Law 1 - Energy cannot be created or destroyed
Law 2 - Entrophy increases to a maximum in a sealed system

If this is true does it mean the universe was created rather than just 'there' for infinite time as otherwise entrophy would have already increased to a maximum?

Sorry if this is a stupid question, I am just a nOOb studying GCSE physics. Thanks for any help.

___ You will not thank me for I am not actually helping... No its not a stupid question. This is the place for questions astronomy related... Your two statements are trouble to me... Both can be disputed. Just watch... and so to if they can be shown to be wrong then your second paragraph is redundant. I as you might guess I have a problem with your choice of words... 'created' is a word astronomy would shy away from. According to me. To qualify this I will addwho am I ? Just my own authority... and the quote should have been " You can not create or destroy matter." and that its been said that matter is or can be energy. I am sure much more can be said here., and will be. Welcome.... mark

The "Laws" of thermodynamics don't necessarily apply to the entire universe all at once.

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Forming opinions as we speak

Hello, Gary!

I agree with Mark: This is a very good question. You have pointed out
two very important principles that have been learned about how nature
appears to work, which seem to be incompatible with the existence of
the Universe.

The main fact here is that we do not have a theory which explains how
the Universe came into existence. We don't know where the energy
came from or why the entropy of the Universe is less than maximum.

The two principles are observed locally, but do not appear to apply to
the Universe as a whole.

One interesting possibility is that the positive energy of matter, chemical
bonds, electric fields, nuclear forces, kinetic energy and so forth is exactly
balanced by the negative gravitational potential energy of that matter.
When the Universe was created, all the particles seem to have separated
in such a way that their gravitational potential energy is exactly balanced
by the rest of their energy, so that the sum of the negative and positive
energy is always zero. That conforms to the conservation of energy law.

But that doesn't appear to answer the question about entropy, and I don't
know enough about it to add anything useful.

I hand you over now to the next higher-level expert....

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

many theorists are proposing a multiverse, or many universes, of which the big bang was just another event in the bigger multiverse.

I'd go along with that, although this article by Alan Guth explains a very good possibility that goes back pretty close to the beginning.

Well, this I think we do know the answer to: the age of the universe is finite, apparently about 13.7 billion years. Due to the particular evolution of the universe so far, there just hasn't been enough time for the entropy to go to maximum. Give it another trillion years and we'll be pretty close....

__________________
Everyone is entitled to his own opinion, but not his own facts.

That is what fits known physics. Known physics, however, breaks down under immense pressure (pun intended) found in the first trillionith, trillionith, trillionith, trillionith, of a second.

Entropy (no "h" as in enthalpy) is a big support for the BBT. Prior theories that were comfortable with infinite time for our universe (Static and Steady State theories) had a problem with this. If, however, hydrogen could pop through the cracks of the fabric of the universe or form in some other way, we would have a continual reduction in entropy that would offset the increase, but this has never been found. [Hydrogen can form nevertheless by an odd quantum process, but it is too rare to offset the rate of entropy increase found with the "arrow of time".]

This is a profound question.

The multiverse conjectures are interesting attempts to expand beyond our universe for a less special explanation for how energy could pop seemingly from nothing. It is likely that none will become a legitimate theory, which requires that it make observational predictions.

__________________
Lighten up! This is a stellar board!

I would counter that they do. However, due to the extreme distances between systems (galaxies or galactic clusters), which require millions, if not billions, of years to communicate (lightspeed) between them, and the relatively ineffectual method of communication (extremely weak EM and gravity), the effects between systems is negligible, and very strongly overridden by EM/gravity forces within those systems.

Thus, antoniseb's statement is, for all practical purposes, essentially correct.

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If I set the budget, we'd have Ares and more. Unfortunately, I don't set the budget, and Ares is just too expensive and too far out for us to accomplish our goals within the budget we were given.

If we halt the ISS, all versions of Ares, and transport Orion and Altair aboard DIRECTv3's Jupiter family of Shuttle-Derived Launch Vehicles, we just might make it back to the Moon by 2020.

Astrophysicist Sean Carroll has a book coming out in January 2010 on this and related topics. You might also scroll through this list of his postings on this and related subjects on the Cosmic Variance blog (or look at the list of links at the bottom of the first link); this one in particular is interesting.

You might ask, "why does time keep popping up in discussions of the laws of thermodynamics?". How are they related?

