People tend to rely on their everyday experience, as revealed by
their senses, to shape their impression of what is ``typical.''
- Personal scientific inferences can be highly skewed by
perspective (for example, Astronomy prior to 1543).
Physical Conditions on Earth are Unrepresentative of the Universe
- We live in a place where matter is relatively densely packed.
- A cubic centimeter of air contains about 1019
- In intergalactic space there is typically one atom
per volume the size of a football stadium.
- We live right next to a star.
- Here on Earth the typical temperature is 300 degrees
above the absolute
zero of temperature.
- In intergalactic space the temperature is about 3
degrees above absolute zero.
Human Senses -- particularly vision -- provide an extremely limited perspective
- The "light" which our eyes can detect is a tiny fraction
of the entire electromagnetic spectrum.
- Radio, Infrared,
Ultraviolet, X-ray, and Gamma-ray
light fill the universe, but unlike visible light cannot be detected by our eyes.
- Observations at these other wavelengths, made possible
by advances in detector technology, reveal unique
undetectable in visible light.
- Consider these views of our Milky Way galaxy using
- Modern astronomy exploits the ability to observe
the universe throughout the electromagnetic spectrum, taking
us far beyond the limitation of human senses.
A human's perspective on time is similarly narrow
- The brief span of a human
lifetime provides only a snapshot observation of the Universe.
- Most cosmic systems do not change appreciably over
- A human lifetime is to the 13.7 billion year age of the
Universe as a fraction of a second is to one year.
- The entire span of recorded history relative to the age
of the Universe amounts to
less than one minute compared with an entire year.
- Astronomers must reconstruct the workings and evolution
of the universe from this brief snapshot.
- The challenge is similar to trying to reconstruct
the workings of politics and human relationships based
on a one-second glimpse of events on Earth.
- Astronomers have two primary tools at their disposal to overcome this disadvantage.
- Astronomers can
literally look back
in time and see the Universe as it was long ago because
light takes time to get here from distant objects.
- Astronomers can use computations to simulate the passage of immense time. Modern computers permit astronomers to examine
the workings of some aspects of the Universe over periods
amounting to billions of years. Examples:
Limited comprehension of large numbers
- We can visualize quantities of a dozen or a few hundred
but what is the real difference between a billion and a trillion?
- Rescaling quantities can help make numbers meaningful and thus help overcome a biased view.
- Examples include expressing...
- stellar masses in terms of the mass of our Sun instead of using grams.
- distances in the Solar System using "Astronomical Units" (the average Earth-Sun
distance = 1 A.U.).
- sizes of Solar System objects in terms of the size of the Earth.
- Scientific notation
can make astronomical quantities manageable.
- Although scientific notation makes the numbers manageable, it still does not give them meaning.