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myNotes
Although black holes
are real, they are
invisible. In this image,
an illustrator imagines
what a black hole
might look like.
No one has ever seen a black hole
Is Bigfoot REAL? 15 (they’re invisible!). No one has ever been
12 The truth is, no one knows for sure, inside one. But we can form theories about
although many people have strong opinions their existence because of careful, repeatable
on the matter. We can only be absolutely observations that have been made. As we
certain there is such a creature as bigfoot learn more about physics, we might
when we have found one. someday adjust our understanding and
13 Otherwise, bigfoot remains a theoretical definition of black holes. But no one calls
possibility. A theory is an explanation of scientists crazy for believing such a thing
something based on observations, exists because there is enough evidence to
experiments, and reasoning. When formed make it a reasonable thing to believe in.
with care, theories are scientifically valid— 16 Scientists ask questions, make
even if they are not proven, and even when observations, come up with smart guesses,
they apply to things we haven’t seen. devise experiments to test them, and
14 Take black holes, for example. These are consider the results thoughtfully. And
spots in space, big and small, where matter that’s exactly what you can do when it
has been compressed (this can happen when comes to bigfoot. There’s nothing wrong
a star dies). The compression of matter with a healthy dose of skepticism. That’s
makes for an incredibly strong gravitational how scientists get smarter. And open
pull—a pull so strong nothing can escape it, minds are the only ones that can learn
not even light. new things.
theoretical Something that is theoretical is based on a guess rather than truth.
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