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The science law is very clearhttps://www.answers.com/Q/Why_does_the_intensity_decrease_with_the_square_of_the_distance_from_a_point_sourceWhy does the intensity decrease with the square of the distance from a point source?Intensity of light is defined as energy per unit area. As we move away from the light point source, the area over which the energy of light distributes is generally spherical or hemispherical. The area of a sphere or hemisphere increases proportional to the square of radius, where the radius in this case is the distance from the point source. Thus Intensity of light, which is inversely proportional to area, decreases with the square of distance.

Thanks for the explanation about the dark energy, although in the article they don't say anything about "radiation".

But if your Universe is evolving in shape and size over time — which our expanding Universe consisting of radiation, matter, and dark energy most definitely is — you have to take that into account as well.

In any case, I would like to focus on your following explanation:

Well, I can agree that if a galaxy is closer, (not further away) than it should appear bigger.

However, I still don't understand why if it was closer 13BY ago, but due to the expansion its emitted photons of light had to cross very long distance (13BLY) than it also should appear bigger?

The science law is very clearhttps://www.answers.com/Q/Why_does_the_intensity_decrease_with_the_square_of_the_distance_from_a_point_sourceWhy does the intensity decrease with the square of the distance from a point source?

Intensity of light is defined as energy per unit area.

So, we must understand the total distance that the emitted photon of light from that galaxy had to cross over time.

Don't you agree that if the photon of light from this galaxy that 13 BY ago was located next to us, had to cross a distance of 13 BLY than it should appear much smaller today?

With regards to the space - time diagram that you have offered:This diagram represents only the observable universe of about 46BLY.

So, don't you agree that the space time diagram for a bigger universe (or even infinite Universe) should be quite different from this diagram?

QuoteSo, we must understand the total distance that the emitted photon of light from that galaxy had to cross over time.It is very dependent on how that distance is measured, so there's no meaningful answer to this without that definition. I defined the distance between here and where the light was emitted as proper distance in the comoving coordinate system (scaled for normal distance and time) as per my linked graph in post 396. The distance is marked off at the bottom of the chart. Where (or how long) the light traveled between here and there is irrelevant to the apparent size of the galaxy since the apparent size is not a function of either of those things, and where that galaxy is 'now' is also irrelevant since I'm not looking at light from where it is now, and yet it is on this that you choose to focus, having this naive intuition that we see things where they are now because that is a good approximation when you're looking at a tree.

I defined the distance between here and where the light was emitted as proper distance in the comoving coordinate system (scaled for normal distance and time) as per my linked graph in post 396.

QuoteQuoteDon't you agree that if the photon of light from this galaxy that 13 BY ago was located next to us, had to cross a distance of 13 BLY than it should appear much smaller today?You ignore the logic that shows this to result in a contradiction.

QuoteDon't you agree that if the photon of light from this galaxy that 13 BY ago was located next to us, had to cross a distance of 13 BLY than it should appear much smaller today?

QuoteHowever, I still don't understand why if it was closer 13BY ago, but due to the expansion its emitted photons of light had to cross very long distance (13BLY) than it also should appear bigger?The distance the light travels is pretty meaningless without an exact specification of how that distance is measured. Point is, that light was emitted from fairly close by, and the apparent size of the object can be directly computed from that without consideration of how much time it takes. When I compute the apparent size (in arseconds) of the moon, I don't need to worry about how long light takes to make the trip or if the moon has moved somewhere else while the light was getting here. It is simple trigonometry.

Point is, that light was emitted from fairly close by

and the apparent size of the object can be directly computed from that without consideration of how much time it takes.

When I compute the apparent size (in arseconds) of the moon, I don't need to worry about how long light takes to make the trip or if the moon has moved somewhere else while the light was getting here. It is simple trigonometry.

There is no fiber optics in the open space.

Let's take real example about the Farthest Known Galaxy in the Universe Discovered:https://www.space.com/18502-farthest-galaxy-discovery-hubble-photos.html

"The new record holder is the galaxy MACS0647-JD, which is about 13.3 billion light-years away."

So, in one side we see a galaxy (let's call it galaxy A) at a distance of 13.3 BLY, while on the other side there is other galaxy (galaxy B) at a similar distance from us.Therefore, we can assume that the distance between galaxy A to galaxy B could be 26.6 BLY.

We all know that the size of the whole Universe after the inflation was only 10,000 LY.

We also know that it took almost 380 Million years for the atoms to be formed after the Big bang.

Let's assume that the Milky Way was there at a distance of 50,000LY away from galaxy A (420 Million years after the BB).If I understand you correctly, that distance represents the proper distance.

We clearly know that the light travels at the speed of light. (With or without the impact of the expansion)

Due to the compact size of the early Universe (at the age of 420 MY) it is clear that the impact of the expansion rate at this compact early universe is quite neglected. (74 Km//s per 3MLY). Therefore, the light from galaxy A should cross a distance of 50,000LY in about 50,000 Year.

So, why it took the light from galaxy A so long time (13.3BY) to get to the Milky Way?

