Good question! As I understand, the small scales of cosmological effects within our cosmological neighborhood prevents meaningful evaluation. That is to say that the reacceleration of universal spacetime expansion has (at least initially) been inferred from discrepancies between distance estimates derived from type Ia supernovae luminosities and distance estimates derived from their host galaxies' comological redshifts applied to cosmological models (the discrepancies were resolved by including a cosmological constant parameter to the cosmological models).

Since the cosmological redshift (imparted by the accumulated effects of spacetime expansion) of light from objects in our own cosmological neighborhood is very small, the discrepancy inferring universal acceleration (and the influence of a cosmological constant) does not appear in data related to our cosmological neighborhood.

I do find though, that the initial Reiss, et al. analysis http://arxiv.org/abs/astro-ph/9805201 stated in section 6 - "Conclusions" that:

"2. The distances to the spectroscopic sample of SNe Ia measured by two methods are consistent with a currently accelerating expansion (q0¹0) at confidence levels from 99.5% (2.8 p) to more than 99.9% (3.9 p) for q04()M/2) [)" using the prior that )Mº0."

[see source text for correct formatting]

However, the preceding section concludes:

"Our detection of a cosmological constant is limited not by statistical errors but by systematic ones. Further intensive study of SNe Ia at low (z\0.1), intermediate (0.1¹z¹0.3), and high (z[0.3) redshifts is needed to uncover and quantify lingering systematic uncertainties in this striking result."

I interpret this initial finding to be consistent with the question you raise. I'm not familiar enough with subsequent research to determine whether these systematic proximity uncertainties have ever been satisfactorily resolved, or simply overlooked...

2011 Physics Nobel Prize was won by Riess, Perlmutter and Schimidt for their studies on the accelerated expansion of the Universe. This is based on their studies of Type Ia

supernovae (binary system where one of the star is a white dwarf accreting mass from its neighbour. Once white dwarf mass reach Chandrasekhar limit - 1.44 solar masses - it explode). They are believed to be quite good standard candles by which you can measure their host galaxy distance. Put in a simple way, you can draw an Hubble diagram for these objects where you have distance modulus (apparent minus absolute magnitude) versus red-shift from which it results that the rate of expansion of the universe at that time was smaller then the one measured from nearby objects (e.g. now). Therefore the Universe is increasing its rate of expansion hence it is accelerating.

Davide,

The use of type Ia supernovae as standard candles presumed that they are produced only by a white dwarf accreting mass from a companion (red giant) star until it reaches 1.38 solar masses - producing a supernova of consistent peak emission source luminosity.

However, in the past few years an alternative model for type Ia SNe progenitors have gained supporting observational evidence. In this case, two colliding or merging white dwarf stars actually produce type Ia supernovae of varying mass (usually > Chandrasekhar limit). As a result, peak emission source luminosity also varies - rendering these events invalid for use as standard candles in estimating distance based on their apparent luminosity. Please see http://www.nasa.gov/home/hqnews/2012/mar/HQ_12-086_Swift_TypeIa_Origins.html. Also see http://www.news.pitt.edu/supernovae, http://arxiv.org/abs/1201.0994 and http://arxiv.org/abs/astro-ph/0311484, for example.

Paul Sherard's answer is the usual one, leading to the 2011 Nobel prize in physics. However, there is an alternative explanation to the systematic dimming of the SN1A events; that is, that these may be systematic dimming errors due to primordial dark matter planets that surround all stars because all stars are formed by merging of dark matter planets (Gibson 1996, confirmed by Schild 1996). Please see journalofcosmology.com for several papers showing the theory and observational evidence. Both the accelerating expansion of the universe and the anti-gravitational dark energy explanation are falsified by the observations. This is the first ever Nobel Prize in physics to be falsified. Dark energy is equivalent to the "nonobtainium" material mined in the movie Avitar. There is no such material.

See recent paper at RG by Julio A. Gonzalo & Manuel Alfonseca pointing out exctly what Paul Sherard is saying here.

We hope future work on the same subject will show that a good explanation to the almost imperceptible upward curveture in the Distance vs. Resshift Hubble plot taken currently as accelerated expansion can be mimiced within a properly reformulated open Friedman- Lemaitre model with Lambda equal zero at high redshifts.

This is actually a contentious issue with much revisionist history going on. I am sure someone(s) will eventually react quite negatively to what I post below in historical order.

