People. You need your physics. You really, really need it. If you go into a different universe with different physics, starving to death will probably not be a problem. Okay, look: if there are different energy levels in atoms, such that lasers come out at different wavelengths, there is a reason for that. Atoms do not pick electron shells out of a hat. It comes from very, very basic physics. So if that very, very basic physics is different -- different mass of electron? different charge? -- a person who is transplanted into that new physics will interact with it immediately. Your neurons firing? Physics. Your skin remaining intact in the shape it's currently in? Physics.
You do not! Aaaaaagh, sorry, this is just too much. You do not keep a set of electrons labeled, "$yourname's electrons," and they all go around and around like wee planets at the Bohr radius. That is not what electrons do! We know this! We have known this for quite some time! Longer than my grandparents have been alive, we've known this! You don't even keep a set of protons that's all yours. It's not just those wacky mobile electrons. It's everything, everything, everything.
Never mind breakfast. Never mind breathing. In a split second between breaths, sitting on your chair, your ass and your chair have already traded approximately one gajillion* pieces of physical information. If you were suddenly in a situation where one electron you traded off from brushing the keyboard with your thumb was of a different charge or a different mass, you probably wouldn't notice, but that is not the same as being completely immersed in a different physics. Where you would, and I don't feel I am being too restrictive here, DIE. Because we are extremely physical organisms, because every biological process has physical roots, and changing the atmosphere around you is completely different from changing how atmospheric gases -- how molecular interactions in general -- work.
This is what we know as really really stupid. Insultingly stupid. Gah.
*I r teknikl Mris. This r teknikl thread.