Dark Energy is Real. Really?

I don’t have much time to post today after spending all morning in a meeting about Assuring a Quality Experience in the Graduate College and in between reading project reports this afternoon.

However, I couldn’t resist a quickie just to draw your attention to a cosmology story that’s made it into the mass media, e.g. BBC Science. This concerns the recent publication of a couple of papers from the WiggleZ Dark Energy Survey which has used the Anglo-Australian Telescope. You can read a nice description of what WiggleZ (pronounced “Wiggle-Zee”) is all about here, but in essence it involves making two different sorts of measurements of how galaxies cluster in order to constrain the Universe’s geometry and dynamics. The first method is the “wiggle” bit, in that it depends on the imprint of baryon acoustic oscillations in the power-spectrum of galaxy clustering. The other involves analysing the peculiar motions of the galaxies by measuring the distortion of the clustering pattern introduced seen in redshift space; redshifts are usually denoted z in cosmology so that accounts for the “zee”.

The paper describing the results from the former method can be found here, while the second technique is described there.

This survey has been a major effort by an extensive team of astronomers: it has involved spectroscopic measurements of almost a quarter of a million galaxies, spread over 1000 square degrees on the sky, and has taken almost five years to complete. The results are consistent with the standard ΛCDM cosmological model, and in particular with the existence of the  dark energy that this model implies, but which we don’t have a theoretical explanation for.

This is all excellent stuff and it obviously lends further observational support to the standard model. However, I’m not sure I agree with the headline of press release put out by the WiggleZ team  Dark Energy is Real. I certainly agree that dark energy is a plausible explanation for a host of relevant observations, but do we really know for sure that it is “real”? Can we really be sure that there is no other explanation?  Wiggle Z has certainly produced evidence that’s sufficient to rule out some alternative models, but that’s not the same as proof.  I worry when scientists speak like this, with what sounds like certainty, about things that are far from proven. Just because nobody has thought of an alternative explanation doesn’t mean that none exists.

The problem is that a press release entitled “dark energy is real” is much more likely to be picked up by a newspaper radio or TV editor than one that says “dark energy remains best explanation”….

Human Life’s Mystery

We sow the glebe, we reap the corn,
We build the house where we may rest,
And then, at moments, suddenly,
We look up to the great wide sky,
Inquiring wherefore we were born…
For earnest or for jest?

The senses folding thick and dark
About the stifled soul within,
We guess diviner things beyond,
And yearn to them with yearning fond;
We strike out blindly to a mark
Believed in, but not seen.

We vibrate to the pant and thrill
Wherewith Eternity has curled
In serpent-twine about God’s seat;
While, freshening upward to His feet,
In gradual growth His full-leaved will
Expands from world to world.

And, in the tumult and excess
Of act and passion under sun,
We sometimes hear-oh, soft and far,
As silver star did touch with star,
The kiss of Peace and Righteousness
Through all things that are done.

God keeps His holy mysteries
Just on the outside of man’s dream;
In diapason slow, we think
To hear their pinions rise and sink,
While they float pure beneath His eyes,
Like swans adown a stream.

Abstractions, are they, from the forms
Of His great beauty?-exaltations
From His great glory?-strong previsions
Of what we shall be?-intuitions
Of what we are-in calms and storms,
Beyond our peace and passions?

Things nameless! which, in passing so,
Do stroke us with a subtle grace.
We say, ‘Who passes?’-they are dumb.
We cannot see them go or come:
Their touches fall soft, cold, as snow
Upon a blind man’s face.

Yet, touching so, they draw above
Our common thoughts to Heaven’s unknown,
Our daily joy and pain advance
To a divine significance,
Our human love-O mortal love,
That light is not its own!

And sometimes horror chills our blood
To be so near such mystic Things,
And we wrap round us for defence
Our purple manners, moods of sense-
As angels from the face of God
Stand hidden in their wings.

And sometimes through life’s heavy swound
We grope for them!-with strangled breath
We stretch our hands abroad and try
To reach them in our agony,-
And widen, so, the broad life-wound
Which soon is large enough for death.

by Elizabeth Barrett Browning (1806-61)