Need help understanding the illusion of the early universe that surrounds us?

[TakenItSeriously]

Imagine we look in one direction and see a galaxy 10 billion years away. Then we look in the opposite direction and see a different galaxy 10 billion years away It appears like they are 20 billion light years apart and we are directly inbetween these two galaxies from 10 billion years ago and the CMB looks like a big sphere of 27BLY diameter where we are at the center.

 

I understand this must be an illusion of spacetime. As a child I used to think it was because spacetime must be curved like a sphere and we were looking around all sides of the sphere to the other side. This was back when closed space was defined a cyclicle universe and not a sphere.

 

But since science has popped my bubble with a flat universe. I no longer know how to understand this illusion of an inside out universe.

 

Can someone please explain this illusion. I know that the universe is expanding.

Edited June 25, 2016 by TakenItSeriously

[Sensei]

Regardless of direction in which we look, we see galaxies in early stage of their life.

[Strange]

It is not an illusion. You can look in any direction and see galaxies some of which will be about 13 billion light years away. Or the CMB which is 13.8 billion light years away.

 

Actually, that's not quite true. The light has taken 13 billion light years to get here. But when it was emitted, those galaxies were about 4 billion light years away. Now they are about 45 billion light years away.

[TakenItSeriously]

It is not an illusion. You can look in any direction and see galaxies some of which will be about 13 billion light years away. Or the CMB which is 13.8 billion light years away.

 

Actually, that's not quite true. The light has taken 13 billion light years to get here. But when it was emitted, those galaxies were about 4 billion light years away. Now they are about 45 billion light years away.

If its not an illusion then the size of the universe 13.7 Billion years ago during the CMB phase would have had a diameter of 27 billion light years since it completely surrounds our observable universe which can't be true.

[Mordred]

Incorrect. You can see light from further than the age of the universe. This is due to expansion.

 

This is tricky for many to understand how light can reach us at distances greater than the age of the universe.

 

What happens is that the light has already travelled part of the way. Yet during the light path the distances on the path already travelled and ahead of the light path continues to expand. Locally though that expansion per Mpc is miniscule so light will continue to make headway.

 

The observable universe is significantly larger than 13.7 Gly in radius.

 

This expansion affects the light path wavelength causing cosmological redshift

Edited June 26, 2016 by Mordred

[TakenItSeriously]

Incorrect. You can see light from further than the age of the universe. This is due to expansion.

This is tricky for many to understand how light can reach us at distances greater than the age of the universe.

What happens is that the light has already travelled part of the way. Yet during the light path the distances on the path already travelled and ahead of the light path continues to expand. Locally though that expansion per Mpc is miniscule so light will continue to make headway.

The observable universe is significantly larger than 13.7 Gly in radius.

This expansion affects the light path wavelength causing cosmological redshift

Ok but my point is that we are seeing those distant objects as they existed billions of years ago right? Yet the universe seems to be larger back then because those objects that surround us are further away.

 

Let me try this example. We create imaginary concentric spheres with us at the center every billion light years. Then we see the universe as it existed back in time a billion years ago, 2 billion years ago,...,and finally the CMB surrounds everything we can see. 13.7 billion years ago.

 

With every billion years we look back in time the universe appears to be larger, not smaller.

 

I assume this is an illusion of spacetime because we know the further back we go the smaller the universe should be.

Edited June 26, 2016 by TakenItSeriously

[Mordred]

No in actuality we can calculate the proper distance when the object first started emitting light and the proper distance today of any stellar object.

 

Granted the distance today requires assumptions that nothing out of the ordinary occured.

 

The universe doesnt appear larger in the past. You can't see an edge of the observable universe at any point in time.

 

That isnt how it works. The furthest back we can see is shortly after the dark ages at the surface of last scattering. That CMB surrounds us today.

 

No matter which direction you look in or how far you look you will see the universe around you. Your merely at the center of the observable universe due to your current location.

 

You never have a god like view of the full universe in a particular direction as were inside the universe.

 

You can only calculate the size of that observable portion based upon observation and redshift data with other methods such as the Sache Wolfe effect and stellar parallax. With that data we extrapolate the proper distances. The FLRW metric initially uses commoving distances ( in the past we used conformal distances prior to the cosmological constant).

 

These in turn allow to calculate the proper distance then and today.

 

The calculator in my signature does precisely that.

