Inflationary Theory out of thin air?

[Chaos' lil bro Order]

Hey all, especially spacetiger, I have a question about inflationary theory for you.

Its my understanding that the Period of Inflation proposed to have occurred during the first second of the BigBang, was introduced to give a suitable answer to the Horizon Problem. The Horizon problem says that the thermal equillibrium we observe, as in the CMB, could not of been achieved in the early Universe since space expanded faster than C.

My question is: What evidence is there to support a Period of Inflation? Is the notion merely theoretical, or is there observable grounds for this theory?

Thanks.

 

[navneet1990]

if C is speed of light
then how can anything expand or grow or be faster than C
according to einteins theories

 

[Chaos' lil bro Order]

Relativity applies to matter and light, it says nothing about the expansion of the fabric of space itself. In fact, many regions of space are expanding at speeds in excess of C.

 

[navneet1990]

how do you explain that phenomena
any theories'? to support

 

[sdemjanenko]

i don't think they have any proof, they just believe that that would best explain what they are seeing. Otherwise it would completely blow open the previous theories

 

[navneet1990]

you can't just bend science to your will

 

[SpaceTiger]

There is much discussion of the evidence for inflationary theory here:

https://www.physicsforums.com/showthread.php?t=114527"

Very briefly, inflation predicts that the initial distribution of matter (prior to gravitational collapse) is described by a gaussian random field. There are several lines of evidence for this, including analysis of the CMB and large scale structure. Another prediction of inflation is that the spectral slope should be near, but not exactly equal to, unity. This has been confirmed by recent WMAP results.

However, both of these predictions are also consistent with Dr. Steinhardt's cyclic universe, so a real smoking gun for inflation would be the discovery of B mode polarization in the CMB. We hope to discover this with the Planck mission.

I can't give more detail right now, but just know that there is observational evidence for inflation that goes beyond the original motivations for it (as a solution to the horizon, flatness, and monopole problems).

 

[SpaceTiger]

how do you explain that phenomena
any theories'? to support

That objects can recede from one another at faster than the speed of light (due to the expansion of space) is a natural feature of Einstein's theory of gravitation and does not violate any tenets of relativity.

 

[franznietzsche]

if C is speed of light
then how can anything expand or grow or be faster than C
according to einteins theories

In flat, static spacetimes, c is a limiting relative velocity. In curved, time-varying geometries things are different.

 

[Chaos' lil bro Order]

There is much discussion of the evidence for inflationary theory here:

https://www.physicsforums.com/showthread.php?t=114527"

However, both of these predictions are also consistent with Dr. Steinhardt's cyclic universe, so a real smoking gun for inflation would be the discovery of B mode polarization in the CMB. We hope to discover this with the Planck mission.

).

Please explain to me what B mode polarization is and why it implies a cyclic universe?

BTW, I subscribe to the idea that the universe will collapse in the future and then undergo another bigbang.

 

[Chaos' lil bro Order]

you can't just bend science to your will

I'm pretty sure there have been astonomical observations of galaxies with recessional velocities in excess of C, and in fact in excess of 2C. Is this bending science, or empirical evidence?

 

[matt.o]

I'm pretty sure there have been astonomical observations of galaxies with recessional velocities in excess of C, and in fact in excess of 2C. Is this bending science, or empirical evidence?

It depends on which model you use to convert the redshift (observed) to a velocity. If you use plain old special relativity (SR) to derive a recessional velocity, you won't get a velocity exceeding c. Please note that cosmological redshift is not due to the SR redshift effect (ie. redshift due to velocity), hence using the SR method is wrong.

If you use general relativity (specifically, the $$\Lambda$$CDM model), you will derive a recessional velocity greater than c at redshifts > 1.6 since the redshift is due to the expansion of space, not some velocity through space.

So the term recessional velocity is a bit of a misnomer and astrophysicists generally use redshift instead, since this assumes no model.

PLease see http://arxiv.org/abs/astro-ph/0310808" for further information.

