cfgauss

Momentum does too, but we say that mass-energy does, because, well, that's what's happening!

Yes, E=mc^2 is only valid at rest, but E=gamma mc^2 works for not-at-rest stuff, and it doesn't imply it either! They both simply imply that they are related.

Also, elements are particles! Mostly Hydrogen and Helium (also, small amounts of some stuff heavier) were created in the Big Bang. It formed stars, which fused it into the good stuff, exploded, and made more good stuff.

Shadowy Man

What do you mean by "mass-energy"?

Well, yes.. elements are particles... but they are groups of particles. The particles themselves were not created in stars. Stars are just reorganizing the particles into different elements.

Lithium was also created in the Big Bang but it is destroyed in stars (deuterium too). So next time you take your lithium think about how you are connecting with the primordial universe!

cfgauss

Mass-energy is the E in E=mc^2. You increase speed, you increase mass-energy, but not mass.

Physicists refer to "elements" as particles all the time ("elements" sounds so much less scientific, doesn't it?). And yes, everything below Iron was created in the Big Bang, but mostly Hydrogen and Helium. Though the Lithium we take could also have been created by a star .

Jesse

Catching up on old posts (this is from p. 1):

HawkingFan:
The laws of science do not distinguish between the past and the future. Entropy is only one example of the "arrow of time"--a thing that is able to distinguish the past from the future, giving a direction of time. There are 3 arrows of time:
1--thermodynamic: entropy increases
2--psychological: direction which we feel time pass, remember the past but not the future.
3--cosmological: direction of time in which the universe is exanding and not contracting.

cfgauss:
Your arrow of time thing doesn't even make sense.

Cosmologists talk about the origin of the "arrow of time" problem on a regular basis. The basic problem is that all our fundamental laws of physics are time-symmetric, but a number of phenomena in nature appear to be irreversible--entropy tends to increase rather than decrease, "retarded" solutions to the equations of electromagnetism are observed while "advanced" ones are not, etc. See this page, for example:

http://cdfinfo.in2p3.fr/~bouquet/Bricmont/node3.html

here's another good one:

http://plato.stanford.edu/entries/time-thermo/

Two good books on this subject are Huw Price's Time's Arrow & Archimedes' Point and Roger Penrose's The Emperor's New Mind.

Friar Bellows

Well, it would depend on what you meant by mass, as there are several different physical conceptions of it, e.g. inertial, rest, relativistic, transverse, longitudinal. If by mass-energy you mean the E in:

E^2 = p^2 * c^2 + m^2 *c^4

(where m is the rest mass, and p is the 3-momentum) then you're right.

No, this is a faulty analogy. In d = rt you have two variables on the right hand side. In F = kx you also have two variables (if you're dealing with springs, k will depend on the spring's elasticity) on the right hand side. On the other hand, in E=mc^2 you have only one variable on the right hand side, and one constant (i.e. the speed of light).

That there is no "universal frame of reference" is a vital part of special relativity. But the cosmological model (that goes beyond SR) which (so far) does a good job of describing our universe allows a universal frame of reference, due to reasons of symmetry. This universal frame of reference is the one in which the universe appears isotropic, at least on a large scale. It is also known as the "Hubble Flow". Similarly, there is a universal time, which can (for example) be synchronised to the mean density (or temperature) of the universe.

Shadowy Man

I think Friar Bellows clarified your first point here.

Astrophysicists refer to elements as elements all the time. And no, elements does not sound much less scientific. And no, everything below Iron was not created in the Big Bang. The only elements of consequence created in the Big Bang were Hydrogen, Helium, Deuterium, and Lithium.

"Heavier" elements were created in stars.

Hawkingfan

Hawking clearly says that it does. I'll take his word over yours, thanks. And the mass of a black hole increases all the time.
You misunderstood me. The particles that are left over are the ones that did not have an antiparticle to annihilate with. Do you want references for that statement, or would you even care? You have a tendency to ridiculously discredit any references we mention.

Wyz_sub10

I, too, thought that mass increased with velocity.

BTW, here is an "interesting" and "logical" piece dealing with this (no shortage of this stuff on the www, to be sure).

Reletavistic Mass Increase

Shadowy Man

That was clearly written by someone who hasn't spent a lot of time studying, and certainly not researching, special relativity.

The rest mass of a particle is an invariant in SR. At this point it is best to start thinking of momentum and energy in terms of four-vectors. A very well written, understandable by a layperson book to look at would be Spacetime Physics by Edwin F. Taylor and John Archibald Wheeler.

cfgauss

Jesse:
I'm saying Hawkingfan's "arrow of time" thing makes no sence, I know what the arrow of time *is*. But to say or to any way imply that the arrow of time has anything to do with preception is nonsense.

Friar Bellows:
The way mass is currently defined is as "invariant mass," that's the mass of an object at rest. Anything else isn't mass.

My analogy was perfectly fine. It simply says that mass and energy are related, just like force and distance in a spring, or distance and time at a speed. You can easily only consider k and v to be constant in these cases. Also, c may well be a varyable, too!

I can pick the frame of the Apollo 11 astronaughts urine after it was ejected from the spaecraft, if I want, but there's nothing special about it. Often we pick coordinate frames wherein things look "nice" (why do you think we use rectangular coordinates so often?), but there's nothing special about any of them. You get the same results in all of them, but it's easier to use one or two. There is, however, no *prefered* frame! Just nice ones and not as nice ones.

Shadowy Man:
Everything below Iron *was* created (possibly things above, but we can't be sure) in the Big Bang, just in *very* small amounts. (Technically, they were *all* created *shortly after* the Big Bang.) But, believe it or not, when you've got the ammount of matter in the universe crammed into a teeny space, just cool enough to not blow itself apart, there will be some fusion taking place . Most of the stuff above Helium, however, was created in stars.

Hawkingfan:
Do you understand what the "popular" in popular science means? It means "dumbed down so you can understand it without complexities and details."
E=mc^2 is only valid for an object at rest. If you talk about adding energy then it's not at rest, and you're talking about things in different frames. That kind of logic gets you confused as how you could get to Alpha Centauri, 4 ly away, in a weekend going near the speed of light.

The statment "space is made up of particles left over from particle/antiparticle annihilations" clearly implies that they are a product of it. If I were being nitpicky, like you claim, I would've pointed out that it doesn't make any sense to say that *space* it made of it.

Wyz_sub10:
The author makes a common mistake in the article. How did the Hydrogen get to near the speed of light? It accelerated. Acceleration is *not* relative, so there *is* a difference between the two, and we can tell wich of the atoms is in motion. Though the energy required to accelerate something that fast (assuming that the "mass" increase he gave is correct) in in the ballpark of 9x10^34 J.

Check this out for a good explination of relativistic and invariant mass.
http://www.desy.de/pub/www/projects/...y/SR/mass.html