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Gary_Glitter
2009-Jul-03, 09:27 AM
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.

astromark
2009-Jul-03, 01:34 PM
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 add:)who 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

antoniseb
2009-Jul-03, 02:45 PM
Law 1 - Energy cannot be created or destroyed
Law 2 - Entrophy increases to a maximum in a sealed system

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

Jeff Root
2009-Jul-03, 03:01 PM
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

thoth II
2009-Jul-03, 03:07 PM
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.

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

Cougar
2009-Jul-03, 03:25 PM
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....

I'd go along with that, although this article by Alan Guth (http://nedwww.ipac.caltech.edu/level5/Guth/Guth3.html) explains a very good possibility that goes back pretty close to the beginning.


....or why the entropy of the Universe is less than maximum.

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....

George
2009-Jul-03, 03:28 PM
Law 1 - Energy cannot be created or destroyed 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.


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? 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".]


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

mugaliens
2009-Jul-03, 03:53 PM
The "Laws" of thermodynamics don't necessarily apply to the entire universe all at once.

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.

Spaceman Spiff
2009-Jul-03, 04:22 PM
Astrophysicist Sean Carroll has a book (http://preposterousuniverse.com/eternitytohere/) coming out in January 2010 on this and related topics. You might also scroll through this list of his postings (http://blogs.discovermagazine.com/cosmicvariance/category/time/) on this and related subjects on the Cosmic Variance blog (http://blogs.discovermagazine.com/cosmicvariance/) (or look at the list of links at the bottom of the first link); this one in particular (http://blogs.discovermagazine.com/cosmicvariance/2007/12/03/arrow-of-time-faq/) 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 (http://en.wikipedia.org/wiki/Conservation_law) have a corresponding statement concerning an important symmetry (http://en.wikipedia.org/wiki/Symmetry_in_physics#Conservation_laws_and_symmetry ) (or an invariance) that describes the universe we live in, a concept formalized by mathematician Emmy Noether (http://en.wikipedia.org/wiki/Noether%27s_theorem) 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 (http://en.wikipedia.org/wiki/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 (http://www.math.ucr.edu/home/baez/physics/Relativity/GR/energy_gr.html); 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.

Gary_Glitter
2009-Jul-03, 07:48 PM
___ 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 add:)who 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

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.

George
2009-Jul-03, 08:14 PM
Thanks for the help so far. Can someone go into more detail about this multiverse you people speak of.
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.

Jeff Root
2009-Jul-03, 08:49 PM
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....
I'd go along with that, although this article by Alan Guth (http://nedwww.ipac.caltech.edu/level5/Guth/Guth3.html) explains a very
good possibility that goes back pretty close to the beginning.
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.




....or why the entropy of the Universe is less than maximum.
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....
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

Ken G
2009-Jul-03, 09:34 PM
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.

DrRocket
2009-Jul-03, 09:50 PM
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.

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.

kleindoofy
2009-Jul-04, 12:15 AM
... 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, ...
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. ;)

matt.o
2009-Jul-04, 01:10 AM
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.

-- Jeff, in Minneapolis

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. (http://en.wikipedia.org/wiki/Cosmic_inflation)

Jeff Root
2009-Jul-04, 01:41 AM
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?
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

matt.o
2009-Jul-04, 01:59 AM
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

This sounds like it belongs in ATM.

Jeff Root
2009-Jul-04, 02:58 AM
Yes. Except that I don't really have anything more to say about it.

-- Jeff, in Minneapolis

George
2009-Jul-04, 03:50 AM
If the throw had come up all 6's, the universe would have remained perfectly symmetrical. 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. :)

WayneFrancis
2009-Jul-06, 02:53 AM
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.

Jeff Root
2009-Jul-06, 07:06 AM
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

Ken G
2009-Jul-06, 08:11 AM
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.But we have general relativity.


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.
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.