The signal of the acceleration in the original 1998 paper by Riess etal (and the other groups) is weak at best. The strongest signal is actually clearly showing that

Omega Matter can not be one. This then leads to the following indirect argument which persists to this day:

Inflation is correct (assumption)

Under the assumption space is flat

Omega_matter is no longer high enough to make space flat therefore spaces is flat because Omega + Lambda = 1.

Boomerang Balloon experiment of 1999 provides first reasonable evidence from the MWB that space is flat - subsequently verified with higher S/N by WMAP and with even higher S/N by Planck.

Revisionist history (a favorite pastime of many scientists) will now claim that SN provided "independent" evidence of non-zero Lambda. I don't believe that is the case (but what I believe is irrelevant). The SN data were consisted with inflation produced flat space and did show that Omega_matter was not 1; that data did not

independently measure Lambda, despite the Nobel Prize.

This will become an interesting exercise in the history of science much like the recently revived historical debate about who really discovered the expanding Universe (Slipher vs Hubble vs Lemaitre vs Friedmann).

And finally, I and others still believe that the full systematics of SN Ia properties are not fully known to the required level for using them as probes of Precision

Cosmology.

G. Bothun,

IMO, that a positive cosmological constant (and a negative deceleration parameter) were used (by the researchers that originally identified the acceleration of universal expansion in the late 1990's) to fit then standard cosmological models' distance estimates derived from host galaxy redshift to distance estimates derived from type Ia SNe luminosities was more a matter of parametric fine-tuning than a discovery of evidence for any accelerating force.

IMO, negative pressure is presumed to be produced by the cosmological constant parameter - but that has not physically been established as the cause for the apparent acceleration of expansion. The simplifying underlying assumption of Friedman and cosmology in general is that the universe is homogeneous. The temporal development of 'large scale structure' (at smaller than universal scales) conflicts with that assumption and may affect temporally developing universal dynamics - especially the acceleration of expansion. See http://arxiv.org/abs/1109.2314 and especially http://arxiv.org/abs/1311.3787. Temporal development of included large voided regions seems likely to require that the rate of universal expansion increase, as the density of voided regions can be much lower than the universal average density.

Yes

Things are fine tuned under the assumption that FRW is correct metric and yes

we have not physically established the value for Lamba or its physical nature.

We have established that a) the Universe is flat and b) there is not enough matter density to make it so.

@ G. Bothun,

Einstein said that introducing the cosmological constant

is his greatest mistake. But after the analysis of current

data from Planck and WMAP is done, is the value of lambda

consistent with zero ?

Biswajoy,

Einstein included the cosmological constant to prevent the then observed universe (actually the gravitationally bound Milky Way galaxy) from eventually collapsing as a result of gravitation.

As I understand, the value of Lambda is being evaluated as the sole cause of the reacceleration of spacetime expansion in a continuously homogeneous universe. There could be a cause for the acceleration of expansion that is not related to any negative pressure from vacuum energy density - especially in a universe that is becoming increasingly inhomogeneous at increasingly larger scales - contributing to the universal expansion of spacetime..

How does vacuum energy density remain constant in an expanding dimensional spacetime?

[I have attached a generic plot of the expansion of the universe in time. The Omega-m = 0.3 and Omega-L = 0.7 curve is the accepted LCDM fit.] Many of the responses to my question have indicated there may be some problems with the LCDM curve fit. I would like to reiterate what my question is addressing. The plot shows clearly what I am trying to point out. The observed expansion for the past 3-4 billion years can be fit nearly perfectly with a straight line. The “acceleration” shown by LCDM curve fit is merely an extrapolation. We would need to wait another 2-3 billion years into the future before we could observe a non-linear expansion according to the LCDM fit. Thus, we are not observing any acceleration “now” nor will we for a long time to come. The acceleration occurring “now” as predicted by the LCDM curve fit is just that, a prediction. It is not based on empirical evidence of the recent expansion. Viewing the expansion over the past 2-3 billion years is 10%-20% the age of the universe. This time range is not negligible and therefore the significance of linear fit over that range cannot be simply ignored. The LCDM fit “ignores” this linear fit issue by claiming this is simply an inflection in the overall expansion curve. This, of course, is the well known coincidence problem. So, is the expansion curve truly linear in the recent history of the universe or are we simple witnessing a temporary inflection in an accelerating universe? In my mind that is an open question.

