Final answer:
The interval notation for all real numbers is (-∞, ∞), which includes every number from negative to positive infinity, using parentheses to indicate that infinity itself is not included.
Step-by-step explanation:
The interval notation for all real numbers is (-∞, ∞). This notation means that the interval includes all numbers from negative infinity to positive infinity. It's important to understand that the use of parentheses in this context signifies that infinity is not a real number that can be reached or included, hence open intervals are used. Real numbers include both rational and irrational numbers, extending indefinitely in both the positive and negative directions on the number line.