Dear Grandpa 
I'm
reading a book that says quantum physicists believe there are at least 7
newlydiscovered dimensions in addition to length, height, width, and time.
What are your thoughts? If
this is true, what in the world are these dimensions???
Ronnie
( Question is from Ronnie Sawyer  Age 18 )
Ronnie

The
word "dimension" has more than one meaning. When physicists talk of the four dimensions, those four have
some important characteristics.
1.
Dimensions all apply to every physical thing that exists.
2.
Dimensions can never be negative  only zero or positive.
3.
Dimensions must be "mutually orthogonal."
Here's
a way to see these characteristics:
Consider
a book. Let's say it's one inch
thick. Let's say it's 6 inches
tall. Let's say it's 5 inches wide.
Let's say it was published in 1940  and this particular copy was burned up in
1995.
Now
 the book existed for 55 years with its thickness, width and height.
But
now let's consider the same book  only with one of these dimensions zero.
Say the thickness is zero. Well
 the book does not exist. There is
no book.
Or
say the height is zero  Again, there is no book.
Or the width  No book.
Or
say the thickness, width and height are there, but the book exists for zero time
 Still  No book. It never
existed.
Can
you reasonably imagine a book that is minus 1 inch thick? No. Thickness is
positive only.
How
about minus 5 inches wide? No 
width can be positive only.
Minus
6 inches tall? No  height can be
positive only.
A
really small baby human may be only one foot long. A basketball player may be more than seven feet tall.
But nowhere is there a human that is minus seven feet tall  or minus any
height.
Length
is a better word for this than height. We
may turn the basketball player upside down and declare that his height measured
from his feet to his head is "minus seven feet," but he's still seven
feet long, and it's plus seven feet.
Also,
we might easily imagine a book that exists for zero time. It's
just a book that never was. But we
cannot reasonably imagine a book that exists for minus two years.
"Mutually
orthogonal" means that when one dimension is changed, the others are not
affected. They are independent.
Often we think of these as all at right angles to each other.
Up&Down is at a right angle to Left&Right and also at a right
angle to Forward&Back. Any one
of these three is at a right angle to the other two.
It's harder to see time this way  at right angles to the other three.
But one can see that if the book survives for two years or ten years, the
other three dimensions are unaffected by that difference.
Time
is a "dimension" in this special way.
If we could go "backwards" in time, then we could publish a
book in 2001  and take it with us to 1991, and we could say, "Here's a
book that is minus ten years old. Excuse
Grandpa, but "Poppycock."
We cannot move backwards in time, because having a negative time is just
like having a negative thickness or length. Something cannot cease to exist before it comes into
existence. A person cannot die before they are born. We can slow down  or speed up  but only zero to positive c
(The speed we have experimentally determined is the maximum.)
This constant, c, is not the speed of light, as often taught.
Light can travel at any speed up to c.
That's how lenses work; they slow the light down in an organized way. Responsible physicists keep their minds open, but we are
pretty sure that no actual thing can go faster than this.
As
mathematicians, we can define any number of other "dimensions."
We could plot the time it takes to boil water in a particular container
on a particular stove. We can call
the temperature one dimension  and time the other.
But temperature is not a dimension in the same way the "four"
are. Something could be reasonably
imagined to have zero temperature and still exist.
When temperature is raised, three of the dimensions increase with it, so
temperature is not "mutually orthogonal" to the others.
Temperature does meet the one requirement of never being negative, but
one requirement is not enough to be a "dimension."
(We talk about minus temperatures, but this is just a scale we use. The "absolute" temperature scale (Kelvin) tells us
how much heat is present, and we can't have a negative amount of heat.
On that scale, zero degrees  no heat  is roughly equivalent to 273
degrees centigrade.) Temperature is not a "dimension," in that we can't
use it to measure the "size" of some part of space or of an object in
space.
We
could also invent something with ten dimensions, calling color one, and
temperature one, and smoothness one, etc. These
are dimensions, but not by the responsible physicist's definition of a
"dimension of nature." There
were only three we recognized for a long time  and with Albert Einstein, we
came to recognize that time has the same qualities and acts the same way as the
other three.
There
is also a popular myth that someone or something can "come from another
dimension." We can't come from
length or width, etc. Again, this
is a completely different definition of dimension and has nothing to do with
spacetime.
If
anyone discovers that there is a fifth dimension  He or she will surely win a
Nobel prize. It will not be the
subject of the voodoo metaphysicist, but of real scientists.
I
was once involved in a research project wherein we contacted a man who was
arguing for a 9 dimensional universe. We,
the taxpayers paid this quack more than a hundred thousand dollars.
He was making claims with absolutely nothing to back them up.
He was pretending to be a physicist with an interest in his country, but
he was actually just a thief.
Grandpa
sometimes thinks that it is unfortunate that a less sophisticated thief, who
takes an object, goes to jail, while these more sophisticated thieves always go
free, even while we are fully aware that they have taken much more.

Grandpa
Note:
Another student asked if "spirit" is a dimension.
You may figure out from the above that spirit may be regarded as a
dimension, but it is not a dimension in the same sense that length is  or the
others of the four.
Note:
Remember  no "thing" can exist unless it has measurements of
nonzero for all four of the dimensions. This
refers to physical things. We may
regard Love or Enthusiasm or Trust to exist, and these do not have widths,
lengths, thicknesses. These are not
"things" in the physical sense. They
are more like "ideas," or concepts of the mind.
So what about the dimensions themselves? Are they "things", or are they "ideas"?
Think about it. Does length have width and thickness? No. Length is
the name of one of the dimensions, but it does not have dimensions itself.
Length is an idea, not a thing. A
thing must have length, but length is not a thing itself.
That makes it clear that someone cannot "come from another
dimension." One cannot come
from a place that does not exist as a physical place.
People can't "move" from one dimension to another. Dimensions are not places.
People and other things are not in some dimension; they have nonzero
positive values for each dimension. Dimensions
do not weigh anything. They are not
physical things.