Hubble's Law of Cosmic Expansion. Is the Universe Expanding?
In 1929, astronomer Edwin Hubble used the 100-inch Hooker Telescope at Mount Wilson Observatory to make an astonishing discovery. He noticed that several Cepheid variable stars were at different distances from Earth, and each was dimmer than the last. This indicated that the stars were physically moving away from one another, suggesting that the entire universe was expanding! This revolutionary finding was later formalized by what’s known as Hubble’s Law of Cosmic Expansion, which states that the more distant a galaxy is from Earth, the faster it appears to be moving away from us on the other side of the observable universe.
What is Hubble’s Law
Edwin Hubble observed a curious effect and gave it a name. He realized that as space telescopes get more powerful, they’re able to see even farther into space. Objects that are very far away can be studied in much greater detail, too, because there’s less distortion from Earth’s atmosphere. That led him to his discovery: The universe is expanding and objects are getting farther apart from each other all of time. No matter where you look in space, galaxies seem to be flying away from one another faster than speed-of-light speeds (186,000 miles per second). They’re moving so fast in fact that light coming from them appears redder than it otherwise would because of their speed—the Doppler Effect.
How do scientists know this is happening?
Scientists have learned that as time goes on, galaxies are getting farther apart. This is because everything in space appears to be moving away from everything else. Scientists know that each galaxy is moving at a different speed and going in a different direction. We know all these things because astronomers can see light coming from distant objects. The more distant an object, the longer it takes for its light to reach us; therefore, we are observing objects at an earlier point in time than we might think if we didn't take into account how far away they actually are.
What happens if the universe expands faster than light speed?
While it sounds like science fiction, there is a possibility that if our universe expands faster than light speed, there is nothing to slow it down. If that were to happen, we could never receive information from other galaxies because they will be moving away too fast for us to ever detect them. That would make studying and understanding our universe impossible because we would always be left behind. We would not even be able to see what other galaxies look like today as they will all have moved so far away from us in such a short time that they will appear much smaller than they really are and therefore undetectable. Our view into our universe would then be limited only to what is around us today without ever being able get a glimpse at what is beyond.
What happens if the universe slows down and stops expanding completely?
It would either collapse in on itself or rip apart, depending on how its mass was distributed. In general, gravity is an attractive force and tends to pull matter together. The universe could also expand forever but just at a slower rate. So far there's no evidence that expansion is slowing down, but we don't have telescopes that can detect expansion over billions of years (it takes light billions of years to reach us). If a time machine was invented it could travel back billions of years in time and see if there were any changes in its expansion rate from when we're alive.
The ultimate fate of our universe
Many theories exist, but they all come back to a central question: Will our universe continue to expand or will it eventually collapse in on itself? One thing is for sure: we’re not done yet. It will be billions of years before astronomers can say with any certainty what happened and what will happen in our ever-changing universe. Although some astronomers posit that our universe may indeed shrink at some point, most agree that many billions or trillions of years from now, when every star has finally burned out, gravity won’t be strong enough to reverse universal expansion—the rate at which galaxies move away from each other—and that the universe as we know it today will end long before then.