it will spread out over a larger area on your photographic plate, therefore appear larger.

[klaus54]

Thanks for the clarification!

[37818]

???

Since it's well-established that the universe is expanding, and since the speed of light is finite, OF COURSE we're looking into the past when the universe was smaller.

That's what "expanding" means, unless you have another definition.

BTW, I was correcting your garbled explanation of redshift, expansion, and embiggement. Redshift is evidence of expansion, it does not cause things to look larger!

If a light beam is bouncing back and forth a given distance under a red shift. And the speed of light does not change. In the red shift the time it takes the beam of light to bounce back and forth takes longer, proportional to the red shift. So did the speed of light slow down? Or is the distance now proportionately further per the red shift "embiggement?" I vote for the second option.

[klaus54]

If a light beam is bouncing back and forth a given distance under a red shift. And the speed of light does not change. In the red shift the time it takes the beam of light to bounce back and forth takes longer, proportional to the red shift. So did the speed of light slow down? Or is the distance now proportionately further per the red shift "embiggement?" I vote for the second option.

Yup. Redshift indicates the light source is moving away from the observer. Moving away causes observed wavelength to increase, hence the visible spectrum is shifted toward the "red" end.

Standard physics. Wasn't this already discussed?