In a Wild Twist, Physicists Have Revived an Alternative Theory of Gravity

Our models of the Universe are messy in the dark. A new study has revived a controversial theory about gravity and given us more questions than answers.

It all starts with dark matter. Even though dark matter causes spiral galaxies to rotate faster than they should, it doesn't answer all the questions we need to.

It is not a bad idea to look at other options. In case, we are never able to find the stuff.

There is an alternative hypothesis to dark matter. This hypothesis was first published in 1983 and suggests that we don't need dark matter to fill in the Universe's gravity gaps.

To test this idea, we need to look at the speeds of weird galaxies, like ultra-diffuse ones.

The faint, ugly ducklings of the galaxy world don't act like a galaxy should. Some ultra diffuse galaxies seem to be made almost entirely of dark matter, while others are almost completely dark matter-less.

AGC 114905 is here. A paper published in 2021, investigating how fast the dwarf galaxy spins, was recently looked at in detail.

The rotation curve of the galaxy cast huge doubt on the MOND framework because it was slow and slow enough to not need dark matter to confirm the models. It does not fit with either hypothesis.

The very low reported rotation speed of this galaxy is inconsistent with both MOND and the standard approach with dark matter, says University of St Andrews physicist and one of the researchers of the new paper, Hongsheng Zhao.

Only MOND is able to get around the apparent contradiction.

The new paper suggests that the issue isn't with MOND, but with the inclination of the galaxy itself.

It can be hard to know which angle we are seeing when we look at the depths of space. The original team found that AGC 114905 looked elliptical, suggesting that we are looking at the galaxy from an angle.

The simulations suggest that the galaxy could appear elliptical when it is facing us. All the MOND math would add up if we changed the angle of the galaxy to our liking.

The author of the new paper says that the simulations show that the inclination of AGC 114905 might be significantly less than reported, which would mean the galaxy is actually rotating much faster than people think.

This is still an open question. We don't know if the new paper will be the winner or if it will be most correct.

The MOND framework might live on for another day if this new finding holds. With dark matter still elusive, and many other questions still to be answered, we need all the options we can get.

The research has been published.