 

[Chaos' lil bro Order]

Which version of recessional velocity does the Friedmann Equation use then?

 

[matt.o]

The Friedmann Equations are derived from Einstein's Fields equations (General Relativity) under the assumption of isotropy and homogeneity. The first Freidmann equation relates the Hubble parameter to the density parameters and redshift and gives the time evolution of the Hubble parameter, H(z). This is used in determining the cosmological recession velocity in eqn 1 of the Davis and Lineweaver paper I linked above.

 

[hellfire]

Please explain to me what B mode polarization is and why it implies a cyclic universe?

Every theory that explains the origin of structures in quantum fluctuations of a scalar field predicts scalar and tensor modes that correspond to the E and B-mode of polarization respectively. In case of inflation the scalar field is the inflaton and is responsible for the accelerated expansion of space. In case of the cyclic model the dynamics in 3+1 space-time can be described also with an effective scalar field that produces the modes during the contraction phase before the big-bang.

 

[SpaceTiger]

Please explain to me what B mode polarization is and why it implies a cyclic universe?

I hope I didn't say that anywhere in the WMAP thread. It's the opposite actually, the detection of B mode polarization in the CMB would be evidence for inflation and against the cyclic universe. Most theories of inflation produce gravitational radiation, which induces tensor modes, which in turn induce B-mode polarization in the CMB light. The cyclic universe, on the other hand, generically produces no gravitational radiation, so no B-mode polarization in the CMB.

An alternative to (or supplement to) looking for B-mode polarization in the CMB is to just look for the gravitational radiation directly, but this will likely be much more difficult. We've yet to detect any gravitational waves directly.

 

[Mike2]

The Friedmann Equations are derived from Einstein's Fields equations (General Relativity) under the assumption of isotropy and homogeneity. The first Freidmann equation relates the Hubble parameter to the density parameters and redshift and gives the time evolution of the Hubble parameter, H(z). This is used in determining the cosmological recession velocity in eqn 1 of the Davis and Lineweaver paper I linked above.

This is not consistent with:

Relativity applies to matter and light, it says nothing about the expansion of the fabric of space itself. In fact, many regions of space are expanding at speeds in excess of C.

Is the expansion factor put in by hand or derived?

 

[Mike2]

Does anyone know when the false vacuum of the Higgs mechanism fell to its present low compared to the acceleration/deceleration of the expansion rate? Did this fall to the present stable energy level take place about the time that the universe started to decelerate in it expansion?

I'm considering a theory where the energy in the Higgs field, at its greater than present vacuum energy level, is what forced the universe to expand exponentially. Then at some point there was no longer enough vacuum energy density to keep the expansion accelerating. But the momentum of expansion put a force on the vacuum energy to cause it to fall to a new level, creating particles, etc, in the process. That would be supported by the fact (if true) that massive particles first appeared at about the same time the universe started to decelerate, and not before. Is this indeed the case? Thanks.

If so, then what does that mean for the present acceleration of expansion? Are we looking at a new phase of particle creation when the present vacuum energy can no longer support expansion, but the momentum of expansion creates a force instead on the present vacuum energy that causes it to fall again to a new energy level? I wonder what the implications of that would be?

 

[matt.o]

This is not consistent with:

That is because Chaos was talking about Special Relativity.

Is the expansion factor put in by hand or derived?

The expansion factor ($$\dot{R}(t)$$) is given by eqn 26 in the Davis and Lineweaver paper. I just put in values for redshift and the cosmological parameters for the $$\Lambda CDM$$ model (ie., $$\Omega_{\Lambda}=0.7$$ and $$\Omega_{m}=0.3$$).

What I was trying to get across is that we don't measure recessional velocities, we measure redshifts and convert them using a model dependant method.

 

[hellfire]

I hope I didn't say that anywhere in the WMAP thread. It's the opposite actually, the detection of B mode polarization in the CMB would be evidence for inflation and against the cyclic universe. Most theories of inflation produce gravitational radiation, which induces tensor modes, which in turn induce B-mode polarization in the CMB light. The cyclic universe, on the other hand, generically produces no gravitational radiation, so no B-mode polarization in the CMB.

