I LightCone Calculator Improvements

[Jorrie]

This is as expected. See my post #26. Either Ω_m,0 or Ω_Lambda,0 has to give if we want to keep Omega_T,0=1.

 

[pbuk]

Yes, if you got to your repo at https://github.com/burtjordaan/light-cone-calc.github.io and select Settings -> Pages, then make it look like this:
View attachment 305226
You should then (after a short delay to build it) see your version of the site at https://burtjordaan.github.io/light-cone-calc.github.io

Note that with the current settings @Jorrie's development fork is served at https://burtjordaan.github.io/light-cone-calc.github.io/docs/.

 

[Jorrie]

Note that with the current settings @Jorrie's development fork is served at https://burtjordaan.github.io/light-cone-calc.github.io/docs/.

Thanks for providing the runable link, because I still have finger trouble with Github. Note that this is not the latest version, which JimJCW (somehow) got hold of, albeit with the actual OutputCSV.js missing - Github seems to be a difficult animal to understand at my age...

 

[JimJCW]

Note that this is not the latest version, which JimJCW (somehow) got hold of, ...

I got it from Post #7: https://light-cone-calc.github.io/

 

[JimJCW]

This is as expected. See my post #26. Either Ω_m,0 or Ω_Lambda,0 has to give if we want to keep Omega_T,0=1.

I think if at input Ω_m,0 = 0.3111 but at output it becomes Ω_m,0 = 0.3110082030, it is a discrepancy.

ICRAR, in this situation, gives,

The space will not be flat in this case.

 

[Jorrie]

I think if at input Ω_m,0 = 0.3111 but at output it becomes Ω_m,0 = 0.3110082030, it is a discrepancy.

You are right, but to output Omega_T,0 >1 would also be a discrepancy, because without giving the value explicitly, the collaboration the spatial flatness in words, if I read the paper correctly.
So maybe we miss something in the equations, but as a non-cosmologist, I can't figure out what.
Our previous versions of Lightcone8 suffered the same problem.

I'm also still perplexed as to why the Trial Version does not have CSV output option working when selected. I did upload it with the OuputCSV.js file (a new file that was not there is earlier versions) and it shows on my fork.

 

[Jorrie]

I'm also still perplexed as to why the Trial Version does not have CSV output option working when selected. I did upload it with the OuputCSV.js file (a new file that was not there is earlier versions) and it shows on my fork.

Ok, found error for CSV output and fixed it.
Should now work on http://jorrie.epizy.com/docs/index.html

 

[Jorrie]

Ok, found error for CSV output and fixed it.
Should now work on http://jorrie.epizy.com/docs/index.html

@pbuk , I think the trial version is now at the top of your branch as well(?)
I think we should keep the pre-input-reconfigure at the top of your branch until we have consensus on which way to go.

 

[pbuk]

You are right, but to output Omega_T,0 >1 would also be a discrepancy, because without giving the value explicitly, the collaboration the spatial flatness in words, if I read the paper correctly.
So maybe we miss something in the equations, but as a non-cosmologist, I can't figure out what.

Yes I agree, if we want curvature then I think this must be input explicitly as it is in LightCone7 and 8. I'm not a cosmologist either, but I don't think we are missing anything, we just have to deal as modellers with the fact that our inputs are uncertain. The objective in creating any physical model is not to faithfully reproduce inputs, it is to create an output that is the best fit to the observations. With this in mind I plan to do some investigation on how best to 'spread' the Ω_rad,0 adjustment to achieve the best fit to t₀ (age).

I think if at input Ω_m,0 = 0.3111 but at output it becomes Ω_m,0 = 0.3110082030, it is a discrepancy.

But I think the alternative which is to have an input of Ω₀ = 1 become an output of Ω₀ = 0.9999101295 is worse: non-zero curvature is "a big thing" and is something that should be explicitly input, not extracted out of what is more or less rounding errors.

I'm also still perplexed as to why the Trial Version does not have CSV output option working when selected. I did upload it with the OuputCSV.js file (a new file that was not there is earlier versions) and it shows on my fork.

I think this may have got lost when I imported from your fork - because I can't create pull requests from your fork I had to clone it and copy files over: I picked up the changed files but must have missed the addition.