Conservation of energy makes an equivalent statement about a symmetry called time-translation symmetry. This means that nature doesn't care what time it is in any absolute sense, only relative time intervals are important. i.e., the laws of nature are invariant to our choice of time origin for some process. Or another way of thinking about it is that "there are no special places in time." In fact all of the conservation laws have a corresponding statement concerning an important symmetry (or an invariance) that describes the universe we live in, a concept formalized by mathematician Emmy Noether in the early 20th century. The 2nd law, usually associated with the oft-considered mysterious concept of 'entropy', is actually nothing more than a statement that concerns nature's preference in eliminating energy gradients (including pressure, concentration, etc) and the associated statistical probabilities of finding moles of particles in various places of phase space (position and momentum). It is connected with what we perceive on the macroscopic scales of our universe to be an "arrow of time".

These "laws" are not absolutes. The 1st law is in some ways broken, albeit over tiny time intervals (dt ~ h/dE), within the quantum vacuum (creation/annihilation of particle/anti-particle pairs). And as far as general relativity is concerned, the conservation of energy is apparently a "local" phenomenon; i.e., there may be no unique way (or it is at least non-trivial) to compare energies in systems separated by cosmologically significant distance/time scales (i.e., systems that live in different metrics of expanding space-time). Nevertheless, as mentioned by Jeff Root, the likelihood that the overall energy of the universe within our particle horizon is zero (or virtually so) is telling us something very important about the universe we inhabit. And the 2nd law is not a statement of absolute certainty whether some process can or cannot occur (in whatever kind of system) -- it is a statement of statistical probability regarding the behavior of lots and lots of particles.

The following is out of my league, but I seem to recall that we expect the maximum entropy of our universe to scale with the surface area of the Hubble Volume we inhabit (analogous to Hawking's black hole entropy), whereas the entropy itself scales roughly as the radius of the Hubble Volume. Thus, the difference between the two grows with time (allowing structure to arise, for example), although I (think I) can imagine this behavior might not apply in a universe dominated by dark energy, for example.

Lol wut?

Thanks for the help so far. Can someone go into more detail about this multiverse you people speak of.

Great forum by the way.

This universe is very, very, nicely tweaked. If gravity had been just a little stronger, for instance, our universe would have collapsed in upon itself and we wouldn't be here to complain about this catastrophic problem.

Thus, you might think of all the right things that took place for our universe as seeing a couple dozen dice thrown and all coming up with 6's on top, with the 6s as representing benefical things, and all the other numbers progressively less beneficial. To have this happen suggests that these dice must get thrown an awfully lot for all those 6's to come up. Thus, if there are an infinite, or near infinite, number of universes, one is bound to be just right. If so, we are in the Goldylocks' universe.

There is some claim, also, that such a view springs forth from string theory, but I am dubious about this claim, not that I remotely come close to understanding the merits of string theory, or even if it is a legitimate theory yet.

__________________
Lighten up! This is a stellar board!

That does go very close to the beginning, but as far as I can tell,
it assumes that all the energy already exists. Inflation theory was
intended to explain why the energy appears to have been so uniformly
distributed, but nothing about where it came from. In addition, my
personal view is that inflation is not needed to explain the uniformity.
Instead, I think that the uniformity came from the creation process,
whatever it was. I have no idea what it was, but I have some ideas
which may amount to a viable alternative to inflation. The essential
idea is that the creation took some time to occur, and was not an
instantaneous event. That limits the density and temperature at the
very beginning, though it doesn't necessarily limit them to values in
the range that particle accelerators can produce.

That doesn't explain why the entropy of the Universe started out as
something less than maximum. The fact that there was a beginning
a finite time ago only explains why the entropy hasn't increased to
maximum since that beginning. It doesn't explain why there was a
beginning with potential to do interesting things afterward.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

I think one problem to keep in mind is that the "laws of physics" should never really be thought of as laws in the grandest sense. You often see questions like "how come the universe doesn't obey this or that law", as if that meant there was something wrong with the universe, instead of a limitation of the law. All laws require simplifying assumptions, and if those assumptions are not in place in the reality, then neither is the "law".

The "laws" of thermodynamics are classic examples, because they are not particularly fundamental laws-- they are more like rules that emerge from the action of the fundamental laws, under certain conditions. Also, sometimes the "laws" are misquoted, or misunderstood. A classic example of all these issues is the second law, that entropy must increase in total in any occurrence that develops spontaneously (i.e., without outside interference). The law does not say "if you wait long enough, you will reach maximum entropy", it just says entropy must increase. And the reason is really quite simple-- what happens spontaneously is whatever is the most likely to happen (it is more likely that a million coins, when flipped, will show a mixture of heads and tails, you have to set them to heads yourself if that's what you want), and whatever is most likely is defined to be the state of highest entropy. However, nowhere in the second law does it mention what configurations the system has access to-- that's something completely different. So the real statement of the law should be that whatever happens is the state of highest entropy that the system has access to given the time allowed and the other constraints in play. In the case of the Big Bang, the universe has simply not had access to higher entropy states.

