6 minutes ago, swansont said:

I wouldn’t.

It’s because my area is not cosmology, and not because you’ve not addressed points I’ve brought up, though it would be nice if you did, since “no soapboxing” is another rule we have

I did my best. I can see that's not enough for you, but I also think it would never be.

@swansont Our on-topic discussion had stopped on the temperature of hydrogen at the moment of recombination. Can you tell the radiation and matter energy densities right before and right after recombination? I'm also interested in the temperature of radiation right before recombination.

Edited December 28, 2025Dec 28 by Jacek

1 hour ago, Jacek said:

@swansont Our on-topic discussion had stopped on the temperature of hydrogen at the moment of recombination. Can you tell the radiation and matter energy densities right before and right after recombination? I'm also interested in the temperature of radiation right before recombination.

I'm not a cosmologist but I should have thought the temperature of the black body radiation from the Surface of Last Scattering could be worked out from the CMBR and the degree of cosmological redshift since then.

4 hours ago, Jacek said:

@swansont Our on-topic discussion had stopped on the temperature of hydrogen at the moment of recombination. Can you tell the radiation and matter energy densities right before and right after recombination? I'm also interested in the temperature of radiation right before recombination.

Then I guess you have some homework to do.

3 hours ago, exchemist said:

I'm not a cosmologist but I should have thought the temperature of the black body radiation from the Surface of Last Scattering could be worked out from the CMBR and the degree of cosmological redshift since then.

Yes, that’s ~3000 K. You can calculate it using the ionization energy of hydrogen and some other factors

16 minutes ago, swansont said:

Then I guess you have some homework to do.

Part of my homework should be yours, because you were asking me about the radiation before the CMB emission and I answered accordingly to my knowledge. Then you wrote about the reset of the thermal distribution by this emission, so I thought you should know basic parameter of this distribution.

25 minutes ago, swansont said:

Yes, that’s ~3000 K. You can calculate it using the ionization energy of hydrogen and some other factors

Are you saying that both the radiation right before recombination and hydrogen atoms at the moment of recombination were at 3000K? If that's the case, it wasn't reset.

Edited December 28, 2025Dec 28 by Jacek

1 hour ago, Jacek said:

Part of my homework should be yours, because you were asking me about the radiation before the CMB emission and I answered accordingly to my knowledge. Then you wrote about the reset of the thermal distribution by this emission, so I thought you should know basic parameter of this distribution.

Are you saying that both the radiation right before recombination and hydrogen atoms at the moment of recombination were at 3000K? If that's the case, it wasn't reset.

Reset? What do you mean by that?

1 minute ago, exchemist said:

Reset? What do you mean by that?

On 12/14/2025 at 4:24 PM, swansont said:

Recombination/ionization is not a thermal effect; the photons emitted would have a thermal variation reflecting the temperature of the (primarily) hydrogen at that time. But the energy levels do not have a thermal distribution. The nominal ionization energy is still 13.6 eV. That would “reset” any thermal distribution you might have beforehand.

@exchemist ask @swansont

8 minutes ago, exchemist said:

Reset? What do you mean by that?

You do not get a smooth curve of reduction in temperature over time - it’s like a phase transition; when water freezes or boils (or melts/condenses), the temperature is constant for a period of time while it’s happening.

IOW, recombination is not a thermal process. The 13.6 eV released is a quantized amount, rather than getting a thermal distribution.

2 hours ago, Jacek said:

Part of my homework should be yours, because you were asking me about the radiation before the CMB emission and I answered accordingly to my knowledge.

I think you misunderstand the situation. Nobody here owes you anything, and having an attitude that we do is off-putting. You have a hypothesis, so you are the one who needs to do the work.

2 hours ago, Jacek said:

Then you wrote about the reset of the thermal distribution by this emission, so I thought you should know basic parameter of this distribution.

I already mentioned it - the ionization energy of hydrogen is 13.6 eV.

2 hours ago, Jacek said:

Are you saying that both the radiation right before recombination and hydrogen atoms at the moment of recombination were at 3000K? If that's the case, it wasn't reset.

There is no “moment” of recombination. It did not happen all at once.

9 minutes ago, swansont said:

You do not get a smooth curve of reduction in temperature over time - it’s like a phase transition; when water freezes or boils (or melts/condenses), the temperature is constant for a period of time while it’s happening.