It is difficult to understand that while it produces a similar spectrum of density perturbations, it difers so much in the tensor perturbations... ?

 

[SpaceTiger]

It is difficult to understand that while it produces a similar spectrum of density perturbations, it difers so much in the tensor perturbations... ?

What I said is incorrect, actually. The cyclic universe does produce gravitational radiation, but the spectrum is much bluer. This means that at long wavelengths (like those we can measure in the CMB), the intensity of gravitational radiation is negligibly small.

I won't attempt to explain the origin of the difference, but Dr. Steinhardt gives a pedagogical explanation on page 9 of his http://www.physics.princeton.edu/~steinh/dm2004.pdf" .

 

[Chaos' lil bro Order]

What I said is incorrect, actually. The cyclic universe does produce gravitational radiation, but the spectrum is much bluer. This means that at long wavelengths (like those we can measure in the CMB), the intensity of gravitational radiation is negligibly small.

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Interesting ST. Does it make sense to look for gravitational radiation at high EM energies than, since the signal would be stronger and thus easier to observe?

Does LISA have a preferred wavelength region where she will be looking for graviatational radiation?

 

[FunkyDwarf]

my understanding of this (from my uni textbook) is that one theory to explain it (i know you asked for evidence but its an interesting point of information anyway) is the decoupling theory.

In a nutshell it talks about the fact that at the start all the forces were more or less one force, which then split off to the strong and the electroweak forces which later split into the four we know today. This split , apparently, creating what i liken to, though I am not sure it is, a massive change in entropy in the universe forcing it to an unstable high energy state. This was then corrected by using this excess energy to expand space rapidly.

But yeh as for evidence all i know is the horizon problem. I know its bascially evidence for itself and thus cyclical but i think it works well.

 

[Chronos]

There are layers of model dependent interpretations of the raw WMAP data, and more than one viable explanation for modal anomalies observed. The LCDM model remains a front runner [is more predictive than the rest of the pack] but still suffers from anomalies - just less severely than the competing ponies.

 

[Chronos]

That was a provocative argument FD, and interesting. I see a break in the logical constructs you have proposed on many levels. You appear to impose background dependence, yet shy away from specific predictions. I find that alarming and treading the line between science and . . . metaphysics. Those are my boundary conditions, not yours, and I set the line arbitrarily. Your ideas are interesting, but not sufficiently grounded to suit my taste - not that it matters. I merely think many mainstreamers would sympathize with my position. But I encourage you to take a poll. I could very well be wrong.

I perceive the universe as a very well ordered, yet chaotic set of events driven by the laws of thermodynamics . . . it gets even weirder with age. I see it as becoming more predictable as a function of redshift . . . i.e., more uniform at earlier ages after the putative 'Big Bang' than in the present epoch. That's my position in a nutshell. I rarely see any arguments that more than briefly object to these fairly simple premises on less than cursory evidence. That bothers me.

Let's talk about the infinitely old universe thing in brief. Where are the burnt out galaxies that should be 'infinitely' abundant? This proposition is, IMO, outlandishly wrong and illogical. It's an 'excuse me' theory that hinges on the 'stake' to symbolize the purity of their cause.

I have no clue why the universe is finite in age. Nor do I have any clue why it is bounded. The evidence says it is. That is my only excuse.

 

[Mike2]

In a nutshell it talks about the fact that at the start all the forces were more or less one force, which then split off to the strong and the electroweak forces which later split into the four we know today. This split , apparently, creating what i liken to, though I am not sure it is, a massive change in entropy in the universe forcing it to an unstable high energy state. This was then corrected by using this excess energy to expand space rapidly.

