Where our Universe is headed: the final frontier

neously created, given enough energy, but also antiparticles and unstable particles as well, resulting in a primordial particle-and-antiparticle soup. Yet even with these conditions, only a few speci c states, or particles, can emerge.

Before stars or galaxies formed, the Universe was full of light-blocking, neutral atoms. While most of the Universe doesn’t become re-ionized until 550 million years afterwards, with some regions achieving full reionization earlier and others later. e rst major waves of re=ionization begin happening at around 250 million years of age, while a few fortunate stars may form just 50-to100 million years after the Big Bang. With the right tools, like the James Webb Space Telescope, we may begin to reveal the earliest galaxies.

e galaxy cluster Abell 370 was one of the six massive galaxy clusters imaged in the Hubble Frontier Fields program. Since other great observatories were also used to image this region of sky, thousands of ultra-distant galaxies were revealed. By observing them again with a new scienti c goal, Hubble’s BUFFALO (Beyond Ultra- deep Frontier Fields And Legacy Observations) programme will obtain distances to these galaxies, enabling us to better understand how galaxies formed, evolved, and grew up in our Universe.

from now, the Universe will be slightly larger. But those subtle changes both build up over large, cosmic timescales, and a ect more than just distances.

As the Universe expands, the relative importance of radiation, matter, neutrinos, and dark energy all change. e temperature of the Universe changes. And what you’d see in the sky would change dramatically as well. All told, there are six di erent eras we can break the Universe into, and we’re already living in the nal one.

A Universe that has been around longer, therefore, will have expanded more. It will be cooler in the future and was hotter in the past; it was gravitationally more uniform in the past and is clumpier now; it was smaller in the past and will be much, much larger in the future.

By applying the laws of physics to the Universe, and comparing the possible solutions with the observations and measurements we’ve obtained, we can determine both where we came from and where we’re headed.

time as far as what reaches us. We will need to probe to fainter brightnesses and longer wavelengths to continue to see the objects presently visible, but those are technological, not physical, limitations.

e quantum uctuations that occur during in ation get stretched across the Universe, and when in ation ends, they become density uctuations. is leads, over time, to the large- scale structure in the

Universe today, as well as the uctuations in temperature observed.

At the high temperatures achieved in the very young Universe, not only can particles and photons be sponta-