Dear Grandpa -

I'm reading a book that says quantum physicists believe there are at least 7 newly-discovered 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 space-time.

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 non-zero 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 non-zero positive values for each dimension.  Dimensions do not weigh anything.  They are not physical things.