Jeff Root
2009-Jul-06, 09:02 AM
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

robross
2009-Jul-06, 09:45 AM
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

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

Jeff Root
2009-Jul-06, 11:16 AM
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

robross
2009-Jul-06, 11:28 AM
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

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

Jeff Root
2009-Jul-06, 11:41 AM
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

trinitree88
2009-Jul-06, 04:34 PM
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

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/0711/0711.2651v2.pdf

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

Jeff Root
2009-Jul-06, 07:19 PM
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

Ken G
2009-Jul-06, 09:58 PM
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.
Not quite, it is also based on gravity measurements on photons. Photons are not ordinary matter, and indeed their behavior is used to bolster our confidence in general relativity (which in turn predicts matter and antimatter fall the same). In particular, our understanding of matter and antimatter is that photons are their own antiparticle, and that is more or less verified by experiment. So since all photons "fall the same way", we have an observed example of antimatter that obeys general relativity, in contradiction to your claim above.

Jeff Root
2009-Jul-08, 07:38 AM
Okay, Ken. You have suggested a fourth test of my idea. I need to find
out if something like the Pound-Rebka experiment has been done with light
that comes from a source involving antimatter. If it has, the experimenters
probably deliberately looked for possible differences between ordinary
photons and antiphotons. Even if they didn't deliberately look for such
differences, they probably would have seen any differences if they existed.
If no such experiment has been done, I have to figure out how to do it.

Why do all these experiments have to be so extremely delicate? :p

-- Jeff, in Minneapolis

ToeQuestor
2009-Jul-08, 08:58 AM
Some thoughts about entropy gathered from reading Stenger…

If the design of the universe was inserted at its creation, we should expect to see some degree of order possessed at that zero-time.This expectation of order is often expressed in terms of the 2nd law of thermodynamics: the total entropy or disorder of a closed system must either remain constant or increase with time. Now, was the universe always a closed system or was order imparted from the outside at the beginning?

Prior to 1929, the ‘necessary’ outside influence was a strong argument for a miraculous creation. Then this [stock-market of an] idea crashed, for Hubble discovered that the universe is expanding, the galaxies moving away from each other. Thus, an expanding universe could have started in total chaos and still formed localized order consistent with the 2nd law. But, did it?

Due to this 2nd law, the total entropy of the universe must increase as the universe expands; however, the maximum possible entropy increases even faster, leaving increasingly more room for order to form. The reason is that the maximum entropy is that of a black hole. The expanding universe is not a black hole.

Back at the earliest definable moment, the Planck time, the universe was confined to the smallest definable region of space, it having the radius of the Planck length [not a singularity]. As must be the case, the universe at that time had lower entropy that it has now; however, that entropy was as high as it possibly could have been for an object that small. Note that this is because a sphere of Planck dimensions is equivalent to a black hole, from which no information can be extracted.

How is it, then that this ‘maximal’ entropy when the universe began can be ever increasing ever since? It is because the entropy of the universe now is higher for its current size, but not maximal, as said, since it is no longer a black hole.

Also, remember that there is no time interval that can be defined that is smaller than the Planck time. This is implied by Heisenburg’s uncertainty principle, again showing that no information can escape. Thus, there is no need for a theory of quantum gravity to describe the physics earlier than the Planck time.

The definition of time is: that which is counted off as an integral number of units of the Planck time. This is discrete, but we can, as in calculus, treat it as continuous in mathematical physics since the units are small compared to anything we measure in practice.

So, we extrapolate through the Planck intervals. Because we can do it ‘now’, we can do it at the earliest Planck interval where the big bang’s description begins. At that time, the disorder was complete; it was maximal.

Thus the universe began with no structure. The universe has structure today since its entropy is no longer maximal.

The universe thus began with no organization, either designed or otherwise. [In fact it was chaos!]

There was no initial design built in to the universe at its beginning!

Ken G
2009-Jul-08, 01:19 PM
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.
Again I must point out that is false. Photons are not ordinary matter, indeed they are their own antiparticles. So if you want antineutrons to fall the other way, you'll need a very bizarre theory that has massless antipartlcles fall the same way, but antiparticles with rest mass fall the other way. So the limiting behavior as the mass of a hypothetical antineutrino goes to zero would have to suddenly change, even though the motion under gravity will not depend on the mass as the mass gets smaller.

Jeff Root
2009-Jul-08, 01:41 PM
No, that's completely out. If antimatter has opposite gravity of ordinary
matter, then the photon can't be its own antiparticle. Can you point out
to me any observations which show the photon to be its own antiparticle?

Note that the second test I mentioned earlier also includes the response
of antiphotons to gravity (as well as ordinary photons to antigravity).
The second test looks for gravitational lensing; the test you suggested
looks for gravitational frequency shifts. Like measuring the fall (or rise)
of antihydrogen in Earth's gravity, measuring frequency shifts would be
exceedingly difficult.

