# Change law of gravitation to remove dark energy and dark matter

The speed of star on the outer of are solar system is not according to the visible mass.
Change the law of gravitation F = 1/r^2 to fix this.
Galaxies far away are moving away with increasing speed.
Change the law of gravitation F = 1/r^2 to fix this, include a repulsive force to fix.
Would this fix violate other measurements , which ones ?

fresh_42
Mentor
Would this fix violate other measurements , which ones ?
Yes. If I understood it correctly, then dark energy can be measured by red and blue shifts of photons leaving / falling into the gravitational potentials in the CMB. That gravitation works as we think it does is proven by the visible matter and energy. The computer models with dark matter match the real world. However, I am not certain that this is a reliable description, my source was pop science.

Ibix
There are plenty of alternate gravity theories. I don't think any of them are completely satisfactory - they can explain some things but not others.

PeroK
Homework Helper
Gold Member
The speed of star on the outer of are solar system is not according to the visible mass.
Change the law of gravitation F = 1/r^2 to fix this.
Galaxies far away are moving away with increasing speed.
Change the law of gravitation F = 1/r^2 to fix this, include a repulsive force to fix.
Would this fix violate other measurements , which ones ?
See, for example:

https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics

Ibix
Ibix
Yes. If I understood it correctly, then dark energy can be measured by red and blue shifts of photons leaving / falling into the gravitational potentials in the CMB.
I think you are thinking of the integrated Sachs-Wolfe effect, which is a result of dark energy modifying the gravitational potential wells of galaxy clusters, causing a change in the redshift of CMB photons as they pass through. This is not the same as the Sachs-Wolfe effect, which is derived from properties of the CMB alone.

PeterDonis
Mentor
2019 Award
The speed of star on the outer of are solar system is not according to the visible mass.
What are you referring to here? Do you mean galaxy rotation curves? Our solar system is not a galaxy.

PeterDonis
Mentor
2019 Award
Change the law of gravitation F = 1/r^2 to fix this.
What proposed model are you referring to? Can you give a reference?

BWV
Didn’t they find some galaxies with no dark matter that behaved just like existing theory would predict?

DaveC426913
Gold Member
Didn’t they find some galaxies with no dark matter that behaved just like existing theory would predict?
Yeah - but...
How do they detect whether galaxies have dark matter or not, except by how the stars behave?

BWV
Yeah - but...
How do they detect whether galaxies have dark matter or not, except by how the stars behave?
right, but observations of several galaxies behaving as theory would predict without needing dark matter supports the existence of dark matter and puts the kibosh on (some,most,all?) alt gravity hypothesis

DaveC426913
Ibix
Didn’t they find some galaxies with no dark matter that behaved just like existing theory would predict?
From previous discussion on here I gather that some modified gravity theories can handle that. Something to do with long-range effects from nearby galaxies, or something - I don't know the details.

Change the law of gravitation F = 1/r^2 to fix this.
How do you want to change the laws? If there are any physics laws, and they are laws, they aren't changable. I have also read that the others that these laws are hipotetical and have something wrong. If we are speaking about something not fixed, we are speaking about teories, not laws. I think that here there is a misundrstanding

Ibix
I think that here there is a misundrstanding
Both "laws" and "theories" are words for things we've invented. We don't generally regard either as being changed, but we certainly develop newer theories (nothing new tends to get called a law these days) which supersede them.

vincenzosassone, berkeman and fresh_42
PeterDonis
Mentor
2019 Award
There are plenty of alternate gravity theories.
And the OP has not said which one he is asking about, which means we have no valid basis for discussion.