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Redshift: Why Galaxies Run Away!

  • Writer: stembeyondseas
    stembeyondseas
  • Jul 24
  • 4 min read


Waves

A wave is a disturbance travelling through space-time. They transfer energy from one point to another, without any permanent displacement in space-time. There are waves all around us: from sound waves, to light waves, to water waves. These waves can be arranged in order of increasing or decreasing frequency, this is known as the electromagnetic spectrum.


The Electromagnetic Spectrum

The electromagnetic spectrum is the entire continuum of electromagnetic radiation ordered by frequency, wavelength, and energy. The spectrum is arranged in order of increasing frequency and decreasing wavelength. The order is shown as: radio waves, microwaves, infrared, visible light, UV rays, x-rays, and gamma rays.


The Spectrum of Visible Light

The spectrum of visible light consists of white light arranged in the order of increasing or decreasing frequency. In the order of increasing frequency and decreasing wavelength the spectrum of visible light is as follows: red, orange, yellow, green, blue, indigo, and violet. The most commonly used acronym for this spectrum is ROYGBIV. It is in this arrangement that the spectrum of visible light fits into the wider spectrum of electromagnetic waves.


The Doppler Effect

Have you ever wondered why the sirens of a moving ambulance or police car sound the way they do?

Imagine yourself walking along the side of a road, maybe you're on your way to school or work. All of a sudden a car comes whizzing past you. Why does the blaring car horn sound louder when the car is driving past you as opposed to when it's driving away? As the car moves past you the sound waves that the car emits get all squished together, so the waves have a shorter wavelength and a higher frequency. Thus, this increases the pitch of the sound and as the car drives past you the sound waves it emits spread out. The wavelength increases and the frequency decreases, so the pitch drops.


What is Red Shifting?

Here on earth we get our light from the sun. This light then travels through empty space and reaches us through radiation. When this light enters the earth's atmosphere and is absorbed by various compounds that make up our atmosphere, the rest of the light is transmitted towards us. Since these numerous substances absorb different wavelengths of light, the spectrum of visible light is left with a few black patches due to the absence of light. We therefore call this patchy spectrum the absorption spectra.

When we compare the absorption spectrum of light emitted by the sun to the absorption spectra of light emitted by distant galaxies, we can observe that the patches are shifted towards the red light. This is a result of the doppler effect. As these distant galaxies move away from us the wavelengths of light they emit spread out and the black patches shift towards the red light of the spectra. We then say that this light is red shifted.


The Big Bang Theory

Because of red shifting we can deduce that these distant galaxies are moving away from us, not because the galaxies themselves are moving, but because the empty space between these galaxies is shifting. Space is expanding, so that means the universe must have been much smaller before its expansion! If we go back in time we can hypothesize that the universe must have been incredibly compact years before.

The universe once existed in a hot dense state. This included a pool of: protons, neutrons, electrons, and photons. They were constantly absorbing and remitting energy, until about 380,000 years later when it finally cooled to a nice 2700°C. At 2700°C electrons began to orbit hydrogen, helium, and lithium atoms, while the photons began to travel through free space. Proof of this include:

  • The abundance of hydrogen, helium, and lithium in our universe

  • Red shifted light from distant galaxies

  • Cosmic microwave background radiation


Cosmic Microwave Background Radiation

The heat from the early universe was emitted as infrared radiation, but since the expansion of the universe these wavelengths have been stretched out all the way to microwave wavelengths on the electromagnetic spectrum.

Cosmic microwave background radiation was first discovered in 1965 by Arno Penzias and Robert Wilson. They weren't even trying to prove the Big Bang theory. Instead, they were actually working at Bell Laboratories in New Jersey, testing a massive microwave antenna called the Holmdel Horn Antenna. It was designed for satellite communication, but no matter where they pointed it, they detected a faint microwave noise coming from every direction in the sky. That "noise" turned out to be the leftover radiation from the early universe, which turned out to be the cosmic microwave background.

The first detailed image of the CMB was taken all the way in 1992 by NASA'S COBE satellite (Cosmic Background Explorer). COBE produced the first map showing tiny temperature fluctuations in the CMB. Those small variations were crucial because they showed the seeds of future galaxy formation.

The Big Bang theory, while widely accepted, has faced a number of challenges over the years, including the flatness problem, the horizon problem, and the monopole problem. Proposed solutions such as cosmic inflation, supercooling, and other mechanisms offer plausible explanations for these issues, but they still lack definitive experimental proof. As a result, the Big Bang remains a theory, a well-supported framework for understanding the origin and evolution of the universe rather than a law. Its explanatory power continues to grow with new observations, yet the door remains open for refinements or alternative models in the future.


Writer:Mohammed Ayotunde

Editor:Harley Cruz


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