Your plot is not exactly identical to the plot in Physics Today reporting the finding of the 2012 Nobel prize winners. Their plot, more indirect, gives magnitude vs redshift.

But z (redshift) is only approximately proportional to velocity , and only for relatively low velocities ( v/c1) should show up in an upwards deviation from pure linearity.

The data deserving the Nobel Prize go up to z slightly above one.

Since 1998, apparently no further data for substantially higher z confirming the upwards trend have been published.

Perlmutter himself , in his original report, pointed out that possible corrections to the magnitudes of relatively distant galaxies for dimming due to dust and higher matter matter density at early times might be in order.

As I pointed out in my previous comment, Manuel Alfonseca and myself are examining these corrections ( relevant previous 2013 work is available at our Research Gate pages) as well as their relavance to the accelerated expansion. In our follow up work we are examining whether or not the Lambda CDM model is validated by the 2013 Plack´s satellite data as currently affirmed .

In any case we are concluding that a non zero Lambda is not absolutely necessary at all to justify an apparent accelerated expansion.

Since we derive the rate of spacetime expansion primarily from cosmological redshift, the magnitude of cosmological redshift imparted to light must significantly exceed the spectral shift imparted by peculiar velocities resulting from local gravitational interactions before any effects of expansion can be reliably identified.

In other words, cosmological redshift resulting from spacetime expansion cannot be reliably isolated from varying local gravitationally induced relative motions until it is the dominant contributor to the redshift of observed light. As a result, no 'contemporary' rate of expansion can be determined.

To the extent that the expansion rate of 'large scale structure', especially voids - whose 'local' mass-energy density is far less than any indeterminable contemporaneous universal average - increasingly contributes to the universal average rate of spacetime expansion, the average expansion rate may increase without any separate force effect that specifically increases the rate of spacetime expansion. In this case the acceleration of universal expansion may be a product solely of the diminished mass-energy density of growing void structures.

suppose I am considering z=10

Then

z=(delta lambda)/lambda =10 ----> Eq.(1)

You are saying that this delta lambda is

due to peculiar velocity and not due to the

cosmic expansion; is that right ? Also please

let me know whether Eq. (1) is the right relation

to use in this case.

Biswajoy,

If you're addressing my preceding comment, I'm afraid I cannot asses in the context of math or physics, but I suspect the equation you suggest is not useful. The term 'peculiar velocity' is most often used to refer to local gravitational interactions. That's not what I'm describing.

I'm suggesting that the cosmic web can be generalized as a reticulated foam structure, comprised of porous bubbles whose cell walls have collapsed into the filamentary edge material. Unlike a bath sponge, however, the edge structures aren't stable. While the spacetime of voids is expanding, the material within filaments is locally contracting.

I'm suggesting that the average rate of spacetime expansion in a universe that is increasingly comprised of growing voids whose mass-energy density is exceedingly low - must increase over time.

Some of the specific effects of the cosmological condition I'm attempting to describe are at least partially addressed in http://arxiv.org/abs/1209.3142 - its abstract states:

"More than half of the volume of our Universe is occupied by cosmic voids. The lensing magnification effect from those under-dense regions is generally thought to give a small dimming contribution: objects on the far side of a void are supposed to be observed as slightly smaller than if the void were not there, which together with conservation of surface brightness implies net reduction in photons received. This is predicted by the usual weak lensing integral of the density contrast along the line of sight. We show that this standard effect is swamped at low redshifts by a relativistic Doppler term that is typically neglected. Contrary to the usual expectation, objects on the far side of a void are brighter than they would be otherwise. Thus the local dynamics of matter in and near the void is crucial and is only captured by the full relativistic lensing convergence. There are also significant nonlinear corrections to the relativistic linear theory, which we show actually under-predicts the effect. We use exact solutions to estimate that these can be more than 20% for deep voids. This remains an important source of systematic errors for weak lensing density reconstruction in galaxy surveys and for supernovae observations, and may be the cause of the reported extra scatter of field supernovae located on the edge of voids compared to those in clusters."

Since large scale structure did not exist in the early universe, It seems necessary that it developed over time. This implies that the size of voids has also increased in time - as a result, the effects described above must have also evolved...

Sorry I can't be more helpful!

