AI Calibration

[Alan Grayson]

I plan to check it out again, but I'm pretty sure AI claimed the Hubble's law gives us the velocity and distance of galaxies in the present, NOW. WRT distance, it claims that using standard candles, we get the actual distance NOW, not the distance when the light left some galaxy 10 billion years ago. Is there concurrence among the humans here? TY, AG

[Alan Grayson]

I just checked with AI again. Gemini says the following: 

"The Luminosity Distance ($D_L$) is a measure that accounts for the expansion, but precisely because it includes the energy loss and time dilation effects of the expansion, it gives a distance value that is larger than the current, real physical distance (Proper Distance, $D_P$) [1.2].

The standard candle provides $D_L$, but you need to know the redshift ($z$) and use the cosmological model to truly calculate the Proper Distance ($D_P$).

[Alan Grayson]

On Sunday, December 14, 2025 at 9:20:55 PM UTC-7 Alan Grayson wrote:

I just checked with AI again. Gemini says the following: 

"The Luminosity Distance ($D_L$) is a measure that accounts for the expansion, but precisely because it includes the energy loss and time dilation effects of the expansion, it gives a distance value that is larger than the current, real physical distance (Proper Distance, $D_P$) [1.2].

The standard candle provides $D_L$, but you need to know the redshift ($z$) and use the cosmological model to truly calculate the Proper Distance ($D_P$).

Gemini also posted as follows:

 The relationship between the Proper Distance ($D_P$), Luminosity Distance ($D_L$), and the redshift ($z$) is defined by the Etherington's distance-duality equation:

$$D_L = D_P (1 + z)$$

• For nearby objects, $z \approx 0$, so $D_L \approx D_P$.

• For very distant objects with significant redshift (e.g., $z=1$), $D_L = 2 \times D_P$. The Luminosity Distance is twice the "actual distance now" because of the compounding dimming effects.

I might have reached the wrong conclusion because of what another AI claimed, namely Co-pilot. I will check out its comments to see if they're consistent with Gemini. AG

[Brent Meeker]

You should check with Ned Wright's Tutorial page: 

https://www.astro.ucla.edu/~wright/cosmo_02.htm    

which shows how the various distance measures differ depending on the cosmological model.  He also links to a Javascript calculator
 
https://www.astro.ucla.edu/~wright/CosmoCalc.html

Brent

--
You received this message because you are subscribed to the Google Groups "Everything List" group.
To unsubscribe from this group and stop receiving emails from it, send an email to everything-li...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/everything-list/ead11ee9-df7d-4e35-aeed-518d0070e598n%40googlegroups.com.

[Alan Grayson]

On Sunday, December 14, 2025 at 9:40:23 PM UTC-7 Alan Grayson wrote:

On Sunday, December 14, 2025 at 9:20:55 PM UTC-7 Alan Grayson wrote:

I just checked with AI again. Gemini says the following: 

"The Luminosity Distance ($D_L$) is a measure that accounts for the expansion, but precisely because it includes the energy loss and time dilation effects of the expansion, it gives a distance value that is larger than the current, real physical distance (Proper Distance, $D_P$) [1.2].

The standard candle provides $D_L$, but you need to know the redshift ($z$) and use the cosmological model to truly calculate the Proper Distance ($D_P$).

Gemini also posted as follows:

 The relationship between the Proper Distance ($D_P$), Luminosity Distance ($D_L$), and the redshift ($z$) is defined by the Etherington's distance-duality equation:

$$D_L = D_P (1 + z)$$

• For nearby objects, $z \approx 0$, so $D_L \approx D_P$.

• For very distant objects with significant redshift (e.g., $z=1$), $D_L = 2 \times D_P$. The Luminosity Distance is twice the "actual distance now" because of the compounding dimming effects.

I might have reached the wrong conclusion because of what another AI claimed, namely Co-pilot. I will check out its comments to see if they're consistent with Gemini. AG

Here's Co-pilot's reply, obviously inferior to Gemini; 

Bottom line: standard candles provide actual distance estimates grounded in physics, but those estimates are not exact single numbers — they are measurements with known uncertainties that astronomers reduce by calibration, corrections, and multiple independent methods.