The Copernican principle

[__Ben__]

Why do we assume we're in a normal place in the universe, when we're on a planet in a solar system in a galaxy that supports life?

Isn't the vast majority of the universe the space between things?

Why is it we ignore the small scales when concluding the universe is isotropic and homogeneous. When anything that is applied to is true. A billard ball is apparently more uneven than the planet earth when enlarged to the same scale.

Isn't a typical place in the universe somewhere in a void between galaxies.

Isn't it also a place in the extreme distant future?

Edited January 28, 2022 by __Ben__
Typo

[bangstrom]

25 minutes ago, __Ben__ said:

Isn't a typical place in the universe somewhere in a void between galaxies.

Isn't it also a place in the extreme distant future?

Yes, the typical place is within a void.

Could you elaborate about the typical place being in the future?

Everything we observe in the vast majority the void is in our distant past. But, from the other end of the telescope, we are in the distant past from the perspective of the the void. Is that what you mean by the typical place being in our distant future?

[swansont]

1 hour ago, __Ben__ said:

Why is it we ignore the small scales when concluding the universe is isotropic and homogeneous. When anything that is applied to is true.

Is a tree homogeneous and isotropic? A human?

The universe is homogeneous and isotropic on a large scale. i.e. the scale used in astronomy and cosmology. Sometimes this is not explicitly declared, but often it is.

http://abyss.uoregon.edu/~js/cosmo/lectures/lec05.html (emphasis added)

"if the Universe is isotropic then this means you will see no difference in the structure of the Universe as you look in different directions. When viewed on the largest scales, the Universe looks the same to all observers and the Universe looks the same in all directions as viewed by a particular observer. Homogeneity, when viewed on the largest scales, means that the average density of matter is about the same in all places in the Universe and the Universe is fairly smooth on large scales."

 

[dimreepr]

5 hours ago, __Ben__ said:

Why do we assume we're in a normal place in the universe, when we're on a planet in a solar system in a galaxy that supports life?

Why do you assume you're human?

Edited January 28, 2022 by dimreepr

[__Ben__]

On 1/28/2022 at 11:28 PM, bangstrom said:

Could you elaborate about the typical place being in the future?

From what we currently know, the best evidence is that there's a finite point in the past (the big bang) and the Universe is open, so there's an infinite future. Therefore a typical place in the universe will be somewhere in the distant future.

 

On 1/29/2022 at 1:03 AM, swansont said:

Is a tree homogeneous and isotropic? A human?

The universe is homogeneous and isotropic on a large scale. i.e. the scale used in astronomy and cosmology. Sometimes this is not explicitly declared, but often it is.

http://abyss.uoregon.edu/~js/cosmo/lectures/lec05.html (emphasis added)

 

A human and a tree aren't homogeneous and isotropic, but a value of how isotropic and homogeneous could be given to them. A forest and a population would undoubtedly have a higher value for both.

Aren't we just forcing homogeneity and isotropy to fit with what we wish to be true by manipulating statistics?

How do you explain the cold spot in the wmap cmb? It just averages out over the whole so can be ignored?

https://en.m.wikipedia.org/wiki/CMB_cold_spot#:~:text=One possible explanation of the,us and the primordial CMB.&text=A 2015 study shows the,likely being associated with it.

 

[__Ben__]

"Due to isotropy, there is no `place' where the Big Bang occurred, there is no center point."

@swansont

Quote from the lecture you linked.

Is it wise to teach this concept in this manner? This is separating space from time. This becomes obvious once the concept of space-time is understood and counter to this there is very much a centre point in the past.

[swansont]

1 hour ago, __Ben__ said:

Aren't we just forcing homogeneity and isotropy to fit with what we wish to be true by manipulating statistics?

What’s being manipulated?

1 hour ago, __Ben__ said:

How do you explain the cold spot in the wmap cmb? It just averages out over the whole so can be ignored?

It’s a small deviation. A bump or divot on the billiard ball, so to speak. 

