Ask A Scientist General Science Archive

name         Jack R.
status       educator
age          30s

Question -   I am teaching 6th graders in Santa Clara, Ca. I taught my
students about facts and theories. I said it is a theory that the center
of the earth is liquid because we have not been able to dig down that
deep and must merely speculate with mathematical formulas. I also said
the sun being classified as a star would technically be a theory also
since we have not been able to get close enough to stars to find out if
they are made of the same stuff as the sun.

Am I correct? One of my coworkers disagrees saying both are facts. Could
you recommend a web site or book which explains the differences between
facts and theories for 6th graders?
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Hi, Jack !!!

I can only partially answer your question.
In a way, it is really NOT necessary to deep
into stars to know what are they made of.
As you know, it is possible by analysis of
electromagnetic waves to know the compo-
sition of a star. And, if it is so, you can compare
our sun to other stars and check that type of
gas composition they are surrounded by.
Besides that, you can also measure the superficial
temperature, among other properties. The
Hertzprung-Russel diagram indicates the
position of our sun in the universal scale and
from this point on, it is possible to predict
the life-time of our sun.

If the center of our planet is liquid or not can
be confirmed in what volcanoes expel.It is
a liquid lava, so that the center of the Earth
must be fulfilled with a viscous liquid, right ?

Surely theories have their origin in some facts,
like for instance, the "big bang". The astronomer Hubble
could confirm that the light of star shift to red which is
an indication that the universe expands. Einstein
- in his mathematical calculations - could also predict
this fact ( lets forget about the cosmological constant ).
In this way, you have to admit that the whole universe
came from ... a point. And what to say about black holes ??
This is a theory, and what  an
amazing theory !!! So, that is it : an observation asks
for theories, what in turn, calls for another type of
observation. And so the snow ball gets big and bigger...

Take a look on this site :

http://imagine.gsfc.nasa.gov/docs/ask_astro/ask_an_astronomer.html

This address may be extremely useful to you !!

Alcir Grohmann
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I think that your criterion for a scientific "fact" is far too restrictive.
The term "fact" should be banished from the scientific lexicon. It implies
something that is not refutable which is true (whatever that means) under
all conditions. I cannot think of a any case where that happens. A better
term is "observation" or "experimental data".

Seldom do we directly experience a scientific observation. Almost always we
use some sort of instrument that measures something and provides us with
some sort of "signal" be it visual, audible, electronic, and so on. Your
definition would exclude almost all scientific measurements. For example,
your definition would exclude atoms and molecules, viruses, electrical
charge, x-rays, and so on. We don't have to experience rattlesnake venom to
assert confidently that it is toxic if injected.

Scientific observations / experimental data are what result from some
qualitative or quantitative measurement. The observations may involve simple
or complicated intervening instrumentation. Four attributes of scientific
data are: ACCURACY (how close the measurement is to the "true" value, which
more often than not is unknown), PRECISION (how many significant figures
does the measurement yield, an observation can have high precision and poor
accuracy), REPRODUCIBILITY (does the experiment yield the same result if
repeated, either by the same observer, or more stringently, by other
observers using the same or different techniques). RELIABILITY (how well do
the observations withstand the prolonged study) is a mixture of the other
three properties. You can teach very young children to make observations;
they are able to grasp this concept easily, I have found.

A scientific LAW is the statement of the results of many experimental
measurements that can be related in such a way as to give the same
inter-relation. The ideal gas law, inverse square law of gravity, ohm's law
are examples -- there are many, many more.

I find your characterization "merely speculate with mathematical formulas"
disturbing. It seems to imply that mathematical expressions are some sort
of "hand waving, smoke and mirrors".
Nothing could be further from the truth. Your characterization makes me
suspect that you don't have much faith in the concept of scientific theory,
because they are very often mathematical. A scientific THEORY makes
some statements (assumptions, hypotheses) from which a large number of
conclusions can/must be consequences. Newtonian mechanics, quantum
mechanics, relativistic mechanics. Scientific theory is the most powerful of
all scientific statements because it must not only state the result of prior
experimental observations, but must predict, in advance, the result of
experiments that have not yet been done. A key property, the sine qua non,
is REFUTABILITY. A scientific theory must be able to be shown to be false,
or subject to change in the light of new experimental data. That is the very
key to its power -- it can be disproved! Statements that do not have this
property are DOGMA -- which is a "take it or leave it" statement.

