system
Given the following post, respond as if you're commenting on Reddit:
human
What are some experimental observations that have been made that do not currently agree with our current understanding of physics?

I'm interested in seeing what kind of interesting things can't fully be explained. To clarify I'm taking about things that can't be explained by widely accepted theories. 
BONUS QUESTION:
What are the theories that have been developed to explain these events.
gpt
Based on astronomical and cosmological observations, there is a lot more mass in the universe than we can see. We do not know what comprises this mass. 

The cosmic microwave background is the same temperature in every direction, even though regions at opposite sides have never been in causal contact with each other.

If bubbles collapse fast enough they release a flash of light.

To name a few.