Why not? Because of gravity, basically. What has been said in the thread so far is true, we don't know what started things off, which is another way of saying we don't know what kinds of constraints the universe was beholden to-- what states it had access to. But it's clear that it only had access to very hot, high density, and dynamical states, and that gravity interacted with that initial condition and told it that it needed to expand. Note that an expanding universe will always exhibit higher entropy, so why doesn't it just expand completely and be done with it? Because it doesn't have access to a complete expansion overnight, it has to obey other laws than just the second law.

That brings in Spaceman Spiff's point that the entropy is increasing, but not as fast as it could be if it were not also constrained by other laws and governed by the expansion that general relativity says it must follow. So the second law is more of an arrow than it is an endpoint-- it says, if you take all the possible behaviors of the universe as a whole, and rank them in order of entropy, the one at the top of the list is what will happen. But that doesn't tell you what's on that list, you have to look at all the other constraints (and laws) to know that. And note that the "laws" themselves will never be enough to do this, because physics always requires that you also specify the "initial conditions" to understand the constraints, and so far there is never a theory that tells you what the initial conditions must be, that does not simply involve other initial conditions.

You might want to take a look at the book The Cosmic Landscape by Leonard Sussking. It discusses his version of the multiverse in quite a bit of detail.

I suggest haveing a large quantity of salt available when you read it. A single grain will be insufficient.

Almost.

If the throw had come up all 6's, the universe would have remained perfectly symmetrical.

Ours didn't. We're a lumpy gravy. As such, one might say that life in the universe is the result of a mistake, of a bad throw of dice.

Oops.

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Ach, mein Sinn, wo willst du endlich hin, wo soll ich mich erquicken? Bleib' ich hier, oder wünsch' ich mir Berg und Hügel auf den Rücken?
Bei der Welt ist gar kein Rat, und im Herzen steh'n die Schmerzen meiner Missetat, weil der Knecht den Herrn verleugnet hat.

Interesting. Does your "personal view" also solve the flatness problem, the lack of observed magnetic monopoles, or predict the (observationally confirmed) spectrum of density perturbations which collapse to form large scale structures such as galaxies and clusters of galaxies? For a more complete overview, you might check the wikipedia entry for cosmic inflation.

Possibly. I've only made an extremely loose connection between my
notion that the creation event is directly responsible for the uniformity
of the Universe, and my notion that the quantity of antimatter in the
Universe is equal to the quantity of ordinary matter. Gravitational
repulsion between the two would give an overall "flat" geometry, and
provide the driving force behind galaxy formation and the acceleration
of the cosmic expansion. I don't have the ability to calculate what
the spectrum of CMBR density perturbations should be, so I can't
test it that way. Another test involves gravitational lensing. I'm
not able to calculate that, either, but it should be easier for me to
do than the spectrum calculations. A third test will be conducted by
CERN in a few years, and will be much more definitive: If antihydrogen
falls up, I'm right; if it falls down, I'm wrong. That should be done by
about 2015, if everything goes as planned.

Oh-- monopoles. I don't see much reason to think that monopoles
are anything real, so I have no reason to explain why they aren't
observed.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

This sounds like it belongs in ATM.

Yes. Except that I don't really have anything more to say about it.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

I tried to keep it simple and used the word "beneficial" to try to cover the quirks. Zero anisotropy would not be beneficial, of course.

Nevertheless, I like your point. Let's say the roll must be 20 6s, 3 5s, and a 1.

__________________
Lighten up! This is a stellar board!

Forgive me but why would we think that matter with a reverse charge would = anti-gravity? Is their an anti particle to the neutron? It has no charge but still has mass. A neutron star still has gravity. I'm not sure why you would tie the electromagnetic charges to gravity.

Wayne,

I don't tie the electric charge to gravity. Although it is fairly common
to read that the only thing which distinguishes antimatter from ordinary
matter is the reversal of electric charges, it is not the only difference.
The two are mirror images of each other. And antimatter looks like
ordinary matter which is time-reversed. This means, for example, that
anti-neutrons *are* different from ordinary neutrons.

My speculation that antimatter has the opposite gravity of ordinary
matter is based on the fact that everything *else* about it is opposite.
Why shouldn't its gravity be opposite, too? We have no direct evidence
that it isn't.