If the vacuum energy during inflation had a higher energy level, then this argues for a larger value of h-bar than today - on the average zero point energy was allowed to be greater for the same period of time. That means that there was more uncertainty in measurements than now. But since there was only one force, there were fewer degress of fredom at that time. Then inflation stopped. The vacuum energy fell to its present value which means that h-bar became smaller. This would have a tendency to decrease uncertainty in the universe. But at the same time, there came more degrees of freedom as more forces became available to complicate the configuration of particles. I have to wonder how h-bar and the number of forces play into the entropy of that transition.

 

[FunkyDwarf]

Its a good point, like i said I am simply reiterating what I've read. As i see it though they weren't really one force as such, rather they were grouped together because under the conditions of the time they all acted the same. As these conditions changed so the forces that decoupled exibited different behaviours and effects, thus affecting the world around them in a way that affected the overall entropy.

 

[Chronos]

FD, if you are saying entropy evolves, I agree. If you are hedging your bets, that too is understanable. There are fewer flawed observations in cosmology than flawed theories IMO. I also question if a 'pure' TOE is a realistic goal.

 

[Chaos' lil bro Order]

FD, if you are saying entropy evolves, I agree. If you are hedging your bets, that too is understanable. There are fewer flawed observations in cosmology than flawed theories IMO. I also question if a 'pure' TOE is a realistic goal.

TOE must be the ultimate goal. Realistic or not, its the accumulation of all goals IMO. If we find a TOE for our Universe, we may then be searching for a Multiverse TOE. Each TOE we find, will open another TOE up to us. TOE upon TOE upon TOE. That's a lot of toes, considering that all this little piggy wanted in the first place was some roast beef.

:)

 

[FunkyDwarf]

i had a feeling that was coming :P

 

[Mike2]

Its a good point, like i said I am simply reiterating what I've read. As i see it though they weren't really one force as such, rather they were grouped together because under the conditions of the time they all acted the same. As these conditions changed so the forces that decoupled exibited different behaviours and effects, thus affecting the world around them in a way that affected the overall entropy.

As I understand it, the other forces diverged from the one force through some mechanism of symmetry breaking. And I've suggested that h-bar was larger during inflation when the forces were one. So I have to further wonder if the required symmetry breaking process could be accomplished by a reduction of h-bar. Since h-bar has the units of an action, a larger h-bar argues for more invariance in the action integral. If the minimum possible action is larger, then changes in the action integral with respect to variables within it will still be within that minimal amount of h-bar and thus not noticed. So if the minimal possibe action becomes smaller, then invariances will have a more noticeable change in the action integral, and previous symmetries may dissappear. Any thought on this anyone? Thanks.

 

[Chronos]

The problem I see mike2 is a scaling h parameter is irrelevant prior to the emergence of spacetime - assuming spacetime is emergent. Albeit might be a factor in a background dependent model. BTW, I have a link you might find interesting:

Probability Theories with Dynamic Causal Structure: A New Framework for Quantum Gravity
http://arxiv.org/abs/gr-qc/0509120

 

[Mike2]

The problem I see mike2 is a scaling h parameter is irrelevant prior to the emergence of spacetime - assuming spacetime is emergent. Albeit might be a factor in a background dependent model. BTW, I have a link you might find interesting:

Probability Theories with Dynamic Causal Structure: A New Framework for Quantum Gravity
http://arxiv.org/abs/gr-qc/0509120

What do you suppose spacetime emerges from?

From what I can gather, h-bar shows that space and time are related in a spinfoam type QFT to matter and energy. The delta-energy*delta-time>h-bar indicates time (a spacetime property) in relation to energy (a particle property), whereas the delta-momentum*delta-position>h-bar indicates space (a spacetime property) in relation to mometum (a particle property). So it seems spacetime is inexerably connected to vacuum energy (virtual particles).

If h-bar were zero it seems spacetime would be exactly correlated with energy-momentum. But if h-bar were larger, then expansion (of spacetime) would not be well correlated with vacuum energy (virtual particle properties).

 

[Chronos]

A universe from nothing would be my guess.