I see your points. Thanks a lot. I know what is gravitational lensing

but let me know what is weak lensing. Also please let me know

how much error can creep in when we study supernova explosions

at high red shifts caused by gravitational lensing.

Biswajoy,

The term gravitational lensing is, I think, most often used to refer to strong lensing, in which a very compact, dense object profoundly curves spacetime around it. Weak lensing is a subtler effect, generally produced by a somewhat disperse aggregation of masses, such as a galaxy cluster (and is used to infer the presence of dark matter in galaxy clusters). In weak lensing minute, directional optical distortions to perhaps thousands of background galaxies must be statistically identified. Galaxies appear to be elongated along an axis pointing to the center of the lensing structure.

In weak lensing produced by a void, I'd expect tiny distortions to background objects dispersed over a very broad expanse of spacetime. See http://en.wikipedia.org/wiki/Gravitational_lens and http://en.wikipedia.org/wiki/Gravitational_lensing_formalism for more information and references.

As for the potential for error for high-z SNe - I'd have to defer to the ref. in the preceding comment, but from what I read I think its being suggested that objects on the far-side of nearby voids would appear brighter than expected as a result of the void - whether those objects are near the void or far away. Conversely, acceleration of expansion was inferred by SNe that appeared dimmer than predicted by cosmological models without any acceleration compensation factors (cosmological constant and negative deceleration parameters). As a result, I would not expect this void lensing effect to account for the inferred acceleration.

Do you know what is the ratio of volume of structures to the

volume of voids ? Thanks in advance.

Biswajoy,

No, I don't Relying on the quote in the previous comment, "More than half of the volume of our Universe is occupied by cosmic voids..." (I think I saw 60% mentioned elsewhere, but I think these are all value judgments) would imply that less than half of the universe's volume exhibits greater mass-energy density than voids. Filaments are thought to be comprised of dark matter and galaxies: it seems that even their density would be both locally and, IMO most importantly, temporally variable - as would the percentage of spacetime occupied by voids...

James:

Good point. Then when a photon signal is traveling to earth after being

originated from a distant supernova burst, on an average, about

half of the time it is traveling through voids and rest through structures.

In voids there is nothing to bend its path, but when it passes through

structures it will have some bending of directions, do you agree ?

Then that should, in principle, introduce a systematic error in

distance estimates. Then a valid question is that will it affect

presently accepted notion of an accelerated expansion.

Biswajoy,

In that previous reference http://arxiv.org/abs/1209.3142 - it's asserted that

"Contrary to the usual expectation, objects on the far side of a void are brighter than they would be otherwise."

Moreover, in material filaments, light supposedly passing through the only the disperse dark matter would not be affected by material diffraction, only slightly by weak gravitational lensing. Both voids and filaments may introduce disparate systematic error effects - that likely vary as a function of distance and emission age - affecting structural characteristics of traversed spacetime...

I agree - it seems that both should be considered, but I can't evaluate whether those effects, if they can be adequately determined, might account for the (at ~5 Glya, ~10%) discrepancy between distance estimations derived from type Ia SNe luminosity and those derived from cosmological models (without compensatory positive cosmological constant and negative deceleration parameters).

Strictly from lensing effects, it seems that the proposed void's brightening effect alone could not account for the finding the type Ia SNe were ~10% dimmer than expected...

IMO it must primarily be considered that - aside from any lensing effects on observed light - the exceedingly low mass density of voids should produce local expansion rates that actually far exceed the universal average. To the extent that voids represent an increasing portion of universal spacetime, their elevated rates of regional spacetime expansion should contribute to the actual acceleration of universal expansion!

James:

I am reading your last post repeatedly. Because I am quite a novice

in astrophysics; allow me to ask a few questions.

type 1a SNe were 10% dimmer than expected. How do we estimate

expected brightness and then find them 10% dimmer ? In cosmological

models is it not required to input brightness of heavenly bodies as

parameters ? I guess that is the "philosophy". From big-bang model

we theoretically estimate luminosities of distant objects such as

type 1a SNe and then compare predictions with observed numbers.

Biswajoy,

I was recalling what I'd read some time ago in http://arxiv.org/abs/astro-ph/9805201 - one of the two 1998 studies of type Ia SNe that identified the original evidence supporting an accelerating universe. The actual quote from the abstract is :

"The distances of the high-redshift SNe Ia are, on average, 10% to 15% farther than expected in a low mass density (Omega_M = 0.2) Universe without a cosmological constant."