 

[JimJCW]

You are right, but to output Omega_T,0 >1 would also be a discrepancy, because without giving the value explicitly, the collaboration the spatial flatness in words, if I read the paper correctly.
So maybe we miss something in the equations, but as a non-cosmologist, I can't figure out what.
Our previous versions of Lightcone8 suffered the same problem.

Let’s use PLANCK(2018+BAO) as an example for the following discussion (see Post #25):

If we insist to have,

we are forced to have,

So, Ω₀ cannot be 1 in this case.

If we set ‘Total density parameter, Ω’ in LightCone8.1.2 - Jorrie to be 1.000091824, the discrepancy is eliminated:

To summarize:

We cannot insist that Ω_Λ,0 + Ω_m,0 =1 as is done in Planck 2018 results. I and still have Ω₀ = 1.​

​

@pbuk

 

[pbuk]

We cannot insist that Ω_Λ,0 + Ω_m,0 =1 as is done in Planck 2018 results. I and still have Ω₀ = 1.​

This is not correct. Planck 2018+BAO gives us $\Omega_{m,0} = 0.3111 \pm 0.0056; \Omega_{\Lambda,0} = 0.6889 \pm 0.0056$. Now we can argue about the independence of those errors, but they certainly don't give us $\Omega_{m,0} + \Omega_{\Lambda,0} = 1.00000 000 \pm 0.00000 000$. Adjusting $\Omega_{m,0}$ to 0.311008176 to accommodate $\Omega_{rad,0}$ is still within $0.02 \sigma$ of the survey result!

Let's look at the values at $t = t_0$as they are now with Planck 2018+BAO selected, and with $\Omega_{m,0}$ forced to 0.3111

Parameter	Planck 2018+BAO	LightCone8 default	Forced $\Omega_{m,0}$
$\Omega_{\Lambda,0}$	0.6889±0.0056	0.6889000000	0.6889000000
$\Omega_{m,0}$	0.3111±0.0056	0.3110082030	0.3111000000
$\Omega_{rad,0}$	~9.180e-5	0.00009179699026	0.00009182408501
$\Omega_{0}$	"Consistent with 1"	1.000000000	1.000091824
$\Omega_{\kappa,0}$	"Consistent with 0"	0.000000000	0.00009182408501
Age	13.787±0.020 Gyr	13.78704250 Gyr	13.78629120 Gyr

Now OK, it doesn't make a huge amount of difference (except to curvature itself of course), but LightCone8 as it is gets the age of the Universe bang in the middle of the Planck 2018+BAO result whereas if you allow positive curvature it is 1 out in the 5th significant figure. This is not the point though, the Planck 2018 results are fitted with the assumption of flatness so it is inconsistent to use the numbers to say there is curvature.

 

[JimJCW]

This is not correct. Planck 2018+BAO gives us $\Omega_{m,0} = 0.3111 \pm 0.0056; \Omega_{\Lambda,0} = 0.6889 \pm 0.0056$. Now we can argue about the independence of those errors, but they certainly don't give us $\Omega_{m,0} + \Omega_{\Lambda,0} = 1.00000 000 \pm 0.00000 000$. Adjusting $\Omega_{m,0}$ to 0.311008176 to accommodate $\Omega_{rad,0}$ is still within $0.02 \sigma$ of the survey result!

I think LightCone8 is working properly. We can use it to verify the following table:

It suggests we cannot insist that Ω_Λ,0 + Ω_m,0 =1 and still have Ω₀ = 1 and Ω_k = 0.

We may be able to use statistical argument to say that Ω₀ is approximately equal to 1 for a particular observation data, but it is not.

 

[Jorrie]

So what is the consensus: do we declare Lightcone8 with the trail UI interface as good enough, meaning we take away the "Jorrie Trial UI" in the title, or do we wait for a cosmologist to advise us?

My opinion is that as an educational tool, it is as good as it needs to be.

 

[JimJCW]

So what is the consensus: do we declare Lightcone8 with the trail UI interface as good enough, meaning we take away the "Jorrie Trial UI" in the title, or do we wait for a cosmologist to advise us?

My opinion is that as an educational tool, it is as good as it needs to be.

I am confused. Currently I am looking at two versions:

LightCone8: https://burtjordaan.github.io/light-cone-calc.github.io/
LightCone8.1.2 - Jorrie Trial UI: https://light-cone-calc.github.io/

Which one are we talking about? Do you mean replacing LightCone8 with LightCone8.1.2 - Jorrie Trial UI?

