[nagant]

Dark matter theory was born by a discrepancy between distances measured to certain distant objects when measured by 1) redshift, and 2) intensity. The redshift measurement method is long-standing. The intensity method is new. The redshift method relies on a "Hubble constant" which has never been nailed down. The intensity method is considered more reliable. Redshift measurements pegged the Hubble constant at a value which relies on the universe's gravity slowing down universal expansion. Intensity measurements reveal that farther objects are, rather than slowing, accelerating away from us. It's a real conundrum which some say can be explained away with time dilation. Put another way, it can be explained away with photon decay. Both redshift and intensity methods rely on photon measurement. Since the inception of red shift measurements some scientists have argued that redshift is, at least partially, explained by the fact that time is slowing with expansion in the intervening space .....termed "time dilation". How much observed redshift is due to recession, and how much is due to time dilation, has always been the biggest question in determining the Hubble constant. However, detection of universal acceleration relies on intensity measurements, not on redshift measurements. What is it about the intensity measurement method which would inherently indicate accelerated expansion? Or are the intensity measurements accurate? Is something pushing our universe apart?

[stremba]

Your first sentence is partially right: Dark matter was born to explain a discrepancy. Unfortunately the rest is WAY off. The discrepancy had nothing to do with distance measurements. It was the fact that galaxies were observed to rotate faster than would be predicted by general relativity.

That leaves two options: either the galaxies have unobsevable matter or general relativity is not applicable to galactic rotations. Both ideas were considered seriously, but dark matter matches reality better than MOND (MOdified Newtonian Dynamics - basically the alternative to GR). MOND does better at explaining galactic rotations but does poorly when applied to larger scales than individual galaxies. DM does well at all scales. DM may be modified or abandoned as more data come in, but it’s not just a myth or a placeholder; it’s the best explanation for what we currently have observed.

[Boogieman]

That’s “dark energy” you are talking about, not “dark matter”.

“Dark matter” is the fudge factor they came up with to explain why galaxies do not rotate as expected according to the equations of relativity (the center should rotate faster than the outer arms, but we see that instead the outer arms and center complete a revolution at the same pace).