The cosmic time machine: how the James Webb Space Telescope allowed us to see the universe's first galaxies
It’s been an exciting week with the release of amazing photos of our Universe by the James Webb Space Telescope (JWST). Images like the one below give us the opportunity to see distant, faint galaxies as they did more than 13 billion years ago.
NASA, ESA, CSA and STScI
This is a great time to step back and appreciate our first class ticket to the depths of the Universe and how these images allow us to look back in time.
These images also raise an interesting point about how the expansion of the Universe factors into the way we calculate distances on a cosmological scale.
Modern time travel
Looking back in time may sound like a strange concept, but that’s what space researchers do every day.
Our Universe is bound by the rules of physics, with one of the best known “rules” being the speed of light. And when we talk about “light,” we are actually referring to all wavelengths across the electromagnetic spectrum, which travels at a speed of about 300,000 kilometers per second.
Light travels so fast that in our everyday life it appears instantaneous. Even at these breakneck speeds, it would still take time to travel anywhere across the cosmos.
When you look at the Moon, you really see it as it was 1.3 seconds ago. It’s just a little peek into the past, but it’s still the past. It’s the same with sunlight, except that photons (particles of light) emitted from the Sun’s surface travel for more than eight minutes before they finally reach Earth.
Our galaxy, the Milky Way, spans 100,000+ light years. And the beautiful newborn stars seen in JWST’s Carina Nebula image are 7,500 light-years away. In other words, the nebula as described is from about 2,000 years earlier than when the first writings are thought to have been found in ancient Mesopotamia.
NASA, ESA, CSA and STScI
Every time we look away from Earth, we look back at the past as before. This is a superpower for astronomers because we can use light, as it is observed all the time, to try to solve the mysteries of our universe together.
What makes JWST spectacular?
Space-based telescopes allow us to see certain ranges of light that cannot pass through Earth’s dense atmosphere. The Hubble Space Telescope is designed and optimized to use the ultraviolet (UV) and visible parts of the electromagnetic spectrum.
JWST is designed to use a wide range of infrared light. And this is the main reason JWST can look further into the past than Hubble.
NASA, J. Olmsted (STScI)
Galaxies emit a variety of wavelengths on the electromagnetic spectrum, from gamma rays to radio waves, and everything in between. All of this gives us important information about the various physics going on in the galaxy.
When galaxies are near us, their light hasn’t changed much since they were emitted, and we can investigate these various wavelengths to understand what’s going on inside them.
But when the galaxy is very far away, we no longer have that luxury. Light from the most distant galaxies, as we see them today, has been stretched to longer and redder wavelengths due to the expansion of the universe.
This means that some of the light that would have been visible to our eyes when it was first emitted had lost energy as the universe expanded. It is now in a completely different region of the electromagnetic spectrum. This is a phenomenon called the “cosmological redshift”.
And this is where JWST really shines. The range of infrared wavelengths that JWST can detect allows it to see galaxies that Hubble never could. Combine this capability with JWST’s large mirror and incredible pixel resolution, and you have the most powerful time machine in the known universe.
Read more: Two experts break down the first images of the James Webb Space Telescope, and explain what we’ve learned
Bright age is not the same as distance
Using JWST, we will be able to capture very distant galaxies as they were only 100 million years after the Big Bang – which happened about 13.8 billion years ago.
So we will be able to see light from 13.7 billion years ago. What will hurt your brain, however, is that the galaxies are not 13.7 billion light-years away. The actual distance to these galaxies today is ~46 billion light years.
This difference is all thanks to the expanding universe, and makes working on very large scales complicated.
The universe is depleting because of something called “dark energy”. It is considered a universal constant, acting the same in all planes of space-time (the fabric of our universe).
And the bigger the universe expands, the bigger the effect of dark energy on its expansion. This is why even though the universe is 13.8 billion years old, it is actually about 93 billion light years wide.
We cannot see the effects of dark energy at the galactic scale (within the Milky Way), but we can see it from much greater cosmological distances.
Sit back and enjoy
We live in an age of extraordinary technology. Only 100 years ago, we didn’t know there were galaxies outside our own. Now we estimate there are trillions, and we are spoiled for choice.
For the foreseeable future, JWST will take us on a journey through time and space every week. You can stay up to date with the latest news as NASA releases it.
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