Date: June 17, 2010
Title: How Did the Universe Form?
Podcaster: Stuart Clark
Description: The biggest bang of them all started the Universe, but how much of it can we still see today?
Bio: Dr Stuart Clark is an award-winning astronomy author and journalist. His books include The Sun Kings, and the highly illustrated Deep Space, and Galaxy. His next book is Big Questions: Universe, from which this podcast is adapted. Stuart is a Fellow of the Royal Astronomical Society, a Visiting Fellow of the University of Hertfordshire, UK, and senior editor for space science at the European Space Agency. He is also a frequent contributor to newspapers, magazines, radio and television programmes. His website is www.stuartclark.com and his Twitter account is @DrStuClark and his Twitter account is @DrStuClark
Today’s sponsor: Between the Hayabusa homecoming from Itokawa and the Rosetta flyby of asteroid Lutetia, 13 June until 10 July 2010, this episode of “365 Days of Astronomy” is sponsored anonymously and dedicated to the memory of Annie Cameron, designer of the Tryphena Sun Wheel, Great Barrier Island, New Zealand, a project that remains to be started.”
Additional sponsorship for this episode of 365 Days of Astronomy is provided by Chuck McCorvey.
HOW DID THE UNIVERSE FORM?
Hello I’m Dr Stuart Clark, astronomy author and journalist. Today I’d like to explore the question: How did the Universe form?
It seems barely credible, but the definitive proof of the Universe’s moment of creation was first dismissed as pigeon droppings. In 1964, two researchers from Bell Laboratories, New Jersey, picked up a strange signal through a radio telescope. Having rejected interference from nearby New York, they noticed a pair of nesting pigeons had peppered the device with droppings. So they cleaned the telescope, and transported the birds away. The pigeons returned however, and this time the astronomers weren’t so charitable. The bird were despatched by shotgun and the telescope scrubbed clean again. Yet still the mysterious signal remained. The researchers, Arno Penzias and Robert Wilson, began to think that it might be coming from space.
Unknown to them, a group of astronomers had predicted its existence almost two decades earlier. In 1948, the Ukrainian physicist George Gamow had been exploring the consequences of Georges Lemaître’s 1927 idea that the entire Universe exploded from a single compacted ‘atom’. Gamow calculated that, if the Universe began with nothing but the simplest chemical element, hydrogen, then the intense heat of the big bang would have fused a quarter of it into helium: almost the exact proportions astronomers were seeing. He predicted that radiation from the forging of helium would be lingering as an all-pervasive blanket of microwaves. Cosmologists quickly realised that Penzias and Wilson had discovered the residual radiation from the big bang.
Current physics cannot deal with the tiny fractions of time and space that would need to be considered at the beginning of the big bang. The smallest unit of time that physics can presently handle is 10-43 seconds: a decimal point followed by 42 zeros and a one. This is known as the Planck time, after Max Planck, the father of quantum theory. During the Planck time, everything that we see in the Universe today was squeezed into a tiny dot, smaller than an atomic nucleus. The four fundamental forces of nature – gravity, electromagnetism and the strong and weak nuclear forces – were indistinguishable from one another, and the ‘dot’ was already expanding. To fully picture the Planck era, a theory of quantum gravity is needed, but as yet this remains elusive. As the era ended, so gravity became a distinct force and physics as it is presently understood took over.
Temperature and pressure were so extreme that matter and energy were entirely interchangeable; particles would form spontaneously including unusual stuff: antimatter.
British physicist Paul Dirac discovered an equation that correctly described the behaviour of electrons moving at high speed, but predicted that ‘mirror-image’ electrons should exist as well, identical in mass but carrying a positive charge instead of negative. Four years later came the experimental proof, with the discovery of a positively charged electron (later called a positron). It was discovered in a shower of particles coming from space. Dirac extended the idea to all particles of matter, and coined the umbrella term of antimatter. Should it run into its mirror-image piece of matter, both will transform into pure energy, giving out a pair of gamma rays.
But if antimatter is always created, why is there any matter left in the Universe? The solution is bizarre and as yet unexplained but it seems that for every billion particles of ordinary matter created after the big bang, there were only 999,999,999 particles of antimatter formed. These annihilated with the corresponding matter, producing the energy that became the microwave background radiation, and leaving single orphaned particles of matter that built up into the stars and planets of today.
