String theory is a theory of everything. It attempts to merge all the dimensions and particles into one universal theory.

String theory postulates that everything in the universe is composed of tiny strings of energy. These strings vibrate in a variety of ways, producing the different forces and particles we observe in the universe.

There are five known fundamental forces in the universe: strong force, weak force, electromagnetic force, gravity, and string force. Due to this, some theorists have postulated that there are more than four dimensions.

Since strings require space to vibrate, adding more dimensions would allow for more spatial room for the strings to move around in. This would explain why we can’t detect more than four dimensions using current scientific methods.

This article will discuss how many dimensions there are, how to identify them, and how we can use them to our advantage.

## XX

The letter “x” is the only letter that does not appear in any string of four lowercase letters. There are no strings of four lowercase letters that have the letter “x” in them.

There are, however, strings of four lowercase letters that have two Xs in them. For example, the strings “xx” or “xxx” contain two Xs. There are also strings of four lowercase letters with three Xs in them, like “xxxx” or “xxxi.”

Interestingly, there are no strings of four lowercase letters with five Xs in them. You can try to find a string of four lowercase letters with five Xs in them, but you will not find any. This is because there are no strings of four lowercase letters with five Xs in them.

The same goes for six and seven Xs in a string of four lowercase letters.

## XXX

While XXX is a string of four lowercase letters with an X in them, there are no strings of four lowercase letters with just one other letter.

For example, you cannot have a string of four lowercase letters with just the letter I. The same goes for any other letter: there are no strings of four lowercase letters with just the letter I.

This is because the letter I is already included in the alphabet, and all the strings of four lowercase letters already have at least one instance of the letter I.

The same goes for any other letter: there are no strings of four lowercase letters with just that letter because it is already included in all strings of four lowercase letters.

There are, however, strings of five lowercase letters with just one other letter. For example, ii or ee.

## XXXX

While this is a fun fact, XXXX is not a string of letters that exists. This is because there are no strings with all four letters, X, O, X, and X.

As you can see in the image above, if you had a string with all four letters, X, O, X, and X, it would not be a string of letters. It would be an object with the letter X on it.

So while it is fun to imagine a XXXX string, you will never actually come across one. You can try looking for one as soon as you get off the plane in Australia though!

There are many things in our everyday lives that we take for granted because we are familiar with them. Things like toilets and bags become so normal that we do not think about how complicated they are.

## XXXXX

The string XXXX is incredibly rare. In fact, there is only one string of four lowercase letters that have the letter X in them.

String theory in physics is based on the idea that everything in the universe is connected through strings. These strings are said to be a fundamental unit of energy and strength. The different strands of a string can be thought of as different dimensions.

So, what if we took this theory and applied it to string theory? What if everything in the universe was connected through strings and each dimension was a different string? What kind of crazy stuff would you be able to do then? You would be able to travel between dimensions, that’s what!

This may sound crazy, but there have been studies done on interdimensional travel and some scientists believe it may be possible one day.

## XXXXXX

The string of Xs is a classic challenge. Many people have tried to find the longest string of four lowercase letters with the letter X in them, but no one has ever succeeded.

Sadly, this challenge will probably never be solved. There are just too many possible strings and far too many ways to combine the twenty-six letters of the alphabet to make even a single XXXXXX string.

Theoretically, this challenge could be solved, but it would take an unfathomable amount of time and effort. Even with the help of computers, it would take years just to sort through all the possibilities.

For your own sanity, don’t spend too much time trying to find the longest string of four lowercase letters with the letter X in them.

## XXXXXXX

The string “XXXXXX” is a very short string with only one occurrence of the letter X. This makes it a rare string, which is something to be proud of!

Interestingly, this string also has no instances of the letter X in it. That means that if you put another X in the middle of the string, it would no longer be an instance of this string. It would be a different string.

How do we know? Because we checked! We checked very carefully, too- thousands and thousands of times. We did not miss any instances of the letter X in this string. We are very careful people, even about strings that only have one instance of the letter X in them.

This is because we are professional String Checkers and we take our jobs very seriously. We want all the strings to be as good as they can be, so that when people check them they do not end up with headaches or shoulder pain from throwing them across the room in frustration.

## 9 possible strings with the letter X in them

There are nine possible strings with the letter X in them. Seven of these strings have four letters, and one has five letters. The remaining two strings have no letters!

Interestingly, all possible strings with no letters have the letter X in them. This is likely because you must have at least one letter to have the letter X in it.

There are only two possible strings with five letters that contain the letter X. One of these strings has the letter X in the middle, and one has it at the end.

The average number of possible strings with four letters and the letter X in them is 3.75. This comes from calculating the total number of possible strings with four letters (24) and dividing that by the number of possible strings with the letter X in them (9).

## Lowercase y with the letter x in it

The next string is a little tricky, but we have faith in you!

You will need to find a string that has the letter y in it, followed by the letter x. Then, you will have to find a string that has the letter y in it and ends with x.

For example, you could search for a string of four letters that have the letter y in them and end with x. You could also search for a string of four letters that have the letter y in them and then end with x twice. Both of these would count as strings xxxyyyxxy.

Surprisingly, there are no strings of four lowercase letters that have the letter y in them and end with x.