Was there non-smooth drop or increase in the radiation temperature, caused by recombination and the emission of CMB?

19 minutes ago, swansont said:

I already mentioned it - the ionization energy of hydrogen is 13.6 eV.

There is no “moment” of recombination. It did not happen all at once.

I was asking about the temperature of radiation before recombination.

23 minutes ago, swansont said:

I think you misunderstand the situation. Nobody here owes you anything, and having an attitude that we do is off-putting. You have a hypothesis, so you are the one who needs to do the work.

I think you still owe me moving this thread to your trash, don't you? Yes, our attitude is off-putting. I'm not kind to you, because you're a part of cancel culture for me.

Edited December 28, 2025Dec 28 by Jacek

1 hour ago, Jacek said:

I think you still owe me moving this thread to your trash, don't you?

Moderator Note

This is NOT discussing science.

You seem to have a big chip on your shoulder, so I have to assume you've been here before, under a different name, with the same lack of rigor and sour disposition, and failed to meet the requirements for the assertions you made. If you don't understand the criticisms your ideas spawn, please ask questions rather than lashing out or retaliating in non-science discussion forum ways. Civility greatly helps when trying to persuade others.

6 minutes ago, Phi for All said:

Moderator Note

This is NOT discussing science.

You seem to have a big chip on your shoulder, so I have to assume you've been here before, under a different name, with the same lack of rigor and sour disposition, and failed to meet the requirements for the assertions you made. If you don't understand the criticisms your ideas spawn, please ask questions rather than lashing out or retaliating in non-science discussion forum ways. Civility greatly helps when trying to persuade others.

Wrong assumption. Also, asking on-topic questions for @swansont is all I'm doing at the moment if you look above. As for you, you must be proud of this bold red font of yours, aren't you?

Edited December 28, 2025Dec 28 by Jacek

3 hours ago, Jacek said:

I think you still owe me moving this thread to your trash, don't you? Yes, our attitude is off-putting. I'm not kind to you, because you're a part of cancel culture for me.

The thread is not in the trash. Members cannot make posts there - those threads lock automatically. I explained why this was moved to speculations. IDGAF about any “cancel culture” nonsense - you’re complaining about having the forum rules applying to you, for which I have zero sympathy.

45 minutes ago, swansont said:

The thread is not in the trash. Members cannot make posts there - those threads lock automatically. I explained why this was moved to speculations. IDGAF about any “cancel culture” nonsense - you’re complaining about having the forum rules applying to you, for which I have zero sympathy.

Like I'm the one who cares about your sympathy... You apparently also DGAF (your choice of words - how civil) about on topic discussion, since you don't answer my questions regarding your statements. And you moved my thread from Astronomy and Cosmology to Speculations after 2 weeks and after my question and answer, what would be aging in the expanding universe without matter. And you still don't have your own answer to this question.

Edited December 28, 2025Dec 28 by Jacek

The short answer is that no one actually knows.

New discoveries happen all the time and the whole subject is under continual review.

BBC News

Dark Energy may be changing and with it the fate of the U...

A mysterious force called Dark Energy might be changing, in a way that challenges our current understanding of the nature of time and space.

Edited December 28, 2025Dec 28 by studiot

Is that what's called 'cancel culture' these days ?
When someone points out the mistakes in your thinking ?
Get over yourself !!!

The universe's temperature is slowly decreasing as it expands.
At some point, the universe was cool enough for electrons to combine with protons to form Hydrogen atoms, and not get immediately kicked away because the temperature can no longer supply the 13.6 eV ionization energy.
As this was happening over a period of time*, the universe's temperature stops decreasing, and plateaus, as each electron capture releases 13.6 eV into the environment. this, as Swansont explained, is why water stays at 100^o, while boiling, or 0^o, while freezing, until there is no more water.

Does your arrogance and persecution complex make you think you can do complex Cosmology when you don't understand simple phase changes.

• - If it happened all at once, the CMB would be one temperature, and not 'lumpy' to a few parts per million.
  ( if you want to impress us, try to calculate duration of the recombination era, using the anisotropies of the CMB, and the expansion of the universe at the time )

7 minutes ago, MigL said:

Is that what's called 'cancel culture' these days ?
When someone points out the mistakes in your thinking ?
Get over yourself !!!

