The end of the Copernican Principle?


One of the most important philosophical ideas in science, particularly in Astronomy and Cosmology, is the “Copernican Principle”. In its shortest form it states “We are not special”. The idea that human beings are not in a privileged reference frame was the underlying idea behind the Copernican revolution (in which science came to understand that the Earth is not the center of the Universe.)

Much of modern science depends on this idea, often in unspoken ways. We assume that physics works the same in all labs here on earth for instance when we expect scientific results to be reproducible and verifiable. If the Gravitational constant was different in China than it is in Brazil this wouldn’t be the case. We assume that fusion works the same on the Earth as it does in Sun. And the same in the Sun as it does in Alpha Centari and as it does in giant blue and uv stars formed right after the big bang. We assume that galactic dynamics are the same in all galaxies…

Break this chain of reasoning and suddenly everything becomes questionable and our ability to explain phenomenon starts to fail. So it’s never been really challenged since it was broadly accepted as a result of Kepler’s and Galileo’s use of Copernicus’ ideas.

Except there’s a problem. The application of the strict Copernican principle, which would say that physics works the same everywhere and at every era of cosmological history, is taking us to a place in Cosmology where we’re inventing all sorts of complicated ideas to explain observations that seem to indicate the Universe is accelerating in its expansion, that it’s primarily made of some sort of Dark Matter that we can’t yet detect, and that Dark Energy automatically seems to violate a fundamental conservation law.

Seems sort of epicyclical in its complexity doesn’t it?

Now apparently some cosmologists looking at this scandalous structure (and more than that) have asked the question “What if the Copernican Principle isn’t as strict as we’ve insisted?”

They specifically decided to test the consequences of this idea by seeing what happens in one of the scandals of modern cosmology, the prediction of elemental abundances. Right now the standard models of the big bang predict that there should be about 3x as much lithium in the Universe as we observe.

” Marco Regis and Chris Clarkson from the University of Cape Town in South Africa say they can explain this shortfall in lithium. What’s extraordinary, however, is that the same thinking also explains the supernova observations without any need for an accelerated expansion or dark energy.

Their new idea is that the lithium abundance can be explained by abandoning one of the fundamental assumptions of modern cosmology: the Copernican principle. This is the notion that humans have no privileged position in the universe. For cosmologists, this means that the universe must be more or less the same everywhere and on all scales.

Various cosmologists have pointed out that if we abandoned this principle, it would be straightforward to explain the supernova data. It simply means that the universe is not homogeneous on the very largest scale. Instead, we must be sitting at the centre of some kind of giant void in a much larger universe.”

Read the full article here.

This is a rather breath taking idea for scientists. To some extent Relativity, which states as one of its fundamental assumptions that there can be no privileged or special reference frame is a systematic codification of the Copernican Principle. Relativity theory works pretty darn well and it’s been repeatedly verified, but not necessarily at the Cosmic scale.

There are interesting philosophical problems associated with this idea too I imagine. I wonder what Karl Popper would make of it.

Any rate, this is a particularly interesting idea. It’s much more elegant than having to modify newtonian gravity and other methods that have been suggested for fixing the scandalous observations of experimental cosmology. Elegance is often a sign that something is worth following up on in scientific circles. I expect we’ll be hearing more about this…

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Episcopal bishop, dad, astronomer, erstwhile dancer...

1 Comment

  1. Steve says

    I don’t know if I totally comprehend everything you share in this post, but I am amazed at the depth of your crtical scientific evaluation and thinking which has challenged my own critical and evaluative mind with only 2 years of college education years ago. In some respects I feel as if I have been awakened after being in a deep coma. WOW! is really all can say at the moment.

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