Section 5 "Discussion" on page 18 of the preprint states:

"High-redshift SNe Ia are observed to be dimmer than expected in an empty Universe (i.e., Omega_M = 0) with no cosmological constant."

The Omega_M (mass density) and cosmological constant refer to cosmological model parameters. The researchers used then standard (pre-Lambda-CDM) cosmological models to estimate the distance to the SNe host galaxies, based primarily on redshift.

Those estimated distances/magnitude (brightness) were compared to those derived from the peak period luminosity of the type Ia SNe used as standard candles (presuming that the supernova explosions always occurred when an accreting white dwarf star reached 1.38 solar masses) - their peak-period emission luminosity was expected to always be consistent. There have recently been some exceptions to the expected consistency, but it's thought that they will not affect the original results...

That the almost direct derivation of distance from luminosity did not match the cosmological model's predictions indicated that there was some invalid assumption in the model - the researchers were able to fit the models' predictions to observational estimated by changing the cosmological constant parameter from 0 (no 'negative pressure' effect) to a positive value (indicating some unknown source of negative pressure) and changing the deceleration parameter (indicating expansion entropy) from a positive value to a negative one.

I hope that helps - please keep in mind that I have no education or background in physics or math - so I have no formal qualifications. i'm a retired information systems analyst. I found the paper referenced above to be a very difficult read, but very informative - it's extremely well done - I recommend it!

Best wishes!

Let us have a look at the picture uploaded by Paul Sherard.

Each graph in this graph correspond to different universes, where

each of them are distinctly different from each other. Each of

them will have a distinctly different prediction for Luminosity

of type 1a SNe. We should examine which one is agreeing with

experimental data. As you have said in third para line 3 of your

previous comment. I agree with you in this regard rather than

searching for a cosmological model which is predicting 10% more

luminosity. In general if there are n parameters in a model and

n-m observational inputs then m free parameters always remain

to be adjusted. Similarly if there are n+m observational inputs

then model is over constrained. Nothing can be adjusted

in that case, that model can be accepted only if it is the right

one.

Biswajoy,

The charts represent a homogeneous universe in which large scale structure does not exist. What is the significance of average galaxy distance as a as a measure of mass density in a universe consisting of condensed material filaments and enormous voids? This is not a consensus opinion, of course...

Voids expand faster than other regions (Sahni & Coles '95) must have

made assumptions regarding absence of dark matter inside voids.

If dark matter is there within voids then they cannot expand faster.

Of course perturbation theory assumes deviations from isotropy

and homogeneity. But this should be a first order effect in perturbation

parameter.

Biswajoy,

Good point. Re. dark matter - it is inferred from gravitational effects (which often includes lensing) that seem to exceed those thought to be produced by identified luminous matter. As I understand, the inference of DM is critical to the process of identifying the fliamentary structures in simulation models...

As we see structures of luminous matter, such as galaxies and

galaxy clusters. Dark matter also should have some form of

structures. We do not know what are those structures. But always

there is a gravitational interaction between dark matter and

luminous matter. Therefore, will dark matter structures be gravitationally

tied to luminous structures, and voids will remain simple voids

without neither luminous nor dark matter ? This is perhaps a

natural case. Thinking otherwise, that voids will contain

large amount of dark matter only (without luminous matter)

seems unnatural due to the presence of gravity. I guess

thus voids will indeed expand faster making bubble like

things.

The expansion rate is not increasing.  The idea of dark energy is incorrect and unnecessary.

Yes, there are many cosmologists who question the fact that a cosmological constant (Lambda) is non-zero. But it is another thing to prove it otherwise. The solution is to prove that the LCDM model is wrong. Better yet, devise a theory that explains the perceived "acceleration" is an artifact of a misinterpretation of space-time at cosmological scales, namely the geometry of space-time.

  The perceived flatness problem plays a role here. If the spacial geometry of the universe is truly flat (k=0) then we have a problem. There could not have had been a beginning. This is usually not how that problem is stated concerning a truly flat universe.  So inflation theory was invented to say that, well that “beginning” was a monstrous “e-folding” where the universe expanded “faster than the speed of light” and then apparently shut off so that all appears flat. The same thing will eventually happen again if Lambda is positive. In fact an exponential expansion will eventually occur even if a positive Lambda is infinitesimally small. The entire history of the universe leads to the same behavior, namely exponential expansion, no matter what the value is of a positive Lambda.