 

As far as the observable universe it will always be a sphere. When they state the universe is flat. They are not describing its shape. They are describing its actual density compared to its critical density.

 

This is in actuality a thermodynamic relationship that affects light paths. A perfectly flat universe without the cosmological constant is one that is static. Yet this is in itself unstable.

 

Our universe is extremely close to flat with a cosmological constant so will continue to expand.

 

I suggest reading these two articles I wrote a few years back they will help.

 

http://cosmology101.wikidot.com/redshift-and-expansion

http://cosmology101.wikidot.com/universe-geometry

 

Page two of the last article details the Flrw metric and how curvature affects light paths (in effect the null geodesics on a universal scale GR)

Here is page two on the geometry article.

 

http://cosmology101.wikidot.com/geometry-flrw-metric/

 

I broke this section down to the 2d 3d and 4d metrics on all three curvatures. Positive,negative and flat cosmologies. The formulas on this page is the calculations for commoving distances.

Edited June 26, 2016 by Mordred

[TakenItSeriously]

No in actuality we can calculate the proper distance when the object first started emitting light and the proper distance today of any stellar object.

Granted the distance today requires assumptions that nothing out of the ordinary occured.

The universe doesnt appear larger in the past. You can't see an edge of the observable universe at any point in time.

That isnt how it works. The furthest back we can see is shortly after the dark ages at the surface of last scattering. That CMB surrounds us today.

No matter which direction you look in or how far you look you will see the universe around you. Your merely at the center of the observable universe due to your current location.

You never have a god like view of the full universe in a particular direction as were inside the universe.

You can only calculate the size of that observable portion based upon observation and redshift data with other methods such as the Sache Wolfe effect and stellar parallax. With that data we extrapolate the proper distances. The FLRW metric initially uses commoving distances ( in the past we used conformal distances prior to the cosmological constant).

These in turn allow to calculate the proper distance then and today.

The calculator in my signature does precisely that.

As far as the observable universe it will always be a sphere. When they state the universe is flat. They are not describing its shape. They are describing its actual density compared to its critical density.

This is in actuality a thermodynamic relationship that affects light paths. A perfectly flat universe without the cosmological constant is one that is static. Yet this is in itself unstable.

Our universe is extremely close to flat with a cosmological constant so will continue to expand.

I suggest reading these two articles I wrote a few years back they will help.http://cosmology101.wikidot.com/redshift-and-expansionhttp://cosmology101.wikidot.com/universe-geometry

Page two of the last article details the Flrw metric and how curvature affects light paths (in effect the null geodesics on a universal scale GR)

Here is page two on the geometry article.http://cosmology101.wikidot.com/geometry-flrw-metric/

I broke this section down to the 2d 3d and 4d metrics on all three curvatures. Positive,negative and flat cosmologies. The formulas on this page is the calculations for commoving distances.

I think I figured it out.

I realized we had to be on different pages which was my fault.

 

I had assumed we knew the size of the early universe. Specifically the age and the global size at the CMB state, which, I assumed to be the reference state for projecting lookback events into the proper time and proper distance.

 

Then I realised, that cant be logically true because we don't know if the universe is infinite.

 

Thus making my line of reasoning for comparring CMB global size totally invalid.

 

So now Im assuming the datum data is the density and time at CMB. Is this correct?

Edited June 26, 2016 by TakenItSeriously

[Mordred]

Yes density data is a vital piece of information. We can utilize the ideal gas laws to help determine the density at a particular time period via the average blackhody temperature at that time period.

 

That being said there are other supportive pieces of data that are also involved.

 

One being tbe cosmological redshift. The problem with using redshift however is knowing the emitter frequency. Without a known emitter frequency we cannot calculate the amount of redshift.

 

Thankfully various elements such as the most abundant element hydrogen has unique spectral frequency bands. We have excellent data on using spectronomy on all known element's and can readily identify those elements via spectrography.

 

The frequency bands will be redshifted when looking at those elements at far distances.

 

Another tool is luminosity to mass relations. (Formula in the luminosity section on the redshift article)

 

Unfortunately no single method is usable to determine distance. Through considerable experimentation and research scientists today have numerous tools that work extremely well to fine tuning distance measures.

 

These are under the category the Cosmic distance ladder.

 

This wiki link has a decent coverage

https://en.m.wikipedia.org/wiki/Cosmic_distance_ladder

Edited June 26, 2016 by Mordred