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Tuesday 7 October 2014

Cosmic Inflation, BICEP2 and Planck

Cosmic inflation is the exponential expansion of space in the early universe. In other words, how did the universe go from being so small at the time of the big bang to the size it is today?

But why do we even think this occurred? In the 1920's, astronomer Edwin Hubble noticed when looking at galaxies through a telescope, that the galaxies were actually moving away from one another. The further apart they were, the faster they moved.

The only logical explanation for this was that the universe was in fact expanding. If everything seemed to be moving away from each other in all sorts of directions, then surely at some point in the past, it must have been very small, hot and dense. This led to what we now know as the Big Bang Theory, so called because of the implication that the universe began a single point and exploded outwards.

time line of the universe, from big bang to today. Public domain image courtesy NASA.
The Big Bang is believed to have occurred 13.7 billion years ago, after which the universe rapidly expanded in a period of time we call Inflation. Scientists are still searching for conclusive evidence of this, and seek to test the two fundamental assumptions upon which it is based; that the same physical laws apply everywhere in the universe, and that on large scales on large scales the universe is homogeneous and isotropicImage credit: NASA (public domain)

Everywhere we look in the universe, we see billions of galaxies evenly spread. Up until 1979, nobody could explain why this was. That was until a young cosmologist by the name of Alan Guth put forward a possible solution to the problem; he called it inflation.

Guth proposed that near the start of time, the universe went through a phenomenal growth spurt, accelerating the expansion of the cosmos. Just ten million Planck times (0.00000000000000000000000000000000001 seconds) after the Big Bang, a very very small volume of space begins to expand at a much quicker rate than before. This inflation turned all the unimaginable chaos of the early universe into a space where objects' positions had been adjusted and fixed into place.

To give this some sort of context, it's like a grain of sand expanding to the size of the sun, faster than the speed of light.

But how do scientists go about trying to find evidence of this cosmic inflation? Well, back in 1964, two American astronomers noticed that while using their radio telescope they were receiving a strange humming sound. Unsure of what this was, the pair cleaned the telescope of bird droppings to ensure there weren't any outside influences on what they were picking up, but this was to no avail. If anything, the humming got louder. What they were listening to was not the effect of bird droppings on their instrument, but the sound of the afterglow of the fireball created by the Big Bang.

380,000 years after the Big Bang, the universe cooled enough to allow protons and electrons to come together and form matter. Ever since that moment, light has travelled uninterrupted through space, until it became detectable at Earth. Scientists named this radiation the Cosmic Microwave Background, and they believed that the secrets to inflation lay hidden in this light. Theoretically, this inflation should have produced gravitational waves that would ripple through the fabric of the universe.

That's why in 2009, the European Space Agency launched the Planck mission. What Planck did was effectively take the temperature of the universe, and try and prove that inflation was the best possible explanation as to why everything in the universe is so evenly distributed, after all that went on during and after the Big Bang.

Cosmic microwave background or CMB seen by ESA Planck spacecraft
Planck gave us this image of the temperature across the cosmos. The blue areas you see are cooler, and would turn out to be just empty voids in the vacuum of space. The green, yellow and red areas are warmer, facilitating the formation of stars and galaxies. Image credit: ESA and the Planck Collaboration

In a further attempt to try and fully understand the theory of inflation and gravitational waves, scientists using the BICEP2 telescope at the South Pole announced earlier this year that they had discovered evidence proving that both gravitational waves and inflation were no longer science fiction, but science fact! However, things seemed a bit too good to be true.

Investigating an area of the sky thought to be relatively free of photon interference, there's a known source of microwave photons that's pretty much everywhere - interstellar dust. Teams concluded from their analysis that what the telescope was really looking at was not the birth of our cosmos, but instead, the amount of space dust that was present in the area being observed.

At this stage you would think that to get a better scientific insight into inflation, that the Planck and BICEP2 teams would combine their findings. However, there is often a pressure to be the first with such a major finding, and it seems on this occasion that competition won out over co-operation.

All in all, even though inflation seems like the most plausible idea for the reasoning behind the accelerated growth of space, we are still unsure exactly what caused the biggest growth spurt in the history of time on the infant universe. However, sites like Things We Don't Know strive to help encourage investigators from rival teams to come together for the benefit of humankind's understanding, to help us all find the answer to humankind's greatest questions!

This guest article was written by Cian O'Regan to celebrate World Space Week 2014. Cian can usually be found writing for the Irish Space Blog.
why don't all references have links?

[1]Planck Collaboration Team (2014). "Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes". ArXiv. arXiv:1409.5738.

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