-- Jeff, in Minneapolis

Ken G
2009-Jul-08, 01:45 PM
No, that's completely out. If antimatter has opposite gravity of ordinary
matter, then the photon can't be its own antiparticle. Can you point out
to me any observations which show the photon to be its own antiparticle?

No observation can establish that, the concept of antimatter is a theoretical distinction. But yes, the entire theory of antimatter establishes the photon as its own antiparticle, because that theory unifies observations like proton plus antiproton annihilates into two photons, and vice versa. If antiprotons fall the other way, many of the current successes of particle physics, and several useful conservation laws, would need to be thrown out. That doesn't make it impossible, but it means there is no good reason to think that antiprotons will fall the other way.

Jeff Root
2009-Jul-08, 02:05 PM
I see no reason why the two photons produced in proton-antiproton
annihilation could not be mirror images of each other: ordinary photon
and antiphoton. I do not see anything that would have to be thrown
out except the theoretical idea that the photon is its own antiparticle.

Specifically what do you think would have to be thrown out?

-- Jeff, in Minneapolis

Ken G
2009-Jul-08, 02:34 PM
I see no reason why the two photons produced in proton-antiproton
annihilation could not be mirror images of each other: ordinary photon
and antiphoton. They both fall the same way, so your two propositions are now internally inconsistent.

Specifically what do you think would have to be thrown out?
The very normal proposition that particles that are identical in every way can be called "identical particles".

Jeff Root
2009-Jul-08, 03:27 PM
What observations do you know of that show the response of photons
originating in proton-antproton annihilation to gravity? You say that they
both fall the same way. I say that you don't know which way they fall
because it has never been observed.

You don't know that the photons originating in proton-antiproton
annihilation are identical in every way. That is an assumption based
primarily on the fact that no differences have yet been observed.
If antimatter-- including antiphotons-- is repelled by ordinary gravity,
that will be very difficult to observe. If it isn't repelled by ordinary
gravity, that will be very difficult to observe, too. But one way or the
other, the observation will either verify or disprove my speculation.
If the observations are conclusive, so will be the consequences for
my speculation. But, to the best of my knowledge, you have no more
observations supporting your contention than I have supporting mine.

-- Jeff, in Minneapolis

trinitree88
2009-Jul-08, 03:43 PM
What observations do you know of that show the response of photons
originating in proton-antproton annihilation to gravity? You say that they
both fall the same way. I say that you don't know which way they fall
because it has never been observed.

You don't know that the photons originating in proton-antiproton
annihilation are identical in every way. That is an assumption based
primarily on the fact that no differences have yet been observed.
If antimatter-- including antiphotons-- is repelled by ordinary gravity,
that will be very difficult to observe. If it isn't repelled by ordinary
gravity, that will be very difficult to observe, too. But one way or the
other, the observation will either verify or disprove my speculation.
If the observations are conclusive, so will be the consequences for
my speculation. But, to the best of my knowledge, you have no more
observations supporting your contention than I have supporting mine.

-- Jeff, in Minneapolis
Jeff. The inertial mass of the antiproton has been experimentally found to be identical to the proton to four parts in 108. Are you asserting that though these are identical, the gravitational interaction is asymmetric? What about their neutral current cross-sections, are these inverted also? There is no precedent here. pete see:http://www.iop.org/EJ/abstract/1402-4896/46/3/010

Ken G
2009-Jul-08, 03:45 PM
What observations do you know of that show the response of photons
originating in proton-antproton annihilation to gravity? You say that they
both fall the same way. I say that you don't know which way they fall
because it has never been observed.Let me get this straight. You are saying that there might be two types of photons that are not distinguishable in any way that has ever been observed, but they will turn out to fall in different directions if we ever have the ability to observe lensing or gravitational deflection of these "anti-photons"? It is true that such photons would have to originate at high energies (above 511 keV for electron-positron annihilation), so even if highly redshifted would still be X-rays. Gravitational lensing of X-rays has been seen, but not hard X-rays, so there are probably not observations that rule out anti-photons that fall the other way.