   It is the perceived geometry of space, namely flat, that is causing us to continually to put “epicycle” upon epicycle (fine tuning) to fit observation. Perhaps it will take another Copernicus to discover the true nature of the geometry of space-time and finally put to rest arguments that have continued since Friedmann and Lemaître proposed the idea of an expanding universe nearly 100 years ago.

Observations of the very distant type Ia supernovae belonging to the remote Universe show that they are fainter than expected as compared to the nearby type Ia supernovae belonging to the local Universe. The brightness of the distant type Ia supernovae being fainter than expected suggests that the distances to them are larger than expected. This observation indicates that the expansion of Universe is accelerating. The Hubble diagram that is linear for the local structures deviates from linearity for the remote structures. The deviation of the Hubble diagram from linearity is an indication of acceleration.

However, according to my paper, distances to the remote structures being larger than expected, or the deviation of the Hubble diagram from linearity at large distances does not indicate an acceleration. I have found that the expansion pattern of large-scale structures into the Universe as depicted by the Hubble diagram is similar to the pattern of gas molecules undergoing free expansion into the vacuum – the Hubble diagram or the linear velocity-distance relation is a natural feature of gas molecules undergoing free expansion into the vacuum. The free expansion of gas molecules into the vacuum not only explains the linear velocity-distance relation, it also explains the deviation of Hubble diagram from linearity at large-distances without any acceleration.

“Molecules can explain the expansion of the Universe”

https://www.researchgate.net/publication/331983227

Direct evidence for an accelerating Universe came from observations of type Ia supernovae by the High-Z Supernova Search Team (Riess et al. 1998) and by the Supernova Cosmology Project team (Perlmutter et al. 1999).

Their research showed that remote supernovae are 10% to 25% dimmer and therefore further away than expected as compared to the nearby (local) supernovae.

Standard luminosities of type Ia supernovae helped the researchers to determine their distances, while the observed redshifts provided an estimate of their recession velocities – the relation between redshift and distance helped the researchers to determine the expansion rate (km/s/Mpc) of the Universe.

Remote measurement yields an expansion rate of 46 km/s/Mpc (Blanchard et al. 2003) which is much lower than the local measurement of 72 km/s/Mpc by the Hubble Key Project (Freedman et al.).

The expansion rate (km/s/Mpc) for remote supernovae is lower than the expansion rate for local supernovae, therefore, we say that the Universe is accelerating now and had a slower expansion in the past.

According to Durrer (2011), “our single indication for the existence of dark energy comes from distance measurements and their relation to redshift”.

Working on research made me analyse the data. The peer-reviewed paper presents a novel interpretation of the redshift-distance relationship of observed supernovae as reported by the scientific reviewer of one of the most prestigious astronomy journals.

I believe accelerating Universe is a surprising discovery due to an undiscovered aspect.

https://www.researchgate.net/publication/343484700

"Accelerating Universe - The Surprising Discovery due to an Undiscovered Aspect"

What if the expansion is only apparent? For example, if you accelerate towards the speed of light, your experience of time changes. The result is you believe you were able to travel 1 lightyear in less than 1 year, therefore the universe appeared to contract in the direction of your travel. Although travel at the speed of light is theoretically impossible, travel at substantial percentages would result in the "expansion" slowing down and ultimately reversing to a contraction. The final speed of your ship would determine the perceived distance to your destination. While those on Earth will not see a change in distance (other than the apparent increase in distance due to the apparent expansion), you will not observe the same expansion in the direction of your travel. The shift in perception has to do with relativistic effects resulting from an increase in linear energy in the direction of travel. However, since nobody has actually attempted this feat, the question to be answered is whether that increase in energy would result in a contraction in all directions, or just in the direction of travel. Additionally, even if it only contracts in the direction of travel, the fact that clocks at different energy levels run at different speeds (experience time differently) suggests "time" and therefore "spacetime" depends on the total energy of the observer. The follow-on question would be: What if the apparent expansion is due to a decrease in our total energy levels that we are unable to measure? If we are "winding down" or moving towards increased entropy, how would be know? What if the apparent expansion is simply an indirect measure of our decreasing energy level?