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Time Traveling In The Past By Looking At The Sky

In life, we look at everything around us updating in real-time. looking up at the night sky is something else.

By Arunava Ch.Published 3 years ago 7 min read
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Time Traveling In The Past By Looking At The Sky
Photo by Vincentiu Solomon on Unsplash

When we look at the stars we're actually looking at the past, we aren't seeing the stars, or really anything in the universe as they currently are. We're seeing them as they were.

This all comes down to the way that light travels through space. Understanding space-time and why light moves the way it does means that one day we could look so far into the cosmos, we will be able to see the very first light at the birth of the universe, nearly 13.8 billion years ago.

And, in fact, there are astronomers and cosmologists working on this right now. The most important point you need to remember is that light travels at a constant speed, which means that it takes time to get anywhere.

So if you look up the Big Dipper,

image source: pinterest

the stars are anywhere from 79 to 125 light-years away. That means that what you're seeing is really the light that left the star 79 or more years ago, when you look up and see the moon, that's what it looked like 1.3 seconds ago. Same idea with planets, and it works in reverse too. If you looked at Earth through a super powerful telescope,

Spiral galaxy NGC 4845

from a galaxy 65 million light years away, you would see the earth as it was 65 million years ago, or around the time that T rex went extinct.

Thinking about the speed of light isn't a new concept, there's some evidence that scholars in 14th century India were exploring the speed of Sunlight. They thought of light as a sort of wind, and though they couldn't prove anything concretely, when converted into modern units, ancient calculations came surprisingly close to the actual speed of light. Today, we've calculated that speed down to the nanosecond.

Light speed applies here on earth too just in much smaller distances. If you look at an object one meter away from you, you're seeing it as it was three billionths of a second ago. This might seem too small to even matter. After all, it's impossible for us to discern three billionths of a second. But when we talk about space, those distances are so immense that the speed of light creates huge gaps in observational time.

So what does this mean for astronomers making observations of the stars? Well, it makes things a lot more complicated, especially since the universe is expanding

stretching fabric of the universe

the stretching of the fabric of the universe ever outward affects the light travelling through it. Another way I like to say this is that the light sticks to the fabric of space-time as the fabric of the universe expands, so to the waves of light. This is what's known as the Doppler effect.

Image source: huwaeii forum

It's the same reason why ambulance sirens seem to get higher and pitch, as it passes you. The waves are getting shortened, and then stretched out again.

With light, it's the color of each wavelength changes as the object gets farther away, and the light waves are more stretched out.

light wave length

This is what's known as redshift. Red because the longer the wavelength, the more red the light appears. At some point the waves get so long, they no longer appear as visible light, and slip into infrared.

Redshift isn't something you can see with the naked eye, as it only applies for objects that are really far away, and the change in hue is very slight. So, if you want to look at anything, really, really far away into the universe, you would need to account for the redshift.

This is why the Hubble Space Telescope, was built to see a small portion of the infrared spectrum. In 2016, Hubble observed a galaxy 32 billion light years away,

Galaxy GN-z11

but since this galaxy is so far away and the universe has been stretching since the light first left it, we're really looking at the galaxy as it was 13.4 billion years ago,

I know, leave it to the universe to make things more complicated.

This is the closest we've come to observing the birth of the universe. This galaxy GNZ-11 is located near Ursa Major, but even if you squint as hard as you can, you still won't be able to see it, unless of course you have some seriously impressive infrared super vision. Oh, and you'd have to be floating above Earth, because our atmosphere blocks some of the infrared.

Now, telescopes are getting even better, so much so that they may one day,

James Webb Space Telescope

even be able to see the beginning of the universe.

Thinking about the beginning of the universe as we know it. We're thinking of stars and galaxies, and that's a little bit later in the universe.

Big Bang expansion

Not very much though. And so, to see that, we actually might have a chance with these future telescopes and we might be able to see the supernovae of the first stars, we might be able to find the first galaxies ever.

The galaxies we're seeing today existed about a billion years after the Big Bang. So to kind of translate that that's about 13 billion years ago from our present day. And in order to observe these galaxies, accounting for redshift is super important. Light is all getting stretched and shifted to longer and longer wavelengths.

Britannica

So, because that's such a vast distance the light we see from these galaxies from the ultraviolet is actually in the near infrared, which is hard to see, That means that you need telescopes, and instruments that are sensitive to that and working from the ground is really hard in the near-infrared, then you need a space telescope. So we're really always pushing the limitations of what the current technology can give us.

The James Webb Space Telescope is going to be a serious game changer for these kinds of observations,

big bang time frame

because it will observe from outside Earth's atmosphere and specialize partly in the infrared. While we wait for these findings about the early universe, remember that every time you look at the stars, you're seeing back in time, and looking up at Ursa Major you can imagine how the Earth would look in reverse.. Pretty incredible right?

Thank you so much for reading. I know that the more I learned about astronomy, the more questions I have, so please let us know what else you'd like me to cover down in the comments.

Thanks to the following resources this article became a reality.

High-Redshift Astronomy - Taylor Hutchinson

“I work with galaxies that existed less than one billion years after the Big Bang, at redshifts of z 5. To give an idea of how long ago that is, current cosmology places the age of the Universe at approximately 13.7 billion years old. These young galaxies are so distant that their rest-ultraviolet (rest-UV) emission lines have been redshifted into the near-infrared (NIR). To measure the rest-UV spectrum of these sources requires sensitive NIR spectrographs on some of the world's largest telescopes. We call this redshift range the ‘Epoch of Re ionization’”.

https://aibhleog.github.io/research.html

Redshift and Hubble’s Law

“In 1929, Edwin Hubble announced that almost all galaxies appeared to be moving away from us. In fact, he found that the universe was expanding - with all of the galaxies moving away from each other. This phenomenon was observed as a redshift of a galaxy's spectrum. This redshift appeared to be larger for faint, presumably further, galaxies. Hence, the farther a galaxy, the faster it is receding from Earth.”

https://starchild.gsfc.nasa.gov/docs/...

What is the universe expanding into?

“When we think of space in everyday life, we don't think of it as something which is capable of stretching. Space, to us, just seems like something which is there, and which everything else in the universe exists within. But according to Einstein's theory of general relativity, space isn't really as simple as our common sense tells us. If we want to understand the actual way that the universe functions, we need to find some way to incorporate Einstein's ideas into our mental picture and imagine space as a more complicated entity which is capable of doing things like ‘bending’ and ‘stretching’”.

http://curious.astro.cornell.edu/abou...

astronomy
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About the Creator

Arunava Ch.

Hi 🖐🤓

I am a 22 year old boy(2021) interested in Science and Astronomy loved by my mother & brother👩‍👦‍👦

Following my passion for writing

Any amount of tip from you will be massively appreciated🙂🙏

Also, I'm working on my coding skills😉

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