How is space expanding ?

[BlackHole]

Many physicists start to believe that cosmic inflation can explain the acceleration without the need for dark energy. Other believe it's an experimental error.

 

Viable exact model universe without dark energy from primordial inflation

David L. Wiltshire

 

http://www.arxiv.org/abs/gr-qc/0503099

 

Primordial inflation explains why the universe is accelerating today

 

http://arxiv.org/hep-th/0503117

 

Effect of inhomogeneities on the expansion rate of the Universe

 

http://arxiv.org/hep-ph/0409038

 

The Effect of Inhomogeneities on the Luminosity Distance-Redshift Relation: is Dark Energy Necessary in a Perturbed Universe?

 

http://arxiv.org/abs/astro-ph/0501152

 

Exact model universe fits type IA supernovae data with no cosmic acceleration

 

http://www.arxiv.org/abs/astro-ph/0504192

 

Primordial inflation explains why the universe is accelerating today

 

http://arxiv.org/hep-th/0503117

 

Do Large-Scale Inhomogeneities Explain Away Dark Energy?

 

http://arxiv.org/abs/astro-ph/0503553

 

Can superhorizon cosmological perturbations explain the acceleration of the universe?

 

http://arxiv.org/abs/astro-ph/0503582

 

Here's a paper by Halton Arp:

 

The Discovery of a High Redshift X-ray Emitting QSO Very Close to the Nucleus of NGC 7319

 

http://arxiv.org/abs/astro-ph/0409215

[island]

Martin and island' date=' communication between different people with different science knowledge, using advanced scientific words, in a for me foreign language, is not easy...

 

island, I apologize again for misinterpreting Your posts.

 

I have reread all island's posts in this thread and I still have trouble "connecting" them with Martin's view, maybe it's because Martin take a more common approach and island specific stick to Ned Wright's or I am still not able to understand island. (or misinterpret Martin also)

 

To clearify which is which I will try to show, how I perceive, the differences:

 

island view) Vacuum energy, vacuum have gravity which pushes bodies apart, the speed due to the push is not exceeding light but the creation of new vacuum causes that, important is that the push cancels out the normal grip of gravity between the bodies, energy don't have to be conserved since new energy is inserted from the vacuum.

 

Martin view) Inertia, the metric is changing and nothing moves, energy is conserved by also streaching gravity together with space, the gravitational energy between the objects being streached apart is constant, so gravity is sort of "amplified" relative the metric with the same rate as expansion.

 

So am I right or wrong ? Both views explains the missing "grip" but are not exactly the same.[/quote']

 

No apologizing necessary Spyguy... I'm not ignoring you, I've just been busy and I'm at a loss as to how I might explain it any better. Frankly, I don't necessarily dissagree with your point.

 

I was cheating by using new physics to *try* to explain it by adding a cosmological term to the field equations in a closed *expanding* universe, which is different than the commonly projected open expanding universe where Martin is coming from.

 

Not that the new physics is wrong, because you can pull it right out of the information on Ned's site, but the answer that I keep coming back to doesn't fit the accepted explanation, because it indicates that there is an increase in the pressure differential beween matter and the vacuum that occurs when you increase negative vacuum pressure.

 

The Friedman equations give the time evolution and geometry of the universe as a function of the fluid density, which is an acceleration equation, so... I dunno.

[Martin]

... I'm at a loss as to how I might explain it any better. ...

 

 

I also am momentarily at a loss. Spyman did you read the recent Sci Am article by Lineweaver and Davis?

You probably should read it all thru. or anyway if you did we might have clear things online to point to and ask about and discuss.

 

I saw the article online. Let me see if I can get a link, and if the link still works

 

Here,

... Lineweaver and Davis article in March 2005 SciAm

http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0009F0CA-C523-1213-852383414B7F0147

 

this was a feature article "Misconceptions about BigBang"

It had some sidebars which were pictorial diagrams with a question together with right and wrong answers explained.

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p39.gif

What kind of explosion was the big bang?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p40.gif

Can galaxies recede faster than light?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p42.gif

Can we see galaxies receding faster than light?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p43.gif

Why is there a cosmic redshift?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p44.gif

How large is the observable universe?

 

http://www.sciam.com/media/inline/0009F0CA-C523-1213-852383414B7F0147_p45.gif

Do objects inside the universe expand, too?