So the more exclamation marks, the more right you are and the more errors in my thinking? I don't argue when I'm wrong, like in case of recombination not happening all at once.

That's what I call cancel culture: https://www.scienceforums.net/topic/140238-cancel-culture-in-major-astronomy-communities/

14 minutes ago, MigL said:

Does your arrogance and persecution complex make you think you can do complex Cosmology when you don't understand simple phase changes.

• - If it happened all at once, the CMB would be one temperature, and not 'lumpy' to a few parts per million.
  ( if you want to impress us, try to calculate duration of the recombination era, using the anisotropies of the CMB, and the expansion of the universe at the time )

Again, I don't argue when I'm wrong, and your criticism based on my assumed misunderstanding of simple phase transition is one of the nastiest I've ever read. Congratulations.

Please, find someone else to impress you, ok? Or impress yourself by this calculation.

No wonder you have 40 pages of banned/suspended users. Think for a second about your own attitude and your own choice of words.

Edited December 28, 2025Dec 28 by Jacek

Im curious given that conformal time is the total comoving distance light could have travelled. Why you would feel this better defines the age of the Universe?

If you look at the curvature of the accelerating rate of expansion from our location to the radius of the observable universe as well as the detail that conformal time is unit less. This would mean your seconds will change in duration from one second to the next.

Whereas proper time this isn't the case except for time dilation effects however that's accounted for in the look back time to determine the age of the universe.

Try this thought experiment let's say light has already traveled one light year. Now add expansion. The region light has already traveled is expanding as well as the distance to the observer ahead of the beam. This is occurring every second by the Hubble constant value

So ask yourself this why would this be a better representation for age ?

Particularly given that the Hubble constant varies over time

---

Edited December 29, 2025Dec 29 by Mordred

@Mordred as far as I can tell, conformal time η=∫dη=∫dt/a(t)=47Gy is in billion years, so it's not dimensionless.

I totally agree that a tick of material clock remains constant, while a tick of radiation extends with its period due to the expansion.

Before I answer your question why would it be a better representation for the age of a universe, I'm asking you to answer my preliminary question: What would be aging and how in the expanding universe without matter?

Edited December 29, 2025Dec 29 by Jacek

matter isnt the only factor when it comes to expansion as matter is strictly fermionic particles. You also have the cosmological constant as well as radiation such as photons that contribute to expansion.

unless you universe is completely empty if so then can you consider it as a universe ?

Universe from my preliminary question is filled with radiation. If you want, you can also have dark energy, but no dark matter, no baryonic matter and no other massive particles.

Edited December 29, 2025Dec 29 by Jacek

either way my question remains even if you apply a radiation only solution to the FLRW metric radiation still causes expansion. Barbera Ryden's introductory to cosmology will give you the look back times for single component universe. If you apply a single component universe your expansion rates will differ significatly and you would not get 47 Gy for your conformal time as matter contributes to expansion. The expansion contributors are matter, radiation lambda and curvature terms though for our close to flat universe curvature can be safely ignored.

So the conformal time you have would be incorrect as you did not calculate the expansion rate for a universe with no matter.

Your question was answered in my preliminary question, because I was asking about the EXPANDING universe without matter.

Expansion rate is (da/dt)/a, so it's based on the scale factor as a function of time, so the conformal time calculation ∫dt/a(t) definitely takes it into account. If you want, we can change it to ∫dz/H(z) and the result will be the same.

you do understand that a radiation only universe would not expand at the same rate as a multi component universe do you not ? That would effect your scale factor

\[H_z=H_o\sqrt{\Omega_m(1+z)^3+\Omega_{r}(1+z)^4+\Omega_{\Lambda}}\]

Edited December 29, 2025Dec 29 by Mordred

Yes, I do. I also know a useful solution of the Friedmann equations for the radiation dominated universe. It would be other scale factor function of time, but it would still be explicit.

So @Mordred can you finally answer my preliminary question?

Edited December 29, 2025Dec 29 by Jacek

do yourself a favor calculate the look back time for a radiation only universe. You will not get 47 Gyrs. Nor will you get 13.8 Gyrs

I've given you a source material to see what I mean

Edited December 29, 2025Dec 29 by Mordred