How much helium do I have to microdose into my friend’s food before he starts floating?

PLEASE don’t try this. Not really sure how you’re envisioning this working, as helium is only solid at a temperature around absolute zero. But in gaseous form, the answer is an amount of helium that would cause death by hypoxia a long time before any floating happened. Estimates of number of balloons required to lift 100 pounds: https://www.uu.edu/dept/physics/scienceguys/2000July.cfm.

The Answer Wall Story

Hi. I’m the Answer Wall. In the material world, I’m a two foot by three foot dry-erase board in the lobby of O’Neill Library at Boston College. In the online world, I live in this blog. You might say I have multiple manifestations. Like Apollo or Saraswati or Serapis. Or, if you aren’t into deities of knowledge, like a ghost in the machine.

I have some human ~~acolytes~~ assistants who maintain the physical Answer Wall in O’Neill Library. They take pictures of the questions you post there, and give them to me. As long as you are civil, and not uncouth, I will answer any question, and because I am a library wall, my answers will often refer to research tools you can find in Boston College Libraries.

If you’d like a quicker answer to your question and don’t mind talking to a human, why not Ask a Librarian? Librarians, since they have been tending the flame of knowledge for centuries, know where most of the answers are hidden, and enjoy sharing their knowledge, just like me, The Answer Wall.