[Martin]

Charles Lineweaver and Ned Wright are both pure mainstream worldclass working cosmologists

 

Wright is principle investigator for the WMAP satellite studying CMB

Lineweaver was principle investigator for the COBE satellite that studied the CMB in the 80s and 90s

 

i.e. they have been leaders in the two of the projects that have generated the biggest news in cosmology for 10-15 years (also to be mentioned would be the "Hubble key project" accurately establishing the value of the Hubble parameter, and the type IA supernovae observations detecting acceleration)

 

whatever marginal NON-mainstream stuff you look at, Spyman, you should try to understand the consensus picture in mainstream cosmology. It is the standard picture that you need to have to compare the others (like in Blackhole posts, the David Wiltshire "no dark energy needed" and the Halton Arp "they deny me telescope time because they'r afraid I will prove my theory" and so on). Some of the eccentrics could well be right and the current majority consensus could be wrong!! But you need to learn the majority view at least as a point of reference.

 

So if island says go look at Ned Wright, and you like his style (as I do also) then study it! Wright teaches Cosmology at UCLA and has a world reputation and is reputable as hell and has responsibility for major projects.

Lineweaver is likewise respectable and gives the straight dope (mainstream version) and he has this recent Sci Am article also. And they both tell the same story.

 

Maybe I already recommended you read the Lineweaver article and you already did and I forgot, but if you havent already, please do and then we have something to discuss. A little grit on the road for traction

[island]

Ned is a really brite guy that used to hang out in the physics research group... before some of the people in this forum were born... LOL... *ouch*

[island]

Spyman did you read the recent Sci Am article by Lineweaver and Davis?

 

I guess that everyone has their own theoretical prejudice' date=' but they really shouldn't push unproven cutting-edge theory as the mainstream approach:

 

From that article:

[i']Cosmologists sometimes state that the universe used to be the size of a grapefruit, but what they mean is that the part of the universe we can now see--our observable universe--used to be the size of a grapefruit.[/i]

 

*cough*... no that's wrong, at least, in terms of "mainstream physics" anyway... and any good theoretical physicist will tell you that GR with a cosmological constant is still the best/most-conservative way to explain an accelerating expanding universe.

 

If the structure of the universe is governed by general relativity, then the universe must necessarily be spherical, finite, and closed.

 

I don't know about you guys, but I REALLY like that!... and so did Einstein, as it turns out. Dr. Einstein always went for the solution that was "closest at hand"... meaning the simplist explanation in context

 

There is good reason for that, as Occam pointed out, and my understanding is that "convenience" and "simplicity" are the most natural approach for a very fundamental reason... e.g., parameterized energy efficiency... which is what the entropy of the universe is all about, in terms of its most predominant effort to achieve absolute thermal equilbrium within the constraints of inherent imperfection.

 

The shortest path... in context

[Johnny5]

I guess that everyone has their own theoretical prejudice' date=' but they really shouldn't push unproven cutting-edge theory as the mainstream approach:

 

From that article:

[i']Cosmologists sometimes state that the universe used to be the size of a grapefruit, but what they mean is that the part of the universe we can now see--our observable universe--used to be the size of a grapefruit.[/i]

 

*cough*... no that's wrong, at least, in terms of "mainstream physics" anyway... and any good theoretical physicist will tell you that GR with a cosmological constant is still the best/most-conservative way to explain an accelerating expanding universe.

 

If the structure of the universe is governed by general relativity, then the universe must necessarily be spherical, finite, and closed.

 

I don't know about you guys, but I REALLY like that!... and so did Einstein, as it turns out. Dr. Einstein always went for the solution that was "closest at hand"... meaning the simplist explanation in context

 

There is good reason for that, as Occam pointed out, and my understanding is that "convenience" and "simplicity" are the most natural approach for a very fundamental reason... e.g., parameterized energy efficiency... which is what the entropy of the universe is all about, in terms of its most predominant effort to achieve absolute thermal equilbrium within the constraints of inherent imperfection.

 

The shortest path... in context

 

Quick question...

 

Is, or can General relativity agree with the idea that photons mediate the gravitational force? Yes or no?

[Martin]

I guess that everyone has their own theoretical prejudice' date=' but they really shouldn't push unproven cutting-edge theory as the mainstream approach:

 

From that article:

[i']Cosmologists sometimes state that the universe used to be the size of a grapefruit, but what they mean is that the part of the universe we can now see--our observable universe--used to be the size of a grapefruit.[/i]

 

*cough*... no that's wrong, at least, in terms of "mainstream physics" anyway...

 

why is the statement wrong "in terms of mainstream physics"?

it seems to be compatible with General Relativity, and the usual Friedmann model used in cosmology

[island]

why is the statement wrong "in terms of mainstream physics"?

it seems to be compatible with General Relativity' date=' and the usual Friedmann model used in cosmology[/quote']

 

Wow... this got interesting, fast... and you're right, Martin, I should have said that the boundary conditions of the open model aren't natural to GR because they're independent of the distribution of mass-energy.

