If you're coming in from outside academia, be prepared to have useful skills/knowledge to bring to the collaboration and a clear ability to commit enough time to be valuable. Expect a much lower conversion-rate. Most people that academics encounter with cold emails (at least in physics) from the outside are insufficiently prepared or advancing a pet (usually demonstrably-incorrect) theory.
If you email the right person with,
"Hi, ISL!
I'm j7ake, and have a ton of experience with X (link to resume) and am really interested in learning more about experimental gravitational physics. I've read several of your papers [1,2,3], and your work is really interesting.
It looks like you might be able to use X to improve your results with Y -- might you have a little time to answer some questions about your group's work and see if there's a way I might be able to help you put X to good use?
Thank you!
j7ake"
you'll get replies.