We're all familiar with the sound of a car passing by.
This distinctive drop in Pitch is known as the Doppler effect
If light moved slow enough, we would also see the car change color as it passed us by.
The reality is, light moves far too fast for us to notice anything like this
But take a look at this image of Galaxy GS z13
it should look something like this, but its color has been changed all the way to Red.
In fact, the light from this galaxy has been changed so much, that it isn't even visible to the human eye.
This is the Doppler effect in action or for light, it's known as redshift.
In this video we're going to look at this newly discovered Galaxy
and how we are able to see almost right back to the start of our Universe.
We'll also be giving away this awesome space shuttle Lego set, so stick around to the end of the video
to see how you could win.
Although it may not look like much, this tiny red blob is the most distant thing anyone has ever seen.
With this picture we are looking back 13.6 billion years into the past
when the universe was only two percent of its current age.
But the Galaxy itself is over 33 billion lightyears away. How does this make sense?
We know that a lightyear is the distance light travels in a year, so if it took the light 13 billion years to reach us
it should be 13 billion lightyears away.
Well it's not quite as simple as that.
In the time that light has spent traveling toward us, space itself has been constantly expanding
and the galaxy has been moving further away from us.
Because of this, the Galaxy in 2023 is now over 33 billion lightyears away
but its light from 13 billion lightyears away has only just reached us.
But how could we possibly measure this distance?
The answer lies within the color of the Galaxy.
All of the light we see is just a small fraction of the light that actually exists.
Every form of light can be thought of as a wave
and the length of that wave can be smaller or longer; this is what determines the colors that we see.
But our eyes are very limited, and so there is much more light bouncing around us that we simply can't see.
So when we discover a Galaxy that has changed color, something must have happened to it.
Just like the moving car, the light from this Galaxy is being changed or redshifted
but there are two kinds of redshift; Doppler redshift and cosmological redshift.
In the Doppler scenario, the Galaxy is moving through space, but with cosmological redshift
the Galaxy is both moving and stationary at the same time - we'll get to that one later.
First, let's imagine the Galaxy as if it was stationary. The light leaves the Galaxy in every direction
at a constant speed.
When the Galaxy moves through space the waves at the front get slightly compressed
and the waves at the back get stretched out. Since it's traveling away from us, we are receiving the
stretched light which has a longer wavelength and therefore a different color.
But why is the galaxy moving in the first place?
The planets in our solar system have movement, our solar system has movement
and our galaxy itself is also moving through space, but this isn't enough to see a dramatic effect in redshift
since this relative movement is nowhere near the speed of light. But remember that this
galaxy has gone from 13 billion lightyears to over 33 billion lightyears away - a distance only possible
if it was going considerably faster than the speed of light.
Understanding how this happened is pretty complicated
but understanding the basics of our solar system, is really easy
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Since the Big Bang nearly 14 billion years ago, our universe has been constantly expanding
but understanding what this actually means is pretty difficult. We Imagine the Big Bang is an explosion
that radiates out from a central point, but in reality there is no center of the universe
and no single point where space expands from.
If you take any point in the universe, everything will appear
to be expanding away from it at the same rate. It's not that planets, stars, or galaxies are getting bigger
but the space between those galaxies is getting bigger. The rate of this expansion
is around 70 kilometers per second for every 3 million lightyears of distance, so an object
at that distance will be 70 kilometers further away after a second, an object 3 million lightyears
further down the line will be 140 kilometers further away, and so on. If we extrapolate that out
to Galaxy GS z13, it will be moving away from us at around 7 hundred thousand kilometers per second
but we're told that objects can't move faster than the speed of light, but that is only true
for objects moving through space - this is where cosmological redshift comes in.
If we look at an unbaked cookie
we have a random scattering of chocolate chips which we can think of as galaxies
When the cookie gets baked, the dough expands and the chips end up further away from each other
but it's not that the chips have moved relative to the dough, but the dough in between the chips has
expanded just like our universe. The galaxies in our universe can't move through space faster than
the speed of light, but there is no limit to how fast the universe can expand.
This means that the light currently being emitted from this galaxy
will never reach us since the expansion of the universe at this distance is out- racing the speed .of light
but how do we know all of this? How do we know how far away this galaxy is?
Well, although our planets and galaxies don't grow with the expansion of space
light waves do. As the light from the galaxy has been traveling through space
the expansion of space itself has stretched this wave of light to a much longer wavelength, and so
by the time the light reached James Webb it had been stretched well outside of our normal viewing range.
But the James Webb Telescope was designed to view light in the infrared range, so it was
just capable of picking up this light. The trick to measuring how old and distant the light is
lies within measuring how much that light has been shifted.
So James Webb looked for galaxies whose light had been shifted the most.
It first focused on a tiny area of our night sky called the Ultra Deep Field.
This area is the equivalent of a coin placed 18 meters away, but it features over 100,000 galaxies
many of which have gone through a large amount of redshift, but the problem is that
James Webb's time is precious and it would take forever to survey every little dot in the galaxy.
So, in order to choose which galaxies to study it used something known as the Lyman technique.
Light with a wavelength below 90 nanometers gets completely absorbed by hydrogen - this shows up as
a dramatic drop-off at around here on the Spectrum. So below this, no light should reach us.
For that has been redshifted, that drop-off point will appear much further up the spectrum
and so by doing a relatively quick spectroscopy measurement, Webb found four galaxies
that all had a drop-off point that had been shifted all the way into the mid-infrared range
One of these was Galaxy Gsz13.
This galaxy had the highest amount of redshift that scientists had ever seen.
But calculating the exact redshift amount
is what allows us to find out how old and distant this galaxy is.
We can use the spectrum of light as a reference point. Light gets absorbed by various elements at
different wavelengths creating a signature on the spectrum - a recognizable pattern that will
be the same for all light. As the light from the galaxy gets redshifted, that signature will also be
shifted by the same amount. And so, with the light from Galaxy GS z13 we should see this signature
appear further up in the spectrum.
By taking specific points and measuring how much they have been shifted
divided by the original wavelength, we get an exact redshift value. This alone doesn't
tell us much, but after some complex calculations that are too long for this video, we can arrive at
the travel time - this is how long the light we see has been traveling through space to get to us.
We can calculate this because we already know some important characteristics about the universe.
We know that the universe is expanding and the rate at which it expands, and although this rate
is constant, galaxies actually accelerate away from us. This is because the rate at which galaxies move
away from us changes over distance and not time. When Galaxy GS z13 was much closer to us there was
less space in between us, therefore less space to expand. Now the space between us is much larger and
so there is much more expansion going on. And so by understanding how this expansion changes over time
we can calculate the light from this galaxy to be around 13.6 billion years old.
What is most shocking about all of this is just how much we can't see and will never see.
We talk about if there is life on Mars, but looking at the sheer scale of the universe we can't even see, it seems
completely inevitable that life exists somewhere out there.
And now for the Primal space giveaway.
The winner of the previous giveaway is Kirk Bryson. Congratulations! In the next video we'll
be giving away this awesome space shuttle Lego set. All you need to do is sign up at the link below,
leave a like on the video, post a comment with your thoughts on the possibility of life in our universe.
Thank you very much for watching and I'll see you in the next video.
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