Is the universe getting bigger or smaller?

After the discovery of galaxies beyond the Milky Way, Edwin Hubble measured the distances to hundreds of other galaxies, his data reveals how the universe is changing with time and also it gives some clues of the formation of universe.

If the universe is expanding, it must be once much smaller than it is now. This realization led to the Big Bang theory: the thought that the universe began as something incredibly small, then expanded incredibly quickly. We can see the "afterglow" of the Big Bang even today, within the cosmic microwave background – a continuing stream of radio waves, coming from all directions within the sky.

For a universe containing matter and light, the solution to the present question depends on what proportion stuff there is. More stuff means more gravity, which pulls everything back together and slows the expansion.

As long because the amount of stuff doesn't re-evaluate a critical threshold, the universe will still expand forever, and eventually suffer heat death, freezing out.

But if there is an excessive amount of stuff, the expansion of the universe will hamper and stop. Then the universe will begin to contract. A contracting universe will shrink smaller and smaller, getting hotter and denser, eventually ending during a fabulously compact inferno, a kind of reverse explosion referred to as the Big Crunch.

In order to know whether the universe is expanding or contracting we should go with the phenomenon called as redshift and blueshift. Redshift occurs when the light source is moving away from the observer or when the space between the observer and the source is stretched. If we apply this theory to stars and galaxies, when astronomers see redshift in the light from a galaxy they know that the galaxy is moving away from the Earth. As the distance increases they observe a redshift and as the distance decreases they observe a blueshift.

If a light source moves away from an observer according to the visible range of electromagnetic spectrum will be redshifted. If the source moves toward the observer it will be blueshifted. This phenomenon can occur with other types of waves too. It is called the Doppler Effect. It describes the increment and the decrement in the frequency of sound, light or the other waves, as the source and the observer move toward or away from each other. This causes the changes of pitch noticeable in a passing siren. An analogy to redshift is the noise of a siren of an ambulance. As it passes you the sound waves shift towards a lower pitch. Though in redshift there it involves light instead of sound a similar principle operates in both situations.

Edwin Hubble collected data of the distances to galaxies with other astronomers’ measurements and introduced a relationship, now we called, “Hubble’s Law”, the farther away a galaxy is the faster it is moving away from us. Since almost every galaxy in the universe has a red shift, almost every galaxy moving away from us. That shows our universe is expanding.

In 1998, two competing teams of astrophysicists made an astonishing announcement: the expansion of the universe is speeding up.

Normal matter and energy cannot make the universe behave this manner. This was the primary evidence of a fundamentally new quite energy, dubbed "dark energy", which did not behave like anything within the cosmos.

Dark energy pulls the universe apart. Roughly 70% of the energy within the universe is dark energy, which number is growing a day.

The existence of dark energy means the quantity of stuff within the universe does not get to work out its ultimate fate.

Instead, dark energy controls the cosmos, accelerating the expansion of the universe for all time. This makes the Big Crunch much less likely.

Article by - Kulathi Nishshankage

Graphics by Deshan Rathnayake

J'pura Astronomy Club

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