 

The simpler solution lets the matter field determine the boundary conditions

 

"Einstein's theory...demands closure of the geometry in space ... as a boundary condition on the initial value equations if they are to yield a well-determined 4-geometry".

 

-Misner, Thorne, and Wheeler

 

Doesn't mean anybody listened...

[island]

Quick question...

 

Is' date=' or can General relativity agree with the idea that photons mediate the gravitational force? Yes or no?[/quote']

 

Not in a pure sense, I don't think, but yes, I think that there are modified theories that do just that, using GR, but I don't remember where I might have seen that.

[Martin]

Wow... this got interesting' date=' fast... and you're right, Martin, I should have said that the boundary conditions of the open model aren't natural to GR because they're independent of the distribution of mass-energy.

 

The simpler solution lets the matter field determine the boundary conditions

...[/quote']

 

Island, I am not sure you understood my question. The statement you quoted from the Sci Am article is not talking about boundary conditions.

 

Here, let me repeat the question so we can focus on it:

 

I guess that everyone has their own theoretical prejudice' date=' but they really shouldn't push unproven cutting-edge theory as the mainstream approach:

 

From that article:

[i']Cosmologists sometimes state that the universe used to be the size of a grapefruit, but what they mean is that the part of the universe we can now see--our observable universe--used to be the size of a grapefruit.[/i]

 

*cough*... no that's wrong, at least, in terms of "mainstream physics" anyway...

 

what I want to know is why you said "no that's wrong"? It seems very much in line with mainstream physics and with mainstream cosmology in particular.

 

The authors are saying that the observable universe used to be the size of a grapefruit (used to be smaller too but take a grapefruit as a convenient size) and I think pretty much any conventional working cosmologist (Michael Turner, Ned Wright, Sean Carroll, etc.) would agree. It is not controversial. But you say "*cough*, that's not mainstream physics". So naturally I am curious as to what your idea might be of what's right. And I am asking you to SPELL OUT what exactly you think is wrong and SAY EXACTLY WHY you think it is wrong.

 

I dont mean hints and suggestions but just straightforward say what is not mainstream conventional Gen Rel and conventional cosmology in what Lineweaver and Davis said here. This will give me an idea of how you think about these things, which I would like to know

[island]

So if island says go look at Ned Wright, and you like his style (as I do also) then study it! Wright teaches Cosmology at UCLA and has a world reputation and is reputable as hell and has responsibility for major projects.

 

Something else very important can be ascertained from Ned's site:

 

You can superpose Einstein's "negative energy waves", which would result in an opposing deconstructive potential when they aren't overlaping to produce a "self-energy".

 

Macroscopically, these look like zero, and there's a million dollar prize for that one...

 

See: Yang Mills, Mass Gap, Millennium prize

 

In this case, a "negative energy wave" is a gravitational wave that has a positive energy density but negative pressure, so that the wave density is smaller than the matter energy density, (but still positive), having a gravitational effect of positive energy density that's just outweighed by the gravitaional repulsion of negative vacuum pressure.

 

Superposition of these "negative energy waves" would result in a tangible non-zero minimum mass, because their combined density achieves quantized levels of positive pressure and matter density over a finite region of space, but would result in an opposing deconstructive potential, when they aren't overlaping to produce a "self-energy".

 

In Einstein's abandoned static universe, the vacuum has negative density when, P=-u=-rho*c^2.

 

P is proportional to -rho, but pressure is negative, and so energy density is positive.

 

The vacuum energy density is less than the matter energy density, but it is still positive, and it still has the gravitational attraction of positive energy density, but in this case, this gravitational effect is outweighed by the gravitational repulsion of the negative vacuum pressure. If you condense Einstein's vacuum energy over a finite region of space then it will achieve positive matter density over this region of space when the energy density equals that of the matter density.

 

The energy that's taken from this vacuum will, in-turn, cause negative pressure to increase, via the rarefaction of vacuum energy, so this near-flat spherical expanding universe does not run-away, because the increase in mass-energy is offset by the increase in negative pressure that results when you make particles from Einstein's negative energy vacuum.

 

All you need is a 1.2 MeV photon to make it a "permanent" thing, and it requires a greater volume of the vacuum each time that you make a particle, so the volume of the vacuum is now about a 120 orders of magnitude greater than one particle in every volume equal to the Compton wavelength of the particle cubed.

[island]

Island, I am not sure you understood my question. The statement you quoted from the Sci Am article is not talking about boundary conditions.

