Inflationary Theory out of thin air?

1. Sep 4, 2006

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 occured 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.

2. Sep 5, 2006

navneet1990

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

3. Sep 5, 2006

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.

4. Sep 5, 2006

navneet1990

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

5. Sep 5, 2006

sdemjanenko

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

6. Sep 5, 2006

navneet1990

you cant just bend science to your will

7. Sep 5, 2006

SpaceTiger

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

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).

Last edited by a moderator: Apr 22, 2017
8. Sep 5, 2006

SpaceTiger

Staff Emeritus
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.

9. Sep 5, 2006

franznietzsche

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

10. Sep 5, 2006

Chaos' lil bro Order

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.

Last edited by a moderator: Apr 22, 2017
11. Sep 5, 2006

Chaos' lil bro Order

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?

12. Sep 5, 2006

matt.o

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" [Broken] for further information.

Last edited by a moderator: May 2, 2017
13. Sep 6, 2006

Chaos' lil bro Order

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

14. Sep 6, 2006

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.

15. Sep 6, 2006

hellfire

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.

Last edited: Sep 6, 2006
16. Sep 6, 2006

SpaceTiger

Staff Emeritus
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.

17. Sep 6, 2006

Mike2

This is not consistent with:

Is the expansion factor put in by hand or derived?

Last edited: Sep 6, 2006
18. Sep 6, 2006

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?

Last edited: Sep 6, 2006
19. Sep 6, 2006

matt.o

That is because Chaos was talking about Special Relativity.
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.

Last edited: Sep 6, 2006
20. Sep 7, 2006

hellfire

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

21. Sep 7, 2006

SpaceTiger

Staff Emeritus
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" [Broken].

Last edited by a moderator: May 2, 2017
22. Sep 7, 2006

Chaos' lil bro Order

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?

23. Sep 18, 2006

FunkyDwarf

my understanding of this (from my uni text book) 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 im 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.

24. Sep 19, 2006

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.

25. Sep 21, 2006

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.

Last edited: Sep 21, 2006