Cosmologists believe the Universe then underwent a sudden intense expansion that they call inflation, which drove the Universe to balloon by a factor of 1050 in a time of just 10-32 seconds. This would solve two thorny cosmological problems.
The first is the horizon problem. The energy carried by the microwave radiation governs the temperature of space by heating any molecule or atom that gets in its way to the same temperature of about –270.3 degrees Celsius. The conundrum is why the temperature should be the same everywhere. The opposite sides of the Universe haven’t had time to exchange energy and so equalize their temperature. The inflation theory helps by stating that the entire volume of our Universe came from a vanishingly small region that suddenly grew in size and spread the same temperature across space.
Second is the flatness problem. Einstein’s proposition that matter curves the fabric of space means that the Universe should have an overall curvature, determined by the total amount of matter and energy it contains. But as far as anyone can tell, on the largest scale the Universe is completely ‘flat’. Again, inflation can solve it because the intrinsic curvature has been spread so far we can no longer perceive it. Like the way the ground beneath out feet appears flat even though we know the Earth is spherical.
The question remains as to why the Universe would have inflated. It may be linked to the way the strong nuclear force ‘broke away’ from the electroweak force producing energy to drive the inflation, but this is uncertain and the subject of much debate between physicists.
When calculations reach a millionth of a second after the big bang, there is more confidence about what was going on. This is because powerful particle accelerators, such as the Large Hadron Collider in Switzerland, can re-create the high-temperature, high-pressure conditions by smashing particles together with great energies and analysing the debris.
At a microsecond, the Universe was filled with subatomic particles called quarks, together with antiquarks and gamma-ray photons. Quarks gathered together to form protons and neutrons, which in turn went on to form the atomic nuclei of today. The Universe continued to expand, although less rapidly, lowering the density of matter and energy, reducing the temperature and pressure. Two seconds after the big bang, the electroweak force separated into the weak nuclear force and electromagnetism. At about three minutes, the era of nucleosynthesis began. This is the period George Gamow investigated mathematically during the 1940s.
For a dozen minutes, the entire Universe was similar to a star’s hot, dense interior and protons and neutrons combined to form helium and lithium nuclei. The Universe then entered a relatively calm phase, creating a state of matter called plasma. Plasmas exist today inside stars and in clouds of gas surrounding high-mass stars; in the early Universe the plasma stretched across all space.
After a year, collisions were generally less frequent as the expansion gave the particles more room. But gravity began pulling particles into clumps. Around 380,000 years after the big bang a watershed was reached − the decoupling of matter and energy, in which electrons were now lethargic enough to be captured by atomic nuclei.
Neutral atoms of ordinary matter formed, and the Universe became transparent because most photons could now travel all the way across space without running into an absorbing particle. They made a powerful sleet of X-rays; eventually redshifted by the expanding Universe to become the microwave background detected by Penzias and Wilson.
Maps of the microwave background radiation in all directions have been analysed and found to contain minuscule temperature variations, of a hundred-thousandth of a degree. These ‘anisotropies’ are the imprints left by the clumps of matter formed in the early Universe, and signpost the seeds from which galaxies and the large-scale structure emerged.
To get an earlier snapshot of the Universe, astronomers must turn to neutrinos, which would have been released about two seconds after the big bang, the moment when the weak force separated from the electromagnetic force. Far more difficult to observe than microwaves, neutrinos slip through ordinary matter. In the time it has taken you to listen to this podcast, billions of them have passed through you, the Earth and out the other side.
Calculations during the 1930s proposed neutrinos but it took three decades before a purpose-built detector captured one. Current detectors are buried in the Antarctic ice, or sunk below the surface of the Mediterranean Sea, scanning ice or seawater for the faint flash that betrays each neutrino’s passage. Unfortunately it’s not the low-energy neutrinos given out two seconds after the big bang that are being mapped, but high-energy ones generated from the explosion of stars. Nevertheless, it’s a step towards grabbing a picture of the two-seconds-old Universe.
The ultimate picture of the big bang may be possible if physicists can unify the forces and deduce the nature of gravitons, the particles suspected to carry quantum gravity. By analogy with the weak nuclear force and neutrinos, the separation of gravity at the end of the Planck era would have generated a background of them. A future graviton telescope, if such a thing is possible, could detect it and give a picture of the Universe just 10-43 seconds after the big bang.
Now that’s something cosmologists everywhere would like to see.
End of podcast:
365 Days of Astronomy
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