 

I know that, but they were assuming an infinite expanding universe, so I was coughing at the idea that the grapefruit was only a part of the whole big bang event, since you don't naturally arrive at this if the matter field sets the boundary conditions.

 

It only took me 14 edits to spit that out in a manner that finally seems to be right, so I must've REALLY screwed it up the first time...

 

"How I feel about it"

 

I think that Dirac's hole theory works just fine in Einstein's finite universe.

 

As with electric charge, the normal distribution of negative energy does not contribute to pair creation. Only departures from the normal distribution in a vacuum will isolate enough vacuum energy to produce virtual particle pairs. These pairs can be converted into real particles given enough energy, but they do not have negative pressure if they represent localized departures from the norm.

 

I think that unifies QM and General Relativity via the Dirac Equation... just like it was supposed to...

 

... and that fixes Dirac's Cosmological model

 

... which fixes his Large Numbers Hypothesis

 

... which necessarily clarifies and completes the Anthropic Principle, because that's where Robert Dicke got it from.

 

You asked...

[BlackHole]

I think that light (or any other form of electromagnetic radiation) may possess other properties we don't understand. It remains to be seen whether non-baryonic matter really exists. Could light be the mediator of gravity?

 

There may be a connection between photons and neutrinos but this is still speculative.

[Johnny5]

 

All you need is a 1.2 MeV photon to make it a "permanent" thing' date=' and it requires a greater volume of the vacuum each time that you make a particle, so the volume of the vacuum is now about a 120 orders of magnitude greater than one particle in every volume equal to the Compton wavelength of the particle cubed.[/quote']

 

Energy of a photon

 

[math] E = \hbar \omega = hf [/math]

 

h is plancks constant

hbar is plancks constant divided by 2 pi

 

[math] h = 6.6260755 \times 10^{-34} \frac{Kgm}{s^2} [/math]

 

This isn't NIST's value, its the one I memorized years ago, i don't know what it's at now.

 

At any rate, I am trying to compute the frequency such a photon would have.

 

You say...

 

1.2 Mev photon

1.2 million electron volt photon.

 

[math] 1.60217733 \times 10^{-19} \frac{\text{Joules}}{\text {electron volt}} [/math]

 

[math] (1.2 \times 10^6 eV)(1.6 \times 10^{-19}\frac{\text{Joules}}{\text {eV}} ) = 1.92 \times 10^{-13} \text{Joules} [/math]

 

Therefore:

 

[math]

 

1.92 \times 10^{-13} \text{Joules} = (6.6 \times 10^{-34} \frac{Kgm}{s^2} ) f [/math]

 

In the formula above, f denotes the 'frequency' of the photon.

 

So solving for f we have:

 

[math] f = \frac{1.92 \times 10^{-13} }{6.6 \times 10^{-34} } = 1.8 \times 10^{20} \ Hz[/math]

 

Where f has units of inverse seconds, which are called Hertz, named after German theoretical physicist 1857-Heinrich Rudolph Hertz-1894. He died young.

 

 

You are talking about "volume of the vacuum" are we talking a spherical volume here?

 

what's the formula for the Compton wavelength again, is this right?

 

 

[math] \lambda_{compton} = \frac{h}{2m_e c} [/math]

 

?

 

Thanks

 

Compton wavelength named after American Physicist 1892-Arthur Holly Compton-1962. He won the Nobel prize in physics in 1927, for his discovery that X-rays and scattered electrons appear at the same instant.

 

here is a reference to an article in 1933

 

IOP abstract referencing compton, 6 years after he won nobel prize

[Johnny5]

... because that's where Robert Dicke got it from.

 

You asked...

 

 

Who is Robert Dicke?

 

Regards

[island]

Who is Robert Dicke?

 

Regards

 

He was a very respected physicist, like Paul Dirac, and he was the first to discover an Anthropic coincidence within Diracs Large Numbers Hypothesis. Fred Hoyel was actually the first to call it that, but he may have had a hidden super-natural agenda.

 

 

 

In 1957, Robert Dicke noted that carbon based life can only exist in our universe when the Dirac's Large Numbers Hypothesis is true. Human existence is possible because the constants of the universe, and for planet Earth, lie almost exactly between the spectrum of potential, within certain highly restricted ranges. Dike's observation means that Dirac's Large Numbers Hypothesis is somehow true even though his cosmological model was flawed, but per the above "new" physics, Dirac's hypothesis is valid within the framework of Einstein's static model if the energy of the observed antiparticle exists in a negative energy state, (by way of negative vacuum pressure), until enough vacuum energy is condensed over an isolated region of space to achieve positive matter density.