Vince Calder
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A theory is an idea that is consistent with all known, relevant facts.
A fact is an idea that has been proven true.  Generally, this means
that other theories have been proven false, and that new knowledge will
not change the state of the proof -- a very strong statement, given
that we do not know what the new knowledge might be.

It is not necessary actually to touch something to prove that an idea
about it is true.  In the case of stars, getting close would not help
all that much in any case, because even if you had some star stuff in
your hand, the tests you'd do to find out what it's made of would be
pretty much the same as what you would have done through a telescope.

The center of the earth is generally thought to be solid iron with some
impurities, surrounded by liquid iron with lots of impurities.  I have
seen some very convincing evidence favoring this theory.  I do not know
whether or not it's a fact, however, because I do not have a thorough
enough understanding of the fields of study that bear on the problem.
I have to take somebody's word for this.  So what is the state of my
knowledge about the core?  It depends on whether or not I find the
experts credible, does not it?

Tim Mooney
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You have ventured into the realm of epistemology somewhat.  Theories are
those explanations for events in nature that will, after experimentation, be
discarded, changed or shown to be accurate...but NEVER proved as fact.  Then
there are those events in nature which we would accept through our senses as
REAL.  The snow on the ground or the hardness of a rock.  These are in my
opinion "facts" of nature by our definition through our sense experiences.
Is it possible that a "fact" be proven wrong and if so was the fact not
REALY a fact then?

Well, all this philosophizing aside, let me try and put this in perspective.


1. science gathers its knowledge and concludes based on inductive
reasoning...levels of probability, the null hypothesis and such, and
therefore NEVER really "Proves" any theory to be immutable (a fact so to
say).  Science only gives us a rational way of expecting to a certain level
of certainty that something is what a certain theory says it is.
2. Facts are few and always suspect to change.

In this light, (no pun intended).  The sun is, by definition, a star.  A
star is that glowing celestial body that derives its energy from its great
mass initiating and maintaining nuclear fusion.  We derive this from
numerous scientific experiments that show that the sun, although closer is
composed of the same elements as stars of its class.  I, as a scientist,
base this on the following which some would take as facts...I take them as
statistical reference points...  they are: the suns diffraction analyses,
luminosity, electromagnetic emissions, magnetic fields, mass etc.  We also
have the some information on the celestial bodies far from us which we also
classify as stars based on the same properties.  We have seen and recorded
100's of thousands of stars in the universe like our sun which has a certain
measured luminosity, temperature, mass, magnetic field etc.  So the sun I
would say is certainly a star because it fits all theories belonging to
stardom and all the properties that stardom contains.

To say we have to be at the center of the Earth to confirm our theory into
fact on the iron core and its temperature gives greater weight to our senses
that interpret local events.  The problem then is that we are left with the
question of when we become convinced of something being a genuine fact and
to allow closeness and direct senses to take first place is NOT always the
most dependable thing.  If I "see" a star...that star, I might say, exists,
but we know that the light might have long since left a start long since
dead which is now just reaching me.  So scientists depend on numerous
approaches to convince themselves that something is accepted as nearly
bulletproof...The center of the earth as being made of molten iron is
deduced by numerous measurements that can, as of now, only be explained by
its given composition...The earth's magnetic field, radioisotope analysis of
the interior, deep core drilling, seismic studies etc.  This is much more
theoretical though because we have not gathered as much "hard evidence"...
"facts"

Nothing is easy!

Peter Faletra Ph.D.
Assistant Director
Office of Science
Department of Energy
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