@pbuk

 

[Jorrie]

Yes, that the trail becomes the "official model", provided that we agree that we should input these 5 parameters, all givens by the Planck collaboration.

Our model implementation then forces $\Omega$ to be whatever this input is (default 1, but we are allowed to change this for educational purposes).^(a) This is done by subtracting $\Omega_R$ from $\Omega_M$.
Or we can decide to go more sophisticated by using a statistical method, based on the given error bars on all the inputs. My suggestion is that the "trail version" is good enough for now.

Footnote (a). When we started the original project, the then-core members were keen to keep options open so that hypothetical open and closed models could be demonstrated. Plus of course to be ready for potential future observation favoring a universe that is not spatially flat.

 

[JimJCW]

Yes, that the trail becomes the "official model", provided that we agree that we should input these 5 parameters, all givens by the Planck collaboration.

View attachment 305433
Our model implementation then forces $\Omega$ to be whatever this input is (default 1, but we are allowed to change this for educational purposes).^(a) This is done by subtracting $\Omega_R$ from $\Omega_M$.

I am still concerned with the discrepancy that at input, Ω_m,0 = Matter density parameter, Ω_M = 0.3111, but at output, Ω_m,0 = OmegaM = 0.311008203. Some people may consider it as an error in the calculator.

What will happen to ‘LightCone8: https://burtjordaan.github.io/light-cone-calc.github.io/’? Will it be still available?

I think one should not take numbers in Planck 2018 results. I inflexibly. Using Planck + BAO as an example, it gives,

They do not add up to Ω₀ = Ω_Λ,0 + Ω_m,0 + Ω_R,0 =1 and are, therefore, not consistent with LightCone 8 Tutorial Part III – How Things are Computed,

The Ω without subscript represents the present overall density parameter: Ω=Ω_Λ+Ω_m+Ω_r, which adds up to unity in the case of flat space.​

@pbuk

 

[Jorrie]

What will happen to ‘LightCone8: https://burtjordaan.github.io/light-cone-calc.github.io/’? Will it be still available?

I don't think so, because it gives exactly the same "error", if we can call it that. It likewise reduces Ω_m,0 to 0.3110 in order to keep Ω₀ =1. So no benefit in keeping it, AFAICS.

I tend to agree with @pbuk that it is preferable to "err" in $\Omega_{m,0}$, rather than allowing Lightcone8 to output a non-unity Ω₀. Maybe we should reduce both $\Omega_{m,0}$ and $\Omega_{\Lambda,0}$ proportionally.
We can easily explain the discrepancies in the UI.

Do you think we should use the Planck + BAO as initial default? I used the second last column, because the collaboration calls it their "base data".

 

[JimJCW]

I don't think so, because it gives exactly the same "error", if we can call it that. It likewise reduces Ω_m,0 to 0.3110 in order to keep Ω₀ =1. So no benefit in keeping it, AFAICS.

I tend to agree with @pbuk that it is preferable to "err" in $\Omega_{m,0}$, rather than allowing Lightcone8 to output a non-unity Ω₀. Maybe we should reduce both $\Omega_{m,0}$ and $\Omega_{\Lambda,0}$ proportionally.
We can easily explain the discrepancies in the UI.

I believe LightCone8 (https://burtjordaan.github.io/light-cone-calc.github.io/) is functioning properly. Its results are consistent with those of ICRAR (see Post #22) and its calculated Ω’s can be verified with equations in LightCone 8 Tutorial Part III – How Things are Computed (see Post #148 of the thread A glitch in Jorrie’s Cosmo-Calculator?). I think at least this version should be kept as an option.

