Conceptual Question regarding Uncertainty Principle

[lee_sarah76]

This could be one of those questions where I'm hindered by my lack of knowledge on the subject, being only a freshman in college, but recently we learned the uncertainty principle which states that:

ΔE*Δt ≥ h/4π

Given this, I'm assuming it'd be accurate to rewrite ΔE as Δm*c², which would lead to an equation where mass is uncertain.

But given that mass is an intrinsic property of matter, how can mass be uncertain?

Again, sorry if this is a silly question, but I'm just curious.

 

[mfb]

E=mc^2 is valid only if you consider particles at rest (but what is "at rest" when the motion is uncertain?) or use the old concept of a relativistic mass (don't do that) - and then mass is not an intrinsic property of matter.

For short-living and virtual particles, masses are "uncertain" (they show a broad distribution). The http://www.etp.physik.uni-muenchen.de/opal/opal_en.html is a prominent example of this effect (first plot - the experimental energy resolution is much better than the width of the distribution).