 |
 | Home | Contact Us | FAQ | Search & Site Map | Link to Us |
 | Sign In | Join | Other 45 Sites in Network |
Natural Science Forum / Physics / General Physics / November 2008Gravity and mass-energy equivalence
Hi. According to Einstein's theories of relativity, mass and energy are equivalent. So when you add energy, you also add mass, and vice versa. This would imply that a spring compressed is slightly heavier than one not compressed, for example (although too small to measure). I'd also assume this would apply to gravity. As two objects approach under gravity, their potential energy decreases -- but would not that also correspond to a decrease in mass? For example, isn't the Earth slightly lighter than it would be if it was a strew of asteroids? So as objects fall together under gravity, mass is converted to energy, right? Therefore as a planet accretes, it heats up due to some of the mass being turned into energy. Now, what about with a Black Hole? Suppose we drop something into a Black Hole. It loses gravitational potential energy as it falls down the hole. But given the hole is (at least according to relativity -- whether or not a "true singularity" _really_ exists is likely something that will only be known once we have a quantum theory of gravity), an infinitely deep gravity well, should not a point be reached where _all_ the mass turns to energy? If so, then what happens to the object? Does it just poof, quit existing? Become a weird massless blob? If that's so, then wouldn't the grav. force then drop to zero? Does this mean the inside of a BH is nothing but pure energy? > Hi. > [quoted text clipped - 21 lines] > massless blob? If that's so, then wouldn't the grav. force then drop > to zero? Does this mean the inside of a BH is nothing but pure energy? The mass-energy of what falls into the black hole is added to the mass-energy of the black hole. What happens on the inside of the event horizon is not observable to someone on the outside. One expects the tidal forces increase without limit as "whatever" falls toward a singularity into the future. > > Hi. > [quoted text clipped - 28 lines] > One expects the tidal forces increase without limit as "whatever" > falls toward a singularity into the future. Alice in Wonderland >>> Hi. >>> According to Einstein's theories of relativity, mass and energy are [quoted text clipped - 26 lines] > > Alice in Wonderland Except once you go down the rabbit hole of a black hole, you ain't coming back. Welcome to the reality of the universe, John. It was never the way you wanted it to be. Sam My equation says it all TreBert > Hi. > According to Einstein's theories of relativity, mass and energy are > equivalent. So when you add energy, you also add mass, and vice versa. > This would imply that a spring compressed is slightly heavier than one > not compressed, for example (although too small to measure). Right. While that particular case is too small to measure (yet), we can actually measure that, for example, the kinetic energy of the electrons in an atom contributes to the mass. > I'd also assume this would apply to gravity. As two objects approach > under gravity, their potential energy decreases -- but would not that > also correspond to a decrease in mass? For example, isn't the Earth > slightly lighter than it would be if it was a strew of asteroids? Right. This is also measurable, by comparing the orbits of the Earth and the Moon. As a proportion of total mass, the gravitational binding energy of the Earth is slightly different from that of the Moon. If the gravitational mass didn't decrease as you describe, the Earth and Moon would fall toward the Sun with slightly different accelerations (the "Nordtvedt effect"), which would be observable with Lunar laser ranging. You might want to get a copy of Cliff Will's nontechnical paperback book _Was Einstein Right?_, which has a nice chapter on this. > So > as objects fall together under gravity, mass is converted to energy, > right? Therefore as a planet accretes, it heats up due to some of the > mass being turned into energy. This is something a bit different. As objects fall together, total energy remains constant -- (positive) kinetic energy increases, while (negative) potential energy becomes more negative. If you're looking at the mass, or energy, of a system of two objects falling towards each other, it will remain very nearly constant ("very nearly" because a tiny bit of energy will be radiated away in electromagnetic and gravitational energy). When the two objects collide, the kinetic energy will be converted into other forms of energy, mostly heat. As this energy is radiated off into space, the remaining mass and energy will decrease, and you will end up with slightly less mass. But it's not as simple as "mass converted to energy." > Now, what about with a Black Hole? Suppose we drop something into a > Black Hole. It loses gravitational potential energy as it falls down [quoted text clipped - 3 lines] > gravity), an infinitely deep gravity well, should not a point be > reached where _all_ the mass turns to energy? As an object falls toward a black hole, some of its mass is converted to energy. The maximum efficiency is about 29% -- pretty high, but not 100%. Note that the picture of a black hoke as an "infinitely deep gravitational well" is misleading -- what's relevant is only the gravitational field outside the horizon, since nothing inside the horizon can get out. Steve Carlip On Nov 21, 6:30 pm, carlip-nos...@physics.ucdavis.edu wrote: > > Hi. > > According to Einstein's theories of relativity, mass and energy are [quoted text clipped - 53 lines] > > Steve Carlip Thanks for the explanation. > Hi. > > According to Einstein's theories of relativity, mass and energy are > equivalent. So when you add energy, you also add mass, and vice versa. > This would imply that a spring compressed is slightly heavier than one > not compressed, for example (although too small to measure). Education is hopeless. > I'd also assume this would apply to gravity. As two objects approach > under gravity, their potential energy decreases -- but would not that > also correspond to a decrease in mass? Kinetic energy. If you want a decrease in mass you need gravitational binding energy. Yer friendly neighborhood neutron star is missing about 15% of its unbound total baryon mass. Potential energy is a particularly slippery concept re potential vs. what? > For example, isn't the Earth > slightly lighter than it would be if it was a strew of asteroids? So [quoted text clipped - 12 lines] > massless blob? If that's so, then wouldn't the grav. force then drop > to zero? Does this mean the inside of a BH is nothing but pure energy? Gravitation is an efficient engine to convert rest mass to energy - better than 30% during event horizon infall. Now tell us how long it takes an external bowling ball to pass through the event horizon - and how much energy ends up kinetic rather than radiated. Put the bowing ball at the end of a carbon nanotube cable and lower it in. If it passes through the event horizon, can you pull it back out? Feel free to use a galactic core black hole so event horizon local curvature asymototes toward zero.  SignatureUncle Al http://www.mazepath.com/uncleal/ (Toxic URL! Unsafe for children and most mammals) http://www.mazepath.com/uncleal/lajos.htm#a2 > > Hi. > [quoted text clipped - 46 lines] > Uncle Alhttp://www.mazepath.com/uncleal/ > (Toxic URL! Unsafe for children and most mammals)http://www.mazepath.com/uncleal/lajos.htm#a2 -------------------- idiot farter gravitation has nothing to do with parrots nor with 'curvature of space' 2 while you talk about 'potential energy of gravity' you have to take in account ALL ! the involved components in it and that is surely far beyond you poor parroting ability!! Y.P -------------------------------- -------------------------- > > > Hi. > [quoted text clipped - 66 lines] > > - Show quoted text - Round geometry space motion decelerates outward motion of mass then accelerates mass toward its center. if mass resists space motion creates weight. Space motion affects time then time affects light. Mitch Raemsch |
Reply to this Message |
 Sign In
 Join
 My Latest Posts My Monitored Threads My Blog My Photo Gallery My Profile My Homepage Start New Thread Enable EMail Alerts Rate this Thread
|
©2009 Advenet LLC Privacy Policy - Terms of Use
This website includes both content owned or controlled by Advenet as well as content owned or controlled by third parties.