There are also no observations that rule out unicorns, or invisible faeries. The real question is, are there any observations that suggest their existence? Is there any general theoretical framework that does a better job of unifying what we see than the current understanding of matter and antimatter, by which photons and anti-photons are identical? And is there any reason to think that two massless particles can do two different things, when the beautifully unifying theory of GR says that it would be impossible for two massless particles to do two different things? (For example, you would have to throw out relativity and our current understanding of causality.) No, there is no justification for any such expectation. We don't know that antiphotons are identical to photons, and we don't know that invisible unicorns are not prancing among us even now.


You don't know that the photons originating in proton-antiproton
annihilation are identical in every way. We know that no observational differences between them have ever been found. That's called science. It is called something else to say "ahh, but they could still be different, so I'm going to choose to believe they are." You are certainly welcome to your own personal beliefs, but it will make a very short ATM thread: "No one has ever looked for invisible unicorns at ultra-low levels of gamma-ray radiation, so I predict that if we could see ultra-low levels of gamma radiation, we would detect the presence of invisible unicorns." Not much to say there, either.


That is an assumption based
primarily on the fact that no differences have yet been observed.Precisely.


If antimatter-- including antiphotons-- is repelled by ordinary gravity,
that will be very difficult to observe.Yes, as difficult as invisible unicorns.


But one way or the other, the observation will either verify or disprove my speculation.As would looking for the gamma-ray signature of my invisible unicorns. The question is not "what observation can falsify my claim", it is, "what basis does my claim actually have, given that there is zero evidence for it, and it would undo other theories that have worked great, like relativity and causality."

Jeff Root
2009-Jul-08, 04:12 PM
The inertial mass of the antiproton has been experimentally found
to be identical to the proton to four parts in 108. Are you asserting
that though these are identical, the gravitational interaction is
asymmetric?
Speculating and hypothesizing that they are asymmetric, yes. The
inertial mass would be the absolute value of the gravitational mass.



What about their neutral current cross-sections, are these
inverted also?
I don't know. I'll study that.

Editing to add:

In light of what I say to Ken, below, I shouldn't have agreed that I
suspect the gravitational interaction is "asymmetric". Instead I should
have said that I suspect it is symmetric. Mirror image. An unbroken
symmetry. Equal and opposite.

-- Jeff, in Minneapolis

Jeff Root
2009-Jul-08, 05:09 PM
Let me get this straight. You are saying that there might be two types
of photons that are not distinguishable in any way that has ever been
observed, but they will turn out to fall in different directions if we ever
have the ability to observe lensing or gravitational deflection of these
"anti-photons"?
Yes.

That surprised me when I realized it some 25 years ago, but it is
obviously necessary if antimatter has gravity opposite to ordinary
matter, since we know that ordinary photons are affected in the
ordinary way by ordinary gravity.



It is true that such photons would have to originate at high energies
(above 511 keV for electron-positron annihilation), so even if highly
redshifted would still be X-rays. Gravitational lensing of X-rays has
been seen, but not hard X-rays, so there are probably not observations
that rule out anti-photons that fall the other way.

There are also no observations that rule out unicorns, or invisible faeries.
The real question is, are there any observations that suggest
their existence? Is there any general theoretical framework that does a
better job of unifying what we see than the current understanding of
matter and antimatter, by which photons and anti-photons are identical?
I don't have a theory-- only conjecture. The bases of my conjecture
are the similarities between the fundamental forces, and the symmetries
underlying the conservation laws. I speculate that gravity is like the
electric force in having both positive and negative "charges", in exactly
equal amounts. I speculate that the amounts of ordinary matter and
antimatter which came out of the Big Bang were exactly equal, since
no mechanism has been proposed which could create them in unequal
amounts, and they have never been observed to be created in anything
except precisely equal amounts. I speculate that the repulsive force
of gravity was the driving force initiating the collapse of matter into
galaxies, and is now the force pushing clusters of galaxies apart,
accelerating the cosmic expansion. The equal quantities of opposite
gravitational mass would explain the overall "flatness" of the Universe.
It might eliminate the need for Inflation.



And is there any reason to think that two massless particles can do
two different things, when the beautifully unifying theory of GR says
that it would be impossible for two massless particles to do two different
things? (For example, you would have to throw out relativity and our
current understanding of causality.)
I do not see any conflict with either relativity or causality. As I said
in an earlier post, the interpretation of relativity's "story" would need
to change, but relativity theory itself would require no change at all.
(The change in the "story" is simply an extension of the principle of
equivalence to include negative values as well as positive and zero
values for mass.) I don't have any idea what conflict you see with
causality. What conflict do you see?