However, the inertial mass of antimatter particles has been long known.
I'm not suggesting that the inertial mass of antimatter is different from
that of ordinary matter-- only the gravitational mass.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

But we have general relativity.
Here's the problem-- photons are their own antimatter. In relativity, gravity is an effect on spacetime, so it cannot be different for matter or antimatter. You can say we don't know if GR is really right when matter and antimatter interact, but we do know it is right for photons-- and photons are their own antiparticle. So I'd say we already do have good evidence that matter cannot gravitationally repel antimatter, unless you throw out both GR and the standard model of particle physics.

I realized the problem with photons about 25 years ago or so. For my idea
to work, photons would have to *not* be their own antiparticle. That's
why the second test I mentioned earlier includes looking for antiphotons
from distant galaxies which have been gravitationally lensed by the gravity
of ordinary matter.

My idea requires no change to general relativity-- only a change in how
general relativity is understood. The story that is told, as you put it.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

Photons are energy, not matter. They don't have an antiparticle, they don't need an antiparticle. In fact, photons are what you get when two matter/antimatter particles annihilate.

Rob

Every kind of matter is energy. Photons are different from most familiar
forms of matter in that they are massless, which is the basis of your
notion that they are energy but not matter. All sorts of particles can
come out of matter/antimatter annihilation. Photons are typical, but
other particle pairs can come out if the original pair provides enough
energy to make them. Note that pair annihilation never produces a
single photon. It always produces at least two photons. I speculate
that one must be an ordinary photon and the other an antiphoton.
I don't know what the differences are or how to tell them apart.

Photons might be their own antiparticles, but they might not be.
I'm betting on the long shot that they are not.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

I can't remember if it was here on BAUT or in one of the Astronomy Cast episodes, but I recall that the reason there are always two (or more) photons created is to conserve momentum. I.e., before the collision the particle/anti-particle are moving towards each other in space at some angle, (head-on being the special case), and so after the collision, the direction vectors of the two particles must be conserved by the resulting photons.

Also, my understanding is that a particle/anti-particle event *always* results in the complete conversion of both into pure energy. At that point, some of that energy can indeed be immediately re-condensed into some other matter/anti-matter particles, which may then annihilate again thus producing more photons that can again re-condense, annihilate, etc, rinse and repeat. But it always starts with the conversion of the original pair into pure energy, not "some energy and some particles."


Rob

Fer sure, momentum is conserved. But the photons don't know that.
They don't know that they need to conserve momentum. So they may
have their own reasons for splitting up that they aren't talking about.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves

robross. Photons are their own anti-particle. Earlier....the antineutron is the anti particle to the neutron. They are both neutral and of equal gravitational/inertial masses. The neutron is two down quarks and an up. The anti-neutron is two anti-down quarks and an anti-up....so if they meet all the quarks annihilate, electric charge disappears...(the quarks carry 1/3 or 2/3 of a unit of charge, so even though the neutron and antineutron are overall uncharged, their constituent quarks are not), color disappears(individual quarks carry color charge, too...with a net of "white "for the three primary color or anti-colors).
There has never been an experiment that showed the gravitational mass to be distinct from the inertial mass, the principle of equivalence and Einstein's GR, and all particles with rest-mass have also a cross section for weak interactions with the neutrino sea that they are born in. Interestingly a recent paper indicated that space is not even defined if there is not a priori a fermionic or bosonic field. Starting with a concept of "empty space" and positing some orthogonal metric rulers to define a Minkowski space-time metric in their view is passe'. Pretty interesting, as it led them to believe it might help in quantum gravity considerations. Authors, Hans Westman and Sebastiano Sonego. pete

see:http://arxiv.org/PS_cache/arxiv/pdf/...711.2651v2.pdf

I'll bet a bowl of jelly beans KenG likes this one.

__________________
A third rate theory forbids.
A second rate theory explains after the fact.
A first rate theory predicts.
A. Lomonosov

Rob,

ALL matter is pure energy. Mass is, in fact, the most dense form of energy
known. I think you meant that pair annihilation turns all the energy into
photons. I think that is always the case when there is not enough energy
to form other massive particles, but not always the case when there *is*
enough energy.

Pete,

While it is true that there has never been an experiment that showed the
gravitational mass of anything to be different from its inertial mass, it is
also true that the gravitational mass of an antineutron has never been
measured. So it is only theory that says its gravitational mass should be
the same as its inertial mass. That theory is based entirely and exclusively
on gravity measurements of ordinary matter.

-- Jeff, in Minneapolis

__________________
http://www.FreeMars.org/jeff/

"I find astronomy very interesting, but I wouldn't if I thought we
were just going to sit here and look." -- "Van Rijn"

"The other planets? Well, they just happen to be there, but the
point of rockets is to explore them!" -- Kai Yeves