Look to the Big Bang with Lisa

About 13.82 billion years ago, matter, space and time are said to have emerged from an infinitely tiny and hot point – that’s what the theory of the Big Bang says. Even though the term sounds like a short, gigantic explosion, the theory describes a long period of time in which space expanded rapidly. After that, the universe is said to have cooled down. However, the traces of the original heat can still be measured today as cosmic background radiation.

Thanks to space telescopes, we can now take a deep look into the past of our universe. James Webb has already discovered highly developed galaxies that should not have existed so soon after the Big Bang. We cannot see the starting point, the actual bang, at least not with telescopes that capture light.

This could perhaps change with the Lisa project (Laser Interferometer Space Antenna) from the European space agency Esa: three satellites that form a gigantic observatory for research into gravitational waves. The edge lengths of the equilateral triangle are each 2.5 million kilometers.

Karsten Danzmann is director of the Max Planck Institute for Gravitational Physics and an expert when it comes to the detection of gravitational waves and the development of the laser technologies required for this. He played a key role in developing Lisa.

The astrophysicist explains the problem with telescopes that are aimed at visible light: With them you can “not look further back than around 370,000 – 400,000 years after the Big Bang. Before that, the world was so hot and so dense that photons, i.e. the light particles, couldn’t get through.” Things are different with gravitational waves. These are hardly scattered and with them “we can see to the beginning.” That would be completely new territory, because “We don’t know what the beginning is and where it was.”

“However, gravitational waves can only be researched to a limited extent from the earth because you have to hear them. “What we hear from the earth are gravitational waves at high frequencies, namely at frequencies of a few hertz to a few kilohertz,” says Danzmann .

However, since everything on earth is noisy, low frequencies cannot be adequately isolated. “To do that, they have to go somewhere quiet. And where is it quiet? Where there’s nothing. Up there in space.”

From Earth we can hear objects the size of a few solar masses and tiny things. But at the beginning of the universe there are “galaxies and many other objects that have not one solar mass, but thousands, millions, billions. These are the superheavy black holes.” Every galaxy appears to harbor such a supermassive black hole at its center.

They may have dominated the universe before galaxies were formed, at the beginning of time. Danzmann suspects that they are responsible for “the structure in our world emerging as it is today.” The three satellites of the Lisa project can be used to detect the low frequencies that such objects emit.

The Big Bang theory is currently one of the most plausible hypotheses when it comes to the creation of our universe. However, there are also other promising theories, such as the Big Bounce. Here the Big Bang is just the result of the collapse of a previous universe.

This collapse is called the Big Crunch, in which the universe collapses under the effect of gravitational force. Instead of expanding, the universe collapses and disappears. In the case of the Big Bounce, this process – of expansion and collapse – is supposed to repeat itself ad infinitum.

LISA could provide evidence for the appropriate theory and the actual formation of our universe. “And if we haven’t heard the Big Bang yet, then we’ll build the next mission and it’s ten times more sensitive,” says Danzmann optimistically.

In 2035, the three Lisa satellites will be launched into space with an Ariane 6 rocket. It will take another two years for the first data to reach Earth. In order to analyze all the data, a lot of computing power is required. This will be a challenge with current supercomputers.

But here too, Danzmann is optimistic: “We still have 15 years to build the corresponding computer. It will be fine.” He has experience with long periods of time: Danzmann wrote the first proposal for LISA 31 years ago. At a time when gravitational waves were not yet considered confirmed. It was only in 2015 that two postdocs were the first people to ever hear it – in the building opposite Danzmann’s office.

The waves were recorded by the Ligo (Laser Interferometer Gravitational-Wave Observatory) in the USA. “It was 11:50 a.m. on a Monday afternoon and the two postdocs were doing what they always do: They wanted to go out to dinner,” remembers Danzmann. They still had ten minutes until then and decided to see what the ongoing Ligo experiment had recorded so far. “And suddenly they heard waves.”