No, there is no justification for any such expectation. We don't know
that antiphotons are identical to photons, and we don't know that
invisible unicorns are not prancing among us even now.
I suspect that antiphotons are different from photons. We have at
least two different ways to determine whether they are or are not
different. Each will be conclusive if the observations are conclusive.
In addition, we can measure the response of antihydrogen to gravity.
That determination will also be conclusive if the observations are.

-- Jeff, in Minneapolis

Ken G
2009-Jul-08, 10:45 PM
The bases of my conjecture
are the similarities between the fundamental forces, and the symmetries
underlying the conservation laws. I speculate that gravity is like the
electric force in having both positive and negative "charges", in exactly
equal amounts. The main problem with this is that it violates the equivalence principle, so it undoes general relativity. That is a big problem, so requires observational support, but there is none. It is possible to take any theory and come up with some situation that has not yet been observed, and speculate that some different result will occur in that situation. What does such speculation gain us? We always want to check our theories in new situations, it doesn't add anything to speculate a different outcome unless it comes with a competing theory that has various other advantages. That's the problem with speculating that invisible unicorns emit a spectrum of ultra-low intensity gamma rays, that we can only detect if our instruments get more sensitive.


I speculate that the repulsive force
of gravity was the driving force initiating the collapse of matter into
galaxies, and is now the force pushing clusters of galaxies apart,
accelerating the cosmic expansion. The equal quantities of opposite
gravitational mass would explain the overall "flatness" of the Universe.
It might eliminate the need for Inflation.You'd still need inflation, because you not only need a rapid expansion, you also need a way to turn it off very suddenly and very early on. Inflation is believed to have been caused (if it happened at all) by a negative gravity, that is already the model. But it is a phase change that happened at a certain (very high) temperature, so there was a way to turn it off. Your picture would not be able to turn off, it would be inflation that continued. You would have way too much expansion at early times, the times when nucleosynthesis was creating the helium we see now. It is quite important that there not be any kind of inflation during those minutes, or we'd have way less helium than we do.

Certainly, the possibility that there is an equal amount of antimatter has been considered, and is generally ruled out on the grounds that we'd see emission from the boundaries between the two, which we do not see. I think the most popular resolutions are that there was either a spontaneous breaking of the matter/antimatter symmetry (on the grounds that all symmetries are basically made to be broken), or that the regions where there was antimatter got inflated to unobservable distances from us.

I do not see any conflict with either relativity or causality. There is a huge conflict with both relativity and causality. The conflict with (general) relativity is that you'd have to throw out the equivalence principle, so that principle would have to be some kind of bizarre coincidence that only appears to apply to matter, and gravity would not be interpretable as a geometric effect. It would also do violence to causality, because it is a straightforward theorem of causality that all massless particles have to do the same thing, or else you cannot tell which events are timelike versus spacelike separated. Currently, if you can send a light signal between two events, you have an absolute time sequence and a potential causality between those events, and if you cannot, then you don't. But if "antilight" signals connect events that light signals don't, causality is massacred. You have different causal connection between matter and antimatter than you have between matter alone, yet matter and antimatter interact via the fundamental forces.

For example, you'd have particles annihilating inside the event horizons of black holes, and sending out antilight that does escape the black hole and can be seen at Earth. Not only is that not observed, but it would violate our current conception of causality and event horizons. Basically, antimatter would require a second spacetime, yet would have to be able to interact with normal matter.


(The change in the "story" is simply an extension of the principle of
equivalence to include negative values as well as positive and zero
values for mass.) No, you cannot "extend" the equivalence principle like that. There would be no equivalence principle at all-- if you were in a box and matter and antimatter accelerated different ways, you would know it was gravity, and if they went the same way, you'd know your box was accelerating. You see, the whole point of the equivalence principle is that it explains why gravitational mass is the same as inertial mass, but you have them differing in sign for antimatter.

Jeff Root
2009-Jul-09, 06:59 AM
The bases of my conjecture are the similarities between the
fundamental forces, and the symmetries underlying the conservation
laws. I speculate that gravity is like the electric force in having both
positive and negative "charges", in exactly equal amounts.
The main problem with this is that it violates the equivalence principle,
so it undoes general relativity.
It only violates your interpretation of the equivalence principle.

