BBC Science The Theory of (nearly) Everything 2019

THE STORY OF THE UNIVERSE

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A baffling find by Arno

Penzias and Robert Wilson

that the Universe was

warmer than it should be

earned them a Nobel Prize

THE KEY

EXPERIMENT

The Horn Antenna at Crawford Hill in New

Jersey was built for use with satellites, so

the shape of it was designed to minimise

interference from the ground and provide

the best possible measurement of the

strength of radio noise from the sky.

The nature of this radiation depends on

the temperature of the radiating object. The

amplifiers used in the receiver were cooled

to 4.2 Kelvin (-268.8°C) using liquid helium,

and Penzias devised a ‘cold load’, cooled by

liquid helium to about 5 Kelvin, which was

used to calibrate the system.

By switching the antenna from

observations of the cold load to observations

of the sky, they could measure the apparent

temperature of the Universe (expected to be

0 Kelvin), then subtract out known factors,

such as the interference from the atmosphere

above. But in 1964 it soon became clear that

the radiation coming from the antenna into

the receiver was at least 2 Kelvin hotter than

they could explain. The pair did everything

they could think of to remove any sources

of interference, including cleaning out the layer

of droppings that had accumulated in the

antenna horn from a pair of nesting pigeons.

Nothing made much difference. The mystery

of the ‘excess antenna temperature’ continued

to baffle them throughout 1964.

That is until the pair realised, with the help

of Robert Dicke, James Peebles, Peter Roll and

Dave Wilkinson at Princeton, that what they

were looking at was the afterglow radiation

from the Big Bang.

Robert Wilson (left) and Arno Penzias (right) in front of the antenna that fortuitously

picked up the heat signature of the Cosmic Microwave Background

A map of the Cosmic Microwave Background

• the afterglow radiation of the Big Bang

But it may not spell the end for the

theory of inflation just yet. “My gut

instinct is that these anomalies point

to a more specific model of inflation,”

says Dr Rose Lerner, a cosmologist at

the University of Helsinki in Finland,

who works independently of the

Planck consortium.

Another solution to the anomalies,

according to Prof Matthew Kleban of

New York University, is that during

the sudden expansion that happened

during inflation, our Universe

slammed into a neighbouring one.

This sent shockwaves rippling

through our cosmos that imprinted

the anomalies we see today. If so, we

should t hink of t hem as a cosmic

bruise. Testing such a controversial

idea, however, is very tricky.

CHAPTER 3: PARTICLE CREATION

1 minute after the Big Bang

At one minute old, the entire Universe

resembled the interior of a star – but

on a vast scale. Particles that would

become the nuclei of all the atoms

in the Universe were built in this

cauldron. Mostly these were single

protons that would become hydrogen,

but around a quarter of the particles

transformed into helium nuclei,

containing two protons and two

neutrons. Trace amounts of lithium

and beryllium were also produced.

The evidence for all of this furious

activity is all around us today in the

chemical make-up of the Universe.

We k now f rom measu rements of t he

radiation given off by our Sun and

other stars that 98 per cent of the 5