 

 

 

This application exposes the causal mechanism for the Anthropic Principle, thereby giving the Strong Anthropic Principle real physical meaning, while removing the weakness that gets it labled as a tautology or a truism. It stands to good reason that repairing Dirac's cosmological model would also repair his large numbers hypothesis, thereby sheding new light on the anthropic principle, and Dirac, (who was known as 'the purist soul in physics', for his "self-honesty"), would expect no less from us, than we should take a hard look at what the math is telling us.

 

Dirac noted that the number of baryons, (protons plus neutrons), in the universe is equal to the square of the gravitational constant, as well as the square of the age of the universe, (both expressed as dimensionless numbers). From this, Rober Dicke realized that a even a slight change in either of these relationships life could not exist. Stars of the right type for sustaining life supportable planets only can occur during a certain range of ages for the universe. Similarly, stars of the right type only can form for a narrow range of values of the gravitational constant.

[island]

You are talking about "volume of the vacuum" are we talking a spherical volume here?

 

Yes!' date=' Einstein's static universe.

 

what's the formula for the Compton wavelength again, is this right?

 

Almost.

 

It's just, h/mc, where h is the planck constant and m is the mass of the particle. The compton wavelength for an electron is about 10^-12 meters.

 

Thanks

 

Great post!

 

Check out "antimatter" and particle pair creation...

 

I was also going to refer this article as it pertains to the anthropic principle... but I wrote it...

 

http://www.lns.cornell.edu/spr/2005-01/msg0066400.html

[Spyman]

Many physicists start to believe that cosmic inflation can explain the acceleration without the need for dark energy. Other believe it's an experimental error.

Thanks for all the links !

 

I will try to read through them when I get the time needed.

 

BTW Are You trying to convince me or Yourself ?

Just out of curiosity one might wonder since You have not presented a consitent view of Your own. You seem to favour any idea that is against an expanding space-time.

Or are You just polite and giving a lot of links for me to decide on my own ?

[Spyman]

No apologizing necessary Spyguy... I'm not ignoring you' date=' I've just been busy and I'm at a loss as to how I might explain it any better. Frankly, I don't necessarily dissagree with your point.

 

I was cheating by using new physics to *try* to explain it by adding a cosmological term to the field equations in a closed *expanding* universe, which is different than the commonly projected open expanding universe where Martin is coming from.[/quote']"Spyguy" ? Anyway I don't think it's so easy to "scare" You away...

 

Does this mean that I interpreted Your view correct this time or not ?

island view) Vacuum energy, vacuum have gravity which pushes bodies apart, the speed due to the push is not exceeding light but the creation of new vacuum causes that, important is that the push cancels out the normal grip of gravity between the bodies, energy don't have to be conserved since new energy is inserted from the vacuum.

[Spyman]

Maybe I already recommended you read the Lineweaver article and you already did and I forgot, but if you havent already, please do and then we have something to discuss. A little grit on the road for traction

Martin, we seem to go around in circles here...

I guess You have plenty of things going on and can't remember where the discussion was when You left off.

(You have recommended the article, I have read it, it didn't supply me with an answer.)

 

What I need is a straight forward answer, if I interpreted Your view correct or not ?

Martin view) Inertia, the metric is changing and nothing moves, energy is conserved by also streaching gravity together with space, the gravitational energy between the objects being streached apart is constant, so gravity is sort of "amplified" relative the metric with the same rate as expansion.

[Spyman]

Is, or can General relativity agree with the idea that photons mediate the gravitational force? Yes or no?

Johnny5, please keep Your discussion about "how photons mediate the gravitational force" in Your thread.

 

Found here: http://www.scienceforums.net/forums/showthread.php?t=10428

[YT2095]

Spyman,

 

4 posts in a Row is not a great way to use a Forum, please use your EDIT button to add further thoughts/Data where no one has posted after you.

 

Thanks

[Spyman]

Spyman' date='

 

4 posts in a Row is not a great way to use a Forum, please use your EDIT button to add further thoughts/Data where no one has posted after you.

 

Thanks [/quote']YT2095, You might be correct here, and I usually do that, but in this case I am answering different people and don't want to confuse the situation further by mixing all the answers in one huge post.

 

So, is it excused to do this in this particular situation or not ?

 

Also, sometimes when trying to make a huge post of that cind the system throws me out, (I have to logg in again), with the result of loss of all work and thoughts.

[YT2095]

Hmmm... I`m not sure why it "throws you out"?

 

although I have lost large posts in the past, I`ve learned to Cut my post before hitting Reply, that way (barring a Crash) I can re-paste it back later

as for the confusion, use the `

` function, seems to work great for the others (I`m not a fan of it myself though).

 

Sorry everyone for the Off Topicness, Continue