Here is a law of nature that has been demonstrated for centuries:

Electrically-charged bodies always repel one another by the electric
force. You agree with that, don't you? Bring two charged bodies
close together, and they repel each another.

Of course, here on the planet Primrose, there aren't enough negative
electric charges in the whole world to give any body a measureable
negative charge, so all measurements are necessarily done using the
wonderful positive charges that we have in abundance. But they
consistently show that charged bodies always repel, so this must be
true when negatively-charged bodies are involved, too.

The equivalence principle was developed from measurements of
ordinary matter exclusively. It describes the behavior of ordinary
matter perfectly.

Your interpretaion needs to allow mass to have negative values as
well as positive and zero values. General relativity itself does not
restrict the values, so there is no actual problem.



That is a big problem, so requires observational support, but there
is none. It is possible to take any theory and come up with some
situation that has not yet been observed, and speculate that some
different result will occur in that situation. What does such
speculation gain us? We always want to check our theories in new
situations, it doesn't add anything to speculate a different outcome
unless it comes with a competing theory that has various other
advantages.
:D




I speculate that the repulsive force of gravity was the driving force
initiating the collapse of matter into galaxies, and is now the force
pushing clusters of galaxies apart, accelerating the cosmic expansion.
The equal quantities of opposite gravitational mass would explain the
overall "flatness" of the Universe. It might eliminate the need for
Inflation.
You'd still need inflation, because you not only need a rapid expansion,
you also need a way to turn it off very suddenly and very early on.
Inflation is believed to have been caused (if it happened at all) by a
negative gravity, that is already the model. But it is a phase change
that happened at a certain (very high) temperature, so there was a
way to turn it off. Your picture would not be able to turn off, it would
be inflation that continued. You would have way too much expansion
at early times, the times when nucleosynthesis was creating the helium
we see now. It is quite important that there not be any kind of inflation
during those minutes, or we'd have way less helium than we do.
Nothing like any of that.

I said that the equal quantities of opposite gravitational mass might
eliminate the need for Inflation, not that it would provide a mechanism
for Inflation.

Inflation was hypothesized primarily to explain the large-scale isotropy
and flatness of the Universe. Inflation explains the isotropy as a result
of a small isotropic region inflating into an enormous isotropic region.
That inflation is not needed. Whatever caused the Big Bang caused
the isotropy.

All the matter/energy participating in the cosmic expansion was once
in causal contact. If it were not, it could not be participating in the
expansion.

The creation must have taken some time to occur. At the end of that
period the Universe was very dense, hot, homogenous and isotropic,
and expanding uniformly. Its uniformity resulted from the creation of
all the matter/energy by the same mechanism, whatever it was.
There could not be any non-uniformities that needed evening out.

The flatness of the Universe would be the unavoidable consequence
of exactly equal quantities of positive and negative gravitational mass.
It would naturally be flat at all times.

So there is no need for inflation, and no inflation to stop.

The expansion caused by matter-antimatter gravitational repulsion
would not have begun until massive particles stopped being converted
into light by high-energy collisions. Most of the matter and antimatter
mutually annihilated, but wherever there was an excess of one over the
the other, it survived and was separated from its counterpart. As the
regions of matter and antimatter move farther and farther apart from
each other, the repulsive force between them grows weaker, so the
acceleration of the expansion diminishes with time.

This is just a crude illustration: Expansion history of the Universe (http://www.freemars.org/jeff/misc/cosmolog/expansn1.png)



Certainly, the possibility that there is an equal amount of antimatter
has been considered, and is generally ruled out on the grounds that
we'd see emission from the boundaries between the two, which we do
not see.
The ordinary matter and antimatter would have repelled each other
most strongly at the outer edges of their respective regions. Direct
contact between regions would have ended at the same time as the
regions became distinct.



I think the most popular resolutions are that there was either a
spontaneous breaking of the matter/antimatter symmetry (on the
grounds that all symmetries are basically made to be broken),
My fundamental notion is that the symmetries are unbroken.



or that the regions where there was antimatter got inflated to
unobservable distances from us.
I hypothesize that half of all the galaxies we see are antimatter.
They just haven't been recognized as such, yet.



