Our knowledge about galaxy evolution comes from transforming observed galaxy properties at different redshifts to co-moving physical scales .
This transformation depends on using a cosmological model .
Here the effects of unintentional mixing of two different cosmological models on the size evolution of galaxies is studied .
As a gedanken experiment , a galaxy of fixed proper size and luminosity is moved across different redshifts .
The apparent size of this galaxy is then interpreted with a cosmological model presumed by the observer , which is different compared to the cosmology exhibited by the Universe .
In such a case , a spurious size evolution of the galaxy is observed .
A galaxy behaving according to the R _ { \text { h } } = ct and Neumann ’ s cosmology , when interpreted with the \Lambda CDM cosmological model , shows an increase in size by a factor of 1.1 and 1.3 from z = 7.5 to z \approx 0 , respectively .
The apparent size of a galaxy in a static Euclidean cosmology , when interpreted in the \Lambda CDM model , shows a factor of 23.8 increase in size between z = 7.5 to z \approx 0 .
This is in close agreement with the observational data with a size increase of a factor of 6.8 between z = 3.2 to z \approx 0 .
Furthermore , using the apparent size data , it is shown that the difference between the derived proper sizes in R _ { \text { h } } = ct , Neumann ’ s and \Lambda CDM cosmological models are minimal .