Can you please explain how the proper/commoving distance velocity could force the light to travel 13.3 BLY in order to cross a proper distance of only 50,000

So the light was emitted from a distance of 50,000LY (that was the distance between the Milky way to galaxy A when the universe was 420My old). Proper distance. This is very clear.

Quote from: Halcand the apparent size of the object can be directly computed from that without consideration of how much time it takes. Why is it? This is totally unclear to me.

I still don't understand why the proper distance can set any sort of impact?

From our point of view we see a galaxy at a distance of 13.3 BLY that its light had traveled for 13.3 BY to get to our earth. With or without the expansion, the total distance is fixed and the total time is fixed.

It should take the moon light about 1.5 sec to get to earth.Let's assume that somehow we can use the expansion process to move the moon away from us so fast that the next time that we get its light is after it gets to a distance of 1LY away and 1Y from now.

Here's a link concerning why light-travel distance shouldn't be used:http://www.astro.ucla.edu/~wright/Dltt_is_Dumb.html

QuoteSo, in one side we see a galaxy (let's call it galaxy A) at a distance of 13.3 BLY, while on the other side there is other galaxy (galaxy B) at a similar distance from us.Therefore, we can assume that the distance between galaxy A to galaxy B could be 26.6 BLY.Using light travel distance, yes.

QuoteWe all know that the size of the whole Universe after the inflation was only 10,000 LY.Reference please. I'm not buying that one.

Perhaps your example could be real one like MACS0647-JD which was much further away than 50,000 LY at age 420 MY. More like 3 billion LY away, according to the limited resolution of my picture. That event is on our current light cone.

You make it sound like the moon blinks off, and then on again when it's completely somewhere else.Your numbers are unreasonable. If expansion is that severe, the universe would be 1.5 seconds old, and there would be nothing to see at all.

Think about it instead of just dismissing it because you already know a different answer.

In this article it is stated:" This has one simple property: the distance in light years is never greater than the age of the Universe in years, avoiding at least one appearance of speeds greater than the speed of light."However, you have just confirmed that the distance between two galaxies based on light travel distance is 26.6 BLY

"The redshift z is usually the only number in the whole story that is unambiguous and likely to be correct."

we can easily calculate the distance from a shift in a sound:"If an SR-71 blackbird flies over at Mach 3 and you hear the sound 30 seconds later, then answer to the question "How far away is it?" is clearly not 30 "sound seconds" or 10 km."

They also add "The Universe is homogeneous and isotropic, so it has no edge. Thus there cannot be a maximum distance."Therefore, without an edge and in order to meet the requirement to homogeneous and isotropic it actually must be infinite or at least very, very big. Much bigger than that 92BLY.

In the article it is even stated that by using the redshift for light travel time distance we get disagrees with the Hubble law...Hence, if it generally disagrees with the Hubble law than they have to understand that there is a problem with Hubble law (not with the redshift!!!)

As we discuss about a redsfit, I also see other sever contradiction between the redshift and the BBT:Based on this article we can calculate the light travel time based on the redshifthttp://www.astro.ucla.edu/~wright/CosmoCalc.htmlSo, if the redshift is 6 than: The age at redshift z was 0.942 Gyr.The light travel time was 12.779 Gyr.If the redshift is 12The age at redshift z was 0.372 Gyr.The light travel time was 13.349 Gyr.So, we can claim that we see the light from two galaxies at the early Universe.One at the age of 0.942 Gyr while the other at the age of 0.372 Gyr.Based on the BBT, at that time the universe was quite compact and small.Therefore, those galaxies were located quite nearby.However, the difference in their redshift is 12-6 =6.So, two nearby galaxies in the early universe have already so severe difference in their redshift.

However, based on this calculation we know that the meaning of redshift 6 is:The light travel time was 12.779 Gyr.Therefore, if about 13BLY we could stand in one galaxy and monitor the redshift from the other nearby galaxy, we could find that we get a redshift of 6 which equivalent to light travel time of 12.779 Gyr.

So, how could it be that in a maximal early universe age of only one billion years, we could have a light travel time of 12.779 Gyr between two nearby galaxies?

QuoteWe all know that the size of the whole Universe after the inflation was only 10,000 LY.[physicsforums]:"It is very difficult to quantify the size of the observable universe after inflation ended."

You claim that the size of the universe at age 420MY should be 3BLY.

Actually, if we increase the early universe at the speed of light, it should get to about 420MLY.Therefore, in total we need to increase its size at 10 times the speed of light in order to get a 3BLY universe after 420MY.

What about the momentum?

If due to the expansion/inflation we get that kind of size increasing (10 times the speed of light), why it suddenly slow down?

Theoretically, if something is moving away from us faster than the speed of light, while the momentum law is very clear, than how can we ever see again its light?

How can we get any sort of star while the expansion rate is so high at the early universe?

How the gravity could work under those ultra high forces.

Do you agree that when the Universe was very compact and very dense, its internal gravity was maximal?Why the gravity at that time couldn't prevent the expansion + inflation process?

I really try to understand how the BBT works. I'm ready to accept any answer.

Don't you think that as "The redshift z is usually the only number in the whole story that is unambiguous and likely to be correct" than we should fix our theories to meet this redshift instead of the other way?