I think the discrepancy in LightCone8.1.2 - Jorrie Trial UI (https://light-cone-calc.github.io/) (see Post #46) is caused by a mathematical error. The calculator is requiring the following two equations to be valid at the same time in a flat space, but this is impossible:

Ω_Λ,0 + Ω_m,0 = 1​

Ω_Λ,0 + Ω_m,0 + Ω_R,0 = 1​

The origin of the above problem can be traced to Planck 2018 results. I. We shouldn’t use the numbers in it inflexibly. Using Planck + BAO as an example, it gives,

They do not add up to Ω₀ = Ω_Λ,0 + Ω_m,0 + Ω_R,0 =1 and are, therefore, not consistent with LightCone 8 Tutorial Part III – How Things are Computed,

The Ω without subscript represents the present overall density parameter: Ω=Ω_Λ+Ω_m+Ω_r, which adds up to unity in the case of flat space.​

@pbuk

 

[Jorrie]

Jim, I don't quite understand your objection against https://light-cone-calc.github.io/, because the two give identical outputs for the Planck + BAO input data, i.e.

against https://light-cone-calc.github.io/ :

Both deviate from the Planck + BAO input data for Ω_m, for reasons discussed before.
IMO, it is simply a matter of Lightcone not taking the error bars into account. To include those would be an unnecessary complication for a relatively simple educational tool. I will update the UI and the Tutorial to explain the rationale and then remove the "Trial version" in the title.

Besides that, the newer version has the additional functionality of a full precision CSV output option.

If you want to preserve the previous version visibly on the Forum, simply put that link in your Forum signature, but mark it as "alternative UI" or something to that effect.

 

[Jorrie]

Ok, I have made the changes discussed above in the UI. Must still update Tutorial to explain.
An important change to take note of, is that I have reduced the mapping value of $\Omega_{\Lambda,0}$ input by 0.0001 in order to accommodate radiation density into flat space and remove any ambiguity in the UI or output data. So for now there is nothing extra to be done in the expansion calculation module.

The Planck collaboration says above Table 2: "The top group of six rows are the base parameters, which are sampled in the MCMC analysis with flat priors. The middle group lists derived parameters." $\Omega_{\Lambda,0}$ does not appear in the top group, but baryons and dark matter do. Hence I took it that $\Omega_{m,0}$ takes priority and so I changed $\Omega_{\Lambda,0}$ by the mentioned small amount.

@pbuk and @JimJCW. Comments?

 

[JimJCW]

Jim, I don't quite understand your objection against https://light-cone-calc.github.io/, because the two give identical outputs for the Planck + BAO input data, . . .

Both deviate from the Planck + BAO input data for Ω_m, for reasons discussed before.

Among Ω₀, Ω_Λ,0, Ω_m,0, Ω_R,0 and z_eq, only three of them can be used as inputs because of the following two relations:

LightCone8 (https://burtjordaan.github.io/light-cone-calc.github.io/) correctly uses only three: Ω₀, Ω_Λ,0, and z_eq, but LightCone8.1.2 - Jorrie Trial UI (https://light-cone-calc.github.io/) incorrectly uses four: Ω₀, Ω_Λ,0, Ω_m,0, and z_eq. This causes the discrepancy in LightCone8.1.2 (see Post #30, #40, and #42).

I noticed that in LightCone8.1.2 the inputted Ω_m,0 is used only in calculating Ω_R,0 printed to the right. The rest of the calculations is the same as LightCone8, using only Ω₀, Ω_Λ,0, and z_eq. Let me illustrate this using an exaggerated example (setting Ω_m,0 = 0.9):

The output remains the same as in LightCone8:

So, using both Ω_Λ,0 and Ω_m,0 as inputs at the same time is incorrect and produces discrepancies.

Suggestion:

We can use Ω_m,0 and Ω_R,0 as derived quantities and print them on the right-hand side:

 

[Jorrie]

Suggestion:

We can use Ω_m,0 and Ω_R,0 as derived quantities and print them on the right-hand side:

View attachment 305466

Oops, yes thanks for the headsup - I see now that the table calculation module ignores the matter density input value. I will temporarily reset the old input tables. But I would still like to use Ω_m,0 as one of the primary inputs (for reasons that I mentioned in my prior post). So it would mean swapping Ω_L and Ω_m in what you have above.

To do the change in primary input, @pbuk must also alter his calculation module to use Ω_m,0 as primary input. I will coordinate with him to get us there.

 

[JimJCW]

Oops, yes thanks for the headsup - I see now that the table calculation module ignores the matter density input value. I will temporarily reset the old input tables. But I would still like to use Ω_m,0 as one of the primary inputs (for reasons that I mentioned in my prior post). So it would mean swapping Ω_L and Ω_m in what you have above.

To do the change in primary input, @pbuk must also alter his calculation module to use Ω_m,0 as primary input. I will coordinate with him to get us there.

