Astronomy Wonder Project

How was the concept of gravity realized, and how is it measured?

Gravity is defined to be the force by which a planet or other body draws objects towards its center. The same force that allows for planets in our solar system to orbit the sun, or what makes things fall on the ground here on Earth.

How was it discovered?

In the 1600s, the concept of gravity was realized when Isaac Newton witness a falling apple from a tree while he thought about the forces of nature. He developed the theory that defined gravity as a universal force acting on all matter, the farther apart two particles are and the less mass they have, the less gravitational force they posses. The theory was left unchallenged for 3 centuries, until in the 1900s Albert Einsten extended Newton’s theory with his general theory of relativity. He argued that gravity was more than just a force; it was a curve in the fourth dimension of space and time. Given enough mass, an object can cause a straight beam of light to curve, this effect is what astronomers call gravitational lensing, which was one of the methods leading to the discovery of black holes.

Here is a video explaining more about Einsten’s theory of Relativity >>

How can gravity be measured?

It was said that the greater the mass and the closer together, the more stronger the gravitational pull, so with that how exactly were they able to determine the strength of gravity on Earth? It was assumed that the acceleration of a body due to gravity is a constant 9.81 meters per second squared, by every square meter gained toward the planet’s centre, the faster the object goes down. However the assumption would be considered true only if the planet was completely smooth and contains equal amounts of elements and minerals. Earths consists of mountains, caves, difference in terrain, oceans, valleys, etc, all containing different amounts of mass which influences the gravitational pull in different regions.

One of the way to find where on Earth is gravity the strongest or weakest, in 2002 NASA and German Aerospace Centre launch a joint mission names GRACE (short for Gravity Recovery and Climate Experiment), sending 2 satellites into the same orbit around Earth. One about 220 kilometers (137 miles) in front of the other at an altitude of 460 kilometers (286 miles) above the Earth’s surface. As the leading satellite passes over a stronger area of gravity, it would detect the gravitational pull and increase in speed slightly, thus decreasing distance from the tailing satellite, and the opposite happens when the lead satellite passes over a weaker gravitational pull, having distance increase between the satellites. The changes in distance between the satellites are very small– about one-tenth the width of a human hair — that they are undetectable by the human eye. GRACE measures these changes by generating pulses of microwave energy — a highly energetic form of electromagnetic radiation — that bounce back and forth between the two satellites. The distance between the satellites is determined by the time a microwave pulse takes to travel from one satellite to the other and back. Along with this, GRACE maps the entire gravitational field of the planet every 30 days, and with changes in gravity happening over time reveals detail about polar ice, sea level, ocean currents, Earth’s water cycle and the interior structure of the Earth.

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Overall, one of the studies of gravity involves a branch of Quantum Theory, which is known as quantum gravity, in which scientists attempt to generally relate to each other. Quantum Theory refers to how does the universe work in the smallest level (subatomic) and it helps scientists develop standard models for particle physics which details more about the inner workings of the universe. However quantum gravity has one exception – it doesn’t explain much about gravity.

Both theories of Quantum Theory and relativity do explain most about the observable universe (the “horizon” of  the universe we are able to see from Earth), and contradict each other like in the study of black holes. Not unexpected, numerous scientist do continuous work toward a unified theory. Whatever theories are adopted, it is difficult to overstate the importance of gravity, it is the glue that holds the cosmos together, even if its leaves unanswered questions about the universe.

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Here is a video demonstrating gravity>>

Resources

Image – Gravity

Image – Gravity Map

What is Gravity – Howstuffworks.com

What is Gravity – spaceplace.nasa.gov

GRACE – NASA

Gene Drive Podcast – Science 10

Podcast Notes

What type of gene mutations did scientists edit?

• A gene mutation responsible for a heart disease in humans.
• It involves the gene that develops the heart muscle.

What is a germ line mutation? How many do humans have?

• Germ line mutations are inherited mutations from one generation that have been past to the next generation.
• There are various different germ lines (thousands).
• Because like in DNA between humans, 99.9% of our DNA are similar with 0.1% being the component that makes us unique from each other.

Why do scientists perform gene therapy at the embryotic stage?

“The embryotic stage is the earliest stage to perform the gene therapy before the time of fertilization. Scientists were tasks to access and change the mutation, so they work at this stage because basically when the child is born, the mutation has already been incorporated in the development, so changing every effected cell (which are billions) back to normal is impossible.”

Do you agree with the practice of humans altering genomes of species? Why or why not?

“Well generally, I wouldn’t go for it because DNA is coded instructions for the development of organisms, so it seems like a delicate process to alter and it shouldn’t be messed with. However, of course the purpose of gene therapy research is to find a safe treatment of genetic diseases, so I would only agree to that.”

DNA Model

DNA – aka deoxyribonucleic acid is a chain molecule made up of a sequence of molecular components that exists in nearly all organisms. The components are known as chemical bases which act as a code of instructions for making an entire living being to develop and survive. DNA is stored in the nucleus of every cell tightly coiled into 23 pairs of chromosomes (except blood cells, since they lose their DNA as the mature). We inherit 23 chromosomes from our parents.

DNA is often known to be in a form of a double helix made of two strands of sugar and phosphate linked together by a pair of bases, and these bases form long sequence called genes that are coded instructions to build proteins. When a cell needs to duplicate or make a protein, the helix splits itself into two halves so that a copy of the gene can be made. The bases are Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) – they always form with the same pairs (A-T, G – C) and these pair make up the entire sequence of DNA.

Since genes code the molecules that are essential for life, majority of genes are the same in everyone. However only about 1% have different variations – known as alleles which give unique physical traits like hair or eye color. They could result in more problematic conditions, like hemophilia or cystic fibrosis because alleles come in pairs, one can override the other so that the trail remain hidden.