Harden Elkington
One thing was relatively certain about the universe’s growth in the early 1990s. It may have enough energy density to halt its expansion and collapse, or it may have so little energy density that it would never stop expanding, but gravity would inevitably slow the expansion as time passed.
The universe is composed of matter, and gravity’s attractive power draws all things together.
Eventually, the universe will stop expanding and recollapse in a big crunch. Or it would be, if not for dark energy.
Then came 1998, and the Hubble Space Telescope observations of extremely distant supernovae that revealed that the universe was expanding at a slower rate in the past.
As a result, rather than slowing down as had been commonly assumed due to gravity, the universe is speeding up. No one anticipated it; no one knew how to explain it.
But Something was making the universe accelerate.
It didn’t take long to find where the missing energy was coming from dark energy, an unknown form of energy inherent to space itself.
And while we don’t know what dark energy is or why it exists, we know that it’s causing the expansion of our universe to speed up.
Finally, three distinct types of theories were developed.
It could have been the consequence of a long-abandoned version of Einstein’s gravity theory, which included what was known as a “cosmological constant.”
Perhaps there was some odd type of energy fluid that filled space.
There’s still no agreement on whether or not there’s anything wrong with Einstein’s general theory of relativity, but maybe a different idea would incorporate some sort of field that generates cosmic acceleration.
Theories have yet to determine the true explanation, but they have given it a name. It is known as dark energy.
What is dark matter?
The existence of dark matter is inferred from gravitational effects that can be seen on the scale of our own galaxy.
For example, spiral galaxies rotate around their galactic centers so quickly that they should fly apart unless some type of dark matter exists to keep them together.
There are many different theories about what dark matter might consist of, but so far there has been no conclusive observational evidence.
As with dark energy, it is thought that dark matter may manifest itself as a new type of elementary particle, one that interacts very weakly with our known universe.
So far, astronomers have not been able to detect dark matter directly – however, several lines of evidence suggest that it is there.
One way to detect dark matter would be through its effect on other objects within the Milky Way galaxy.
The motion of a large body, such as a star or a galaxy, produces what is known as a gravitational lensing effect.
When light from an object behind the dark matter passes by the large body on its way towards Earth, it takes on the shape of a cross that astronomers refer to as an Einstein Cross.
Several such multiple images of more distant galaxies have been found, suggesting that there is more gravitational influence acting upon the galaxy than can be explained by visible matter.
What is dark energy?
Scientists have known for a long time that the universe is expanding – initially expected to slow down over time due to gravity, it is now understood that the expansion of the universe has been accelerating.
This acceleration can be attributed to a mysterious form of energy, called dark energy, which makes up roughly 68% of the existing energy content in our present universe.
Though we don’t know what dark energy is, we do know that it produces a repulsive gravitational effect and has been causing the accelerated expansion of our universe.
Dark matter is thought to exist because galaxies spin faster than the speed at which gravity can pull their contents together.
Through observations and studies of hundreds of thousands of galaxies, we’ve concluded that there must be some invisible and unknown type of matter that generates sufficient gravitational force to hold the galaxy together.
Studies have shown that dark matter does not interact with “normal” baryonic matter (matter composed of protons, neutrons, and electrons) – but it does seem to interact with itself.
- Related post: What would happen if the earth stops spinning?
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What are the differences between dark matter and dark energy?
The main difference between dark matter and dark energy is what each one consists of.
Scientists believe that dark matter consists of material not detectable by our current instruments while they believe that dark energy is some type of energy field that exists throughout space.
Scientists believe dark matter is composed of material not detectable by our current instruments, while they believe dark energy is some type of energy field that exists throughout space.
Scientists believe that dark matter exists because galaxies spin faster than the speed at which gravity can pull their contents together.
Through observations and studies of hundreds of thousands of galaxies, we’ve concluded that there must be some invisible and unknown type of matter that generates sufficient gravitational force to hold the galaxy together.
Studies have shown that dark matter does not interact with “normal” baryonic matter (matter composed of protons, neutrons, and electrons) – but it does seem to interact with itself.
Scientists have known for a long time that the universe is expanding – initially expected to slow down over time due to gravity, it is now understood that the expansion of the universe has been accelerating.
This acceleration can be attributed to a mysterious form of energy, called dark energy, which makes up roughly 68% of the existing energy content in our present universe.
Though we don’t know what dark energy is, we do know that it produces a repulsive gravitational effect and has been causing the accelerated expansion of our universe.
Conclusion
In a nutshell, dark energy is something that exists throughout space and can be attributed to the accelerated expansion of our universe.
Dark matter is considered to exist because galaxies spin faster than the speed at which gravity can pull their contents together.
Scientists believe this invisible and unknown type of matter generates sufficient gravitational force to hold a galaxy together.
As for what each one consists of: dark matter is believed to be composed of material not detectable by our current instruments while it’s believed that dark energy is some type of energy field that exists throughout space.
Research into dark matter and dark energy will continue, with the hope that upcoming technologies will bring us closer to understanding what each one actually consists of