There is a huge conflict with both relativity and causality. The
conflict with (general) relativity is that you'd have to throw out
the equivalence principle, so that principle would have to be some
kind of bizarre coincidence that only appears to apply to matter,
and gravity would not be interpretable as a geometric effect.
There is no conflict with the equivalence principle. The equivalence
principle is general enough to handle the concept of negative mass,
without any alteration. General relativity would require no alteration.
There is no coincidence involved, and gravity can still be interpreted
as a geometric effect.



It would also do violence to causality, because it is a straightforward
theorem of causality that all massless particles have to do the same
thing, or else you cannot tell which events are timelike versus spacelike
separated. Currently, if you can send a light signal between two events,
you have an absolute time sequence and a potential causality between
those events, and if you cannot, then you don't. But if "antilight" signals
connect events that light signals don't, causality is massacred. You
have different causal connection between matter and antimatter than
you have between matter alone, yet matter and antimatter interact via
the fundamental forces.

For example, you'd have particles annihilating inside the event horizons
of black holes, and sending out antilight that does escape the black hole
and can be seen at Earth. Not only is that not observed, but it would
violate our current conception of causality and event horizons.
I wouldn't expect such a thing to be observed: our telescopes are not
powerful enough to do that. But the theoretical consideration seems
reasonable. It looks like it might be a logical contradiction. I'll have
to think about it.

However, as an off-the-top-of-my-head response, I'll point out that
the description of causality you are using is built on the assumption
that gravity is always attractive. If we drop that assumption, then
your description of causality may need to change, too. In which case
causality would not be violated because causality is something slightly
different from what you are currently assuming it is.



Basically, antimatter would require a second spacetime, yet would
have to be able to interact with normal matter.
No-- no "second spacetime". Antigravity would warp spacetime
oppositely to ordinary gravity, but it would be the same spacetime.




(The change in the "story" is simply an extension of the principle of
equivalence to include negative values as well as positive and zero
values for mass.)
No, you cannot "extend" the equivalence principle like that. There
would be no equivalence principle at all-- if you were in a box and
matter and antimatter accelerated different ways, you would know
it was gravity, and if they went the same way, you'd know your box
was accelerating. You see, the whole point of the equivalence
principle is that it explains why gravitational mass is the same as
inertial mass, but you have them differing in sign for antimatter.
Yes. I'm speculating that inertial mass is the absolute value of
gravitational mass. If you only study the gravity of ordinary matter,
never the gravity of antimatter, you might think that inertial mass is
the same as gravitational mass. Someone in an antimatter galaxy
who only studies the gravity of antimatter, never the gravity of
ordinary matter, might likewise think that inertial mass is the same
as gravitational mass. If inertial mass is the absolute value of
gravitational mass, the equivalence is lost, but a deeper equivalence
is retained, without any alteration of the theory of relativity. Yes,
by having both ordinary matter and antimatter, you'd be able to
tell the difference between gravity and acceleration. The principle
of equivalence is only a crude approximation anyway. In real cases,
it isn't hard to tell which is actually occurring. And that does not
interfere with the validity of the princple of equivalence or the
validity of general relativity.

A lump of ordinary matter in a box is forced against the floor of the
box equally by ordinary gravity or by accelerating the box "upward".

A lump of antimatter in a box is forced against the floor of the box
equally by antigravity or by accelerating the box "upward".

A lump of ordinary matter in a box is forced against the ceiling of
the box equally by antigravity or by accelerating the box "downward".

A lump of antimatter in a box is forced against the ceiling of the box
equally by ordinary gravity or by accelerating the box "downward".

Completely symmetrical behavior.

-- Jeff, in Minneapolis

ToeQuestor
2009-Jul-09, 07:58 AM
Any comments about my entropy post up towards the top of the page?

Ken G
2009-Jul-09, 01:07 PM
It only violates your interpretation of the equivalence principle.
I wish! No, I'm afraid the credit for that goes to Albert Einstein. From the Wiki on equivalence principle:
"we [...] assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system." (Einstein 1907)

What part of the words "complete physical equivalence" are you attributing to "my interpretation"? That was a simply absurd claim. And your idea that the principle is not violated is equally absurd-- because none of the cases you supply has both matter and antimatter inside the box at the same time. As I said above, that would allow us to differentiate gravity from acceleration, quite obviously there is no equivalence principle in that situation.

