# The Simplest Math Problem No One Can Solve - Collatz Conjecture

TLDRThe Collatz Conjecture, also known as the 3x+1 problem, is a simple yet unsolved mathematical puzzle. It involves applying two rules to any chosen number: if the number is odd, multiply by three and add one; if even, divide by two. The conjecture posits that no matter which number you start with, you'll eventually enter the 4-2-1 loop and reach one. Despite its simplicity, the problem remains unproven and has perplexed mathematicians for decades. The video explores various approaches to understanding the conjecture, including randomness, Benford's law, and the idea that sequences may shrink more often than they grow. It also discusses the potential for a counterexample to exist, which would disprove the conjecture, but none has been found even after testing an immense number of sequences. The Collatz Conjecture highlights the surprising complexity and irregularity within the realm of numbers.

### Takeaways

- 🧩 The Collatz Conjecture, also known as 3N+1, is a simple yet unsolved problem in mathematics where you apply specific rules to a chosen number and observe the resulting sequence.
- 🔢 The conjecture suggests that any positive integer, when repeatedly applying the rules of multiplying by three and adding one for odd numbers or dividing by two for even numbers, will eventually reach the cycle of four, two, one, and then one.
- 🕵️♂️ Mathematicians have tested the conjecture up to very large numbers (two to the 68th power) without finding a counterexample, but a formal proof for all positive integers remains elusive.
- 📉 The sequences generated by the Collatz Conjecture exhibit a pattern similar to geometric Brownian motion, displaying a random, wiggly graph with a downward trend.
- 📊 The distribution of leading digits in the sequences follows Benford's Law, which is a logarithmic distribution where lower digits are more common, but this law does not prove the conjecture.
- 📈 The conjecture's difficulty lies in its unpredictability; even numbers close to each other can follow vastly different paths before reaching the cycle.
- ⛓ The directed graph representation of the Collatz Conjecture shows a complex network of connections that all numbers must eventually join if the conjecture is true.
- 🔍 Despite extensive computational testing, no one has been able to prove or disprove the conjecture, suggesting it may be incredibly difficult or even undecidable.
- 🤔 The conjecture raises questions about the nature of numbers and mathematics itself, highlighting the potential limits of what can be proven or disproven within the field.
- 🎨 The visual representations of the Collatz Conjecture, such as the coral-like structures formed by rotating the directed graph, demonstrate the beauty and complexity that can arise from simple mathematical operations.
- 💡 The Collatz Conjecture serves as an accessible problem that anyone can understand and engage with, illustrating the fundamental and often surprising challenges present in mathematics.

### Q & A

### What is the Collatz Conjecture?

-The Collatz Conjecture is a mathematical hypothesis that asserts every positive integer will eventually end up in the 4-2-1 loop when repeatedly applying two rules: if the number is odd, multiply by three and add one; if the number is even, divide by two.

### Who is credited with the Collatz Conjecture?

-The Collatz Conjecture is named after German mathematician Luther Collatz, who may have come up with it in the 1930s.

### What are hailstone numbers?

-Hailstone numbers are the numbers generated by applying the 3x+1 (Collatz) process. They are called hailstone numbers because they fluctuate up and down like hailstones in a thundercloud before eventually falling to one.

### Why is the Collatz Conjecture considered a difficult problem?

-The Collatz Conjecture is considered difficult because, despite its simple formulation, it has defied proof by even the world's best mathematicians. It also exhibits chaotic and unpredictable behavior, making it hard to analyze systematically.

### What did mathematician Paul Erdos say about the Collatz Conjecture?

-Paul Erdos famously said, 'Mathematics is not yet ripe enough for such questions,' highlighting the conjecture's difficulty and the current limits of mathematical understanding.

### What are the two possible ways the Collatz Conjecture could be false?

-The Collatz Conjecture could be false if either: (1) there exists a number whose sequence grows indefinitely without returning to one, or (2) there exists a sequence of numbers that forms a closed loop, unconnected to the main 4-2-1 loop.

### How have mathematicians attempted to prove the Collatz Conjecture?

-Mathematicians have attempted to prove the Collatz Conjecture by testing large numbers through brute force, analyzing the behavior of sequences, and using statistical methods to show that almost all numbers reach a point below their initial value.

### What is Benford's Law, and how does it relate to the Collatz Conjecture?

-Benford's Law describes the frequency distribution of leading digits in many real-life sets of numerical data. For the Collatz Conjecture, it shows that the leading digits of hailstone numbers follow a predictable pattern, which provides insights into the behavior of these sequences.

### What was Terry Tao's contribution to the Collatz Conjecture?

-Terry Tao showed that almost all numbers in 3x+1 sequences will end up smaller than any arbitrarily defined function f(x), as long as that function tends to infinity as x tends to infinity. This is a significant step towards proving the conjecture, but it is not a complete proof.

### Why is it difficult to prove the Collatz Conjecture using brute force?

-It is difficult to prove the Collatz Conjecture using brute force because the number space is vast, and even testing up to very large numbers like 2^68 is still relatively small on the scale of all possible numbers. This makes it impractical to search for counterexamples exhaustively.

