Answer 1:
This is a good question. This topic is hugely
important in science and the philosophy of
science, and it was the basis of a scientific
revolution. I will give some background on the
topic before summarizing some observations that
strongly support the theory that the earth orbits
the sun. Most of the information that I am
presenting below is from the NASA website click
here to watch.
There has been debate since the time of the
ancient Greeks whether the earth orbits the sun or
the other way around. Aristotle, a prominent Greek
philosopher, hypothesized that the earth is the
center of the universe, and that all other
celestial bodies rotate around it. This was based
on observations such as:
1) an observer cannot feel the earth move,
2) there was no perpetual wind on the surface of
the earth. The geocentric (earth in the center)
view of the universe prevailed for over a millennium.
In the 1500s a Polish scholar, Nicolaus
Copernicus, proposed a heliocentric model: that
the sun was the center of the universe. Keep in
mind that we now know that the sun is not actually
the center of the universe. For a while, the
church oppressed Copernicus’ hypothesis because it
contradicted certain dogmatic beliefs.
After Copernicus died, his hypothesis began to
gather support, and strong scientific work by
Johannes Kepler and Galileo provided evidence that
finally dispelled the geocentric model (at least
among scientists). Kepler formulated a
mathematical model for how earth and the other
planets of our solar system orbit the sun.
Galileo used the first high-powered telescope
to observe planetary motion. One of his most
important observations was that there were several
small bodies that orbit the planet Jupiter. This
was a very important observation that ruled out
the idea that all bodies orbit earth. Another one
of Galileo’s observations was that Venus displayed
a full range of phases (like the shadows on our
moon), which can only be explained if Venus and
earth both revolve around the sun on different
orbits.
Isaac Newton’s theory of universal gravitation
tied everything together. It provided a strong
theoretical basis for why the earth and other
planets orbit around the sun.
So what about Aristotle’s observations? They are
accurate, right? We can’t feel the earth hurtling
through space. Here’s a thought exercise:
The earth revolves about its axis about once
every 24 hours. This is the angular velocity of
the earth about its rotational axis. The radius of
the earth at the equator is about 3960 miles. The
magnitude of linear velocity of a rotating point
is equal to the angular velocity (in radians/time)
multiplied by the radius to the point. Calculating
the velocity of the surface of the earth at the
equator relative to the center of the earth:
(2π radians/24 hours) x 3960 miles = ~ 1037 miles/hour
That’s pretty fast. Why don’t we feel it? It is
because speed is always measured relative to some
reference frame. The surface of the earth is the
reference frame relative to which we sense
“speed”.
The bottom line here is that the model of the
earth and other planets revolving around the sun
fits our observations. The model that the earth is
the center of the universe is inconsistent with
our observations– they do not fit. A crucial
characteristic of science is that hypotheses (like
the geocentric model) must be refutable.
That is, there must be ways to test if they
are wrong. If a hypothesis is proven wrong by our
observations, we must be prepared to change it or
discard it. Keep in mind that this is how science
works, and religious beliefs do not evolve in the
same way as scientific beliefs. Religious and
scientific beliefs are not really comparable. When
religious beliefs are considered in a scientific
way, they are easily refuted. This doesn’t mean
that religion is bad, it is just fundamentally
different from science.
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