From your link:

The "Cold Spot" is approximately 70 µK (0.00007 K) colder than the average CMB temperature 

 

[__Ben__]

44 minutes ago, swansont said:

What’s being manipulated?

It’s a small deviation. A bump or divot on the billiard ball, so to speak. 

From your link:

The "Cold Spot" is approximately 70 µK (0.00007 K) colder than the average CMB temperature 

 

Yeah, "from the average cmb temperature", again using statistics in a way to dismiss the anisotropy. What is that in a percentage difference from the average?

After all the CMB is extremely cold isn't it?

Edited January 30, 2022 by __Ben__

[studiot]

1 hour ago, __Ben__ said:

Yeah, "from the average cmb temperature", again using statistics in a way to dismiss the anisotropy. What is that in a percentage difference from the average?

After all the CMB is extremely cold isn't it?

Rather than being quite so beligreant, why not do your own maths ?

I also recommend working in parts per million, not parts per hundred.

In that case the surface toughness of a billiard ball works out (quite coincidentally) as about the same as the variation in the CMB measurement.

70μK parts in 2,700,000μK is approximately 30 parts per million.

 

 

Quote

https://billiards.colostate.edu/faq/ball/smooth/

Since the radius of a pool ball is about 28560 microns, the “local” roughness observed is about 1/30000 or about roughly 30 parts per million. ... If you look just at the oceans, the roughness is around 150 feet in the worst swells, but that would be quite a bit smoother than the polished pool ball.

 

Edited January 30, 2022 by studiot

[__Ben__]

56 minutes ago, studiot said:

Rather than being quite so beligreant, why not do your own maths ?

70μK parts in 2,700,000μK is approximately 30 parts per million.

 

 

I'm here so you can do the math for me.

But I can do basic math and I just checked. You're out by a factor of 10. 

I get 257 parts per million.

Ok so that part of the Copernican principle seems to be OK.

What about the part that says we don't occupy a special place in the universe.

How many places are there that support life to ask the question?

Edited January 30, 2022 by __Ben__

[Genady]

1 hour ago, __Ben__ said:

What about the part that says we don't occupy a special place in the universe.

How many places are there that support life to ask the question?

What makes a place that supports life, special?

[studiot]

1 hour ago, __Ben__ said:

I'm here so you can do the math for me.

But I can do basic math and I just checked. You're out by a factor of 10. 

I get 257 parts per million.

Ok so that part of the Copernican principle seems to be OK.

What about the part that says we don't occupy a special place in the universe.

How many places are there that support life to ask the question?

Really ?

70 in 2.7 million

is

[math]\frac{{70}}{{2.7}}\;in\;\frac{{2.7}}{{2.7}}\;million[/math]

or

25.9 in 1 million

Which I think is close enough to 30 not to argue about.

[swansont]

6 hours ago, __Ben__ said:

Yeah, "from the average cmb temperature", again using statistics in a way to dismiss the anisotropy.

How so? You keep making these vague complaints that make no sense.

What would you compare a deviation to, if not the average?

5 hours ago, __Ben__ said:

But I can do basic math

Apparently not as well as you thought…

5 hours ago, __Ben__ said:

What about the part that says we don't occupy a special place in the universe.

How many places are there that support life to ask the question?

Life is part of biology and chemistry, not physics/cosmology. Unless you are arguing that life arose because our location in the cosmos, rather than the conditions on earth.

[Johnmo89]

On 1/28/2022 at 5:02 PM, __Ben__ said:

Why do we assume we're in a normal place in the universe, when we're on a planet in a solar system in a galaxy that supports life?

Isn't the vast majority of the universe the space between things?

Why is it we ignore the small scales when concluding the universe is isotropic and homogeneous. When anything that is applied to is true. A billard ball is apparently more uneven than the planet earth when enlarged to the same scale.

Isn't a typical place in the universe somewhere in a void between galaxies.

Isn't it also a place in the extreme distant future?

Interesting opinion. But why do you think that our planet is in some special place? Yes, there are optimal conditions for the origin of life, but don't you think that there could be thousands of such planets in the universe? So what makes our planet so special?