Your speculation is pointless because it violates general relativity, and it has no observational support whatsoever. It also has no theoretical support, because it is not part of any theory that has any advantages over the current ones. None of that makes it wrong (it just makes it no better than speculating gamma-ray emitting invisible unicorns), but what does make it wrong is this: it is contraindicated by the fact that black holes are not extremely bright as super-high temperatures are encountered by the material falling in. Those super-high temperatures would cause the creation of particles and antiparticles, in equal measure, and the antiparticles would escape. That would in turn create very bright, high-energy emissions that we do not see.

Ken G
2009-Jul-09, 01:27 PM
Any comments about my entropy post up towards the top of the page?What you said is a fairly standard interpretation of thermodynamics, so it all seemed reasonable, except for the most crucial issue of all: does the fact that the universe was expanding at the Planck time (assuming our model can go back that far) violate the condition that the entropy was maximal for its size? That isn't clear to me, and I'm not sure there is even a known answer to that. There are some ideas about how to incorporate entropy into general relativity (black-hole entropy a la Hawking), but I don't know if there is a uniformly consistent theory for extending that to cosmology. Interesting question, I couldn't say. But even if the disorder was maximal, I'm not sure what that says vis a vis a need for something external to the system-- other things than just "order" can be pointed to as evidence for some "initial openness" in the universe. I don't think the whole concept of "open versus closed" can be meaningfully extended to the other common concept of "initial conditions", because the former is only defined subsequent to the latter.

George
2009-Jul-09, 05:14 PM
I don't think the whole concept of "open versus closed" can be meaningfully extended to the other common concept of "initial conditions", because the former is only defined subsequent to the latter. Or "ladder", since none seem capable of reaching that last turtle. :)

Ken G
2009-Jul-09, 07:04 PM
Quite so!

trinitree88
2009-Jul-09, 08:31 PM
Speculating and hypothesizing that they are asymmetric, yes. The
inertial mass would be the absolute value of the gravitational mass.


I don't know. I'll study that.

Editing to add:

In light of what I say to Ken, below, I shouldn't have agreed that I
suspect the gravitational interaction is "asymmetric". Instead I should
have said that I suspect it is symmetric. Mirror image. An unbroken
symmetry. Equal and opposite.

-- Jeff, in Minneapolis

Jeff. Actually mirror images have a broken symmetry in that they are chiral or handed...left and right, like asymmetric carbon atoms in optical isomerism.

see:http://en.wikipedia.org/wiki/Diastereomer

see:http://en.wikipedia.org/wiki/Chirality_(chemistry)

Jeff Root
2009-Jul-10, 02:14 AM
Jeff. Actually mirror images have a broken symmetry in that they are
chiral or handed...left and right, like asymmetric carbon atoms in optical
isomerism.
One of us doesn't understand what the other is saying.

I'm saying that the two things are mirrors images of each other, so
that there is a perfect symmetry between them.

Anything that has "chirality", or "handedness" is asymmetrical, of
course. But it and its mirror image together are perfectly symmetrical.

Does that make sense? Is what you pointed out irrelevant to what I
was saying, or have I failed to understand your point?

(Your second link doesn't find the page unless the symmetry is fixed
by repositioning the closing parenthesis to inside the closing tag.)

http://en.wikipedia.org/wiki/Chirality_(chemistry)

-- Jeff, in Minneapolis

trinitree88
2009-Jul-10, 03:19 PM
One of us doesn't understand what the other is saying.

I'm saying that the two things are mirrors images of each other, so
that there is a perfect symmetry between them.

Anything that has "chirality", or "handedness" is asymmetrical, of
course. But it and its mirror image together are perfectly symmetrical.

Does that make sense? Is what you pointed out irrelevant to what I
was saying, or have I failed to understand your point?

(Your second link doesn't find the page unless the symmetry is fixed
by repositioning the closing parenthesis to inside the closing tag.)

http://en.wikipedia.org/wiki/Chirality_(chemistry)

-- Jeff, in Minneapolis


Jeff I think in the case of kaons and the Tau-Theta puzzle, the image and the mirror image are not symmetric, which is what the puzzle was. pete

see:http://en.wikipedia.org/wiki/Parity_(physics)

see also:http://ccreweb.org/documents/parity/parity.html#Conclusion