### Outlines

### 🔢 The Enigma of the Collatz Conjecture

The Collatz Conjecture, also known as 3N+1, is a simple yet unsolved problem in mathematics that challenges even the best mathematicians. The conjecture suggests that any positive integer, when repeatedly subjected to the operations of multiplication by three and addition by one for odd numbers, or division by two for even numbers, will eventually enter the cycle of four, two, one, and then one. Despite its simplicity, the conjecture has remained unproven, with renowned mathematician Paul Erdos suggesting that mathematics is not yet ready for such questions. The process is illustrated through examples, and the video highlights the unpredictable paths, or 'hailstone numbers,' that these sequences can take, drawing parallels to geometric Brownian motion and the stock market's random fluctuations.

### 📊 Analyzing Patterns in the 3x+1 Sequence

This section delves into various analytical approaches to understanding the 3x+1 problem. It begins by examining the leading digits of hailstone numbers, revealing a pattern that aligns with Benford's law, which is observed in diverse phenomena from company values to population sizes and is even used in detecting fraud. The analysis also addresses the apparent contradiction of sequences appearing to grow on average due to the operations performed on odd and even numbers. However, it's shown that multiplying an odd number by three and adding one, followed by dividing by two, results in an average growth factor less than one, suggesting that sequences are more likely to shrink than grow. Visualizations such as directed graphs and modified coral-like structures are introduced to represent the complex paths numbers can take in the 3x+1 sequence.

### 🔍 The Search for Counterexamples and Infinite Sequences

The video discusses the ongoing efforts to prove or disprove the Collatz Conjecture by searching for counterexamples or sequences that lead to infinity. Despite extensive computational tests on numbers up to two to the 68th power, no evidence has been found to contradict the conjecture. Mathematicians have used scatterplots and various mathematical bounds to show that almost all numbers in a 3x+1 sequence will eventually become smaller than their original seed, bringing them closer to the one. Notable mathematicians like Riho Terras and Terry Tao have contributed significant findings, but a definitive proof remains elusive. The video also raises the possibility of undiscovered loops or infinite sequences that could invalidate the conjecture.

### 🤔 The Philosophical and Practical Implications of the Collatz Conjecture

This part of the video contemplates the philosophical implications of the Collatz Conjecture and its resistance to proof. It raises the question of whether the conjecture's difficulty lies in its falsity or in the limitations of current mathematical methods. The video suggests that the search for a counterexample might be as elusive as finding a needle in a haystack, given the vastness of the number space. It also touches on the Turing completeness of a generalized version of the 3x+1 problem, hinting at the possibility that the conjecture could be undecidable. The video concludes with reflections on the irregularity and peculiarity of numbers, challenging conventional perceptions of mathematical certainty.

### 🌐 The Beauty and Complexity of Mathematical Structures

The final paragraph highlights the intricate and organic beauty that emerges from simple mathematical operations, as exemplified by the coral representation of the 3x+1 problem. It invites viewers to ponder the possibility of unique, unconnected sequences that might defy the conjecture and run off to infinity. The video ends on a reflective note, with a quote from Paul Erdos suggesting that mathematics may not yet be equipped to answer such complex questions. The presenter expresses a newfound appreciation for the peculiar nature of numbers and encourages viewers to engage with mathematical problems, promoting the use of Brilliant, an interactive learning platform, to deepen their understanding of mathematical concepts.

### Mindmap

### Keywords

### 💡Collatz Conjecture

### 💡Hailstone numbers

### 💡Geometric Brownian motion

### 💡Benford's law

### 💡Terry Tao

### 💡Directed graph

### 💡Counterexamples

### 💡Turing machine

### 💡Halting problem

### 💡Polya conjecture

### 💡FRACTRAN

### Highlights

The Collatz Conjecture, also known as 3N+1, is an unsolved problem in mathematics where sequences of numbers eventually fall into a loop.

Paul Erdos suggested that mathematics may not yet be ready to solve the Collatz Conjecture.

The conjecture's rules involve multiplying an odd number by three and adding one, or dividing an even number by two.

The process generates 'hailstone numbers' that fluctuate unpredictably, similar to geometric Brownian motion.

Despite randomness, the leading digits of hailstone numbers follow Benford's Law, a common distribution pattern.

Statistical analysis shows that 3x+1 sequences tend to shrink rather than grow, due to the geometric mean of steps.

A directed graph visualization can represent the paths of numbers in the 3x+1 sequence.

If the conjecture is false, it could involve a number that starts an infinite sequence or a disconnected loop.

Mathematicians have tested every number up to 2^68 without finding a counterexample to the conjecture.

Riho Terras and others have shown that almost all Collatz sequences reach a point below their initial value.

Terry Tao demonstrated that almost all numbers in a sequence become smaller than any arbitrary function of x.

The difficulty in proving the Collatz Conjecture may suggest it's either exceptionally complex or potentially false.

The conjecture's truth could be undecidable, similar to the halting problem in computer science.

John Conway's FRACTRAN shows that mathematical machines can be Turing-complete but may never halt.

The Collatz Conjecture exemplifies the unpredictability and peculiar nature of numbers.

Brilliant.org offers interactive lessons to deepen understanding of mathematical concepts like the Pythagorean theorem.