Please see Post #13:

If Ω_m,0 is used as input (see Post #2, where s_eq = z_eq + 1),

Ω_Λ,0 = Ω₀ - Ω_m,0 (z_eq + 2) / (z_eq + 1)
Ω_R,0 = Ω_m,0 / (z_eq + 1)

@pbuk

 

[Jorrie]

Yes, that's correct.

 

[pbuk]

To do the change in primary input, @pbuk must also alter his calculation module to use Ω_m,0 as primary input. I will coordinate with him to get us there.

The underlying model (since 24 July) does use Ω_m,0, but only if Ω_Λ,0 is not provided by the UI coupling. In that case it will apply the whole of the Ω_rad,0 adjustment to Ω_Λ,0, which I think we have agreed is not the best thing to do. If Ω_Λ,0 is provided it will apply the whole of the Ω_rad,0 adjustment to Ω_m,0.

    // Use omegaLambda0 if it is provided.
    if (props.omegaLambda0 != null) {
      omegaLambda0 = props.omegaLambda0;
      omegaM0 = (omega0 - omegaLambda0) * (sEq / (sEq + 1));
    } else if (props.omegaM0 != null) {
      omegaM0 = props.omegaM0;
      omegaLambda0 = omega0 - omegaM0 * ((sEq + 1) / sEq);
    } else {
      throw new Error('Must provide either omegaM0 or omegaLambda0');
    }

(see https://github.com/cosmic-expansion...0b12217c50ce8991181686fd406/src/model.ts#L156)

I think what we are now suggesting is that if both Ω_m,0 and Ω_Λ,0 are provided we should apply the Ω_rad,0 adjustment proportionately across Ω_m,0 and Ω_Λ,0?

I'll have a look at this.

 

[Jorrie]

I think what we are now suggesting is that if both Ωm,0 and ΩΛ,0 are provided we should apply the Ωrad,0 adjustment proportionately across Ωm,0 and ΩΛ,0?

I'll have a look at this.

Yes, although I started to think we must use Ω_m,0 (as the more directly established parameter), I guess that since we do not yet understand why the Planck collaboration have elected to present the data with this apparent inconsistency, it may be best to take their exact values at face value as inputs.

Since we are desirous to keep Ω₀ = 1, I suppose we can decide how to process that. Adjusting proportionately across both seems to be the more neutral scheme.

 

[JimJCW]

Yes, although I started to think we must use Ω_m,0 (as the more directly established parameter), I guess that since we do not yet understand why the Planck collaboration have elected to present the data with this apparent inconsistency, it may be best to take their exact values at face value as inputs.

Since we are desirous to keep Ω₀ = 1, I suppose we can decide how to process that. Adjusting proportionately across both seems to be the more neutral scheme.

The source of our problem is that Planck 2018 results. I data is incorrect for a flat universe:

We shouldn’t use these numbers as given at the same time.

We have been using Ω_Λ,0 as input and Ω_m,0 and Ω_R,0 as derivatives. We are planning to use Ω_m,0 as input and Ω_Λ,0 and Ω_R,0 as derivatives. I think either one is good.

@pbuk

 

[Jorrie]

The source of our problem is that Planck 2018 results. I data is incorrect for a flat universe:
View attachment 305565
We shouldn’t use these numbers as given at the same time.

Yea, you are right. Trying to use all 4 will give inconsistencies.
For now, let's leave it as it is.

 

[Jorrie]

If we ever find Omega_0 slightly above 1, the most likely culprit will be dark matter. Here is a graph for Omega_0 = 1.1 (an exaggerated case for visibility)

Interesting how Omega will first rise (in this case overshooting the the "current 1.1" slightly) and then being dragged down to unity again by dark energy dominance.

 

[JimJCW]

If we ever find Omega_0 slightly above 1, the most likely culprit will be dark matter. Here is a graph for Omega_0 = 1.1 (an exaggerated case for visibility)
View attachment 305573
Interesting how Omega will first rise (in this case overshooting the the "current 1.1" slightly) and then being dragged down to unity again by dark energy dominance.

The expansion of space in the Big Bang model makes many situations very complicated. I often use the LightCone calculator to help me to get pictures in my mind. The following two pictures are similar to yours:

For Ω₀ = 1:

For Ω₀ = 0.9: