By studying variable stars and measuring their distances from Earth, scientists are able to then calculate the velocity of these distant stars and galaxies. They also survey the spectral lines emitted by variable stars, which indicates the direction in which its moving.
It turns out that every single galaxy is red-shifted, which means that every galaxy in the known universe is moving away from ours. Hubble discovered that the farthest galaxies are moving the fasted, and described this relationship with the following equation:
v = (Ho) * d
where v is recessional velocity, d is distance, and Ho is a constant valued at 1.5 to 3.1 * 10^-15 parsecs per second. This constant is known as Hubble’s constant (which becomes important later, when calculating the age of the universe.)
In class, we were given a great example of Hubble’s Law that explains how we know the universe is expanding. Our teacher had drawn a cluster of random dots before class, and photocopied the image on transparent paper, expanding the same image more with each copy–but altering nothing but the size. A student picked a random dot to represent our galaxy, and our teacher aligned every copy so the dot that the student chose overlapped with each copy.
The example was repeated another time with a different dot, and both times, every “galaxy” could be observed moving away from the main dot. Every time the image was expanded, the farthest galaxies seemed to make the biggest jumps further away.
This example shows how we know the universe is expanding. It explains Hubble’s law and his observations about the farthest galaxies moving away from us the most quickly. It also shows that there is no center of the universe, because no matter which dot you choose to focus on, every other dot seems to run away from it. This is how we know the universe is expanding. But how do we know the age of the universe?
It’s simple. When we look out into space, we are looking out into the past, because it takes time for the light of distant objects to reach us. Currently, the farthest objects in the universe are 13.7 billion light years away–this is the value represented by Hubble’s constant. The universe began as a single point, and then suddenly began rapidly expanding in an event known as the “big bang.” Try thinking backwards. If the farthest away objects are 13.7 billion light years away, then 13.7 billion light years ago, they were in the same position as us, in the singular point where the universe began. Therefore, the universe is 13.7 billion years old.
An article I found on phys.org titled, “Astronomers measure universe expansion, get hints of ‘new physics,” explains how gravitational lensing and lights emitted from quasars are studied in order to gauge the age of the universe. The study resulted in an estimation of Hubble’s constant (and therefore the age of the universe) that is slightly different than what it’s normally calculated to be. This may be due to dark energy, which is the force that is thought to motivate the relentless expansion of the universe.
This relates to the conceptual objective because the different estimation shows that the universe is constantly expanding. It is also important because it shows that we are constantly learning new things about space that we didn’t know before. Not much is known about dark energy. And since the universe is infinitely expanding, however big we estimate it to be… it’s even bigger than that. The farthest objects that we can see may not be the farthest objects in general. Just because we cannot currently see beyond the objects 13.7 billion LY away doesn’t mean that there aren’t even more distant objects.
REFLECTION: I liked the article because, as stated above, it reiterates the concept that no matter how much we think we know about the universe, there is always more to be discovered. There is a lot about space that we will never ever be able to conceptualize and understand.