The best definition I've heard, which I ascribe to Vic Stenger, is that it is what is conserved when a physical system is translated in the time dimension. This comes from the Noether theorem.
Of course, relativity changes this a bit, since there is no longer a unique time dimension. In relativity, what is conserved is a 4-vector when the system is translated in spacetime. Conventionally we call that vector the "mass-energy-momentum" vector. The magnitude of that vector is just the rest mass of the system, and that is an intrinsic property of the system. E=mc^2 is just a famous equation referring to the fact that components of a vector change when you change the coordinate system (which depends on the observer) - much like the width and height of a 2D object change into each other as you rotate the x-y axes of the coordinate system. Cheers On Sun, Feb 14, 2016 at 09:34:09AM -0500, spudboy100 via Everything List wrote: > You know, I have never heard a decent definition of what energy is? I learnt > in grade school was that energy was the ability to do work. Yah! Now that > sounds really, scientific, not. I refined the definition, to be "matter in > motion." Anyone have a better definition? "It takes energy.." > > > > -----Original Message----- > From: Terren Suydam <[email protected]> > To: everything-list <[email protected]> > Sent: Sat, Feb 13, 2016 9:47 pm > Subject: Re: Gravitational Waves Detected By LIGO! > > > > Great, but what is the specific way in which mass is converted into the > energy required to produce gravitational waves? When planetary orbits decay, > kinetic energy is lost... No mass is converted. > On Feb 13, 2016 1:20 PM, "John Clark" <[email protected]> wrote: > > > On Sat, Feb 13, 2016 at 1:00 AM, Terren Suydam <[email protected]> > wrote: > > > > > > > > Sure, but John said the black holes lost 3 solar masses, which was converted > into gravitational waves... how? Fusion and fission are easy examples of > mass to energy conversion - so what's the specific interaction here according > to theory? > > > > > Einstein found in General Relativity a new law of nature, he said it takes > energy to make gravitational waves and that an accelerating mass produces > gravitational waves, just as Maxwell said a accelerating charged particle > makes a electromagnetic wave. Normally this effect is far too small to be > important and can be ignored, but when it's something as massive as a black > hole and its vibrating at almost the speed of light as it tries to become > spherical we now know that gravity waves can not be ignored and Einstein was > right. General Relativity has passed its most stringent test yet and passed > it with flying colors! > > John K Clark > > > > > > > > > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. -- ---------------------------------------------------------------------------- Dr Russell Standish Phone 0425 253119 (mobile) Principal, High Performance Coders Visiting Senior Research Fellow [email protected] Economics, Kingston University http://www.hpcoders.com.au ---------------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
