# Riemann's paradox: pi = infinity minus infinity | Summary and Q&A

4.8M views
β’
July 9, 2016
by
Mathologer
Riemann's paradox: pi = infinity minus infinity

## TL;DR

Mathematician demonstrates how rearranging infinite series can result in different sums, challenging conventional understanding of infinite sums.

## Key Insights

• πΉ Infinite series can be rearranged to yield different sums, challenging the conventional understanding of infinite sums.
• π» The Riemann rearrangement theorem allows for the rearrangement of convergent series to obtain any desired sum.
• π The order of terms in an infinite series matters, and rearranging the terms can create a new series with a different sum.
• π°οΈ Different types of infinite series exist, including convergent and divergent series, each with their own properties.
• πΉ Bracketing does not affect the sum of a convergent series, but it can be used creatively to obtain different sums in divergent series.
• #οΈβ£ The concept of series rearrangement applies to various mathematical areas, including complex numbers and vectors.

## Transcript

[Subtitles submitted by: ZachΓ‘ry Dorris] Today I want to let you in on a really neat trick that I learned from a very famous mathematician; how to subtract β from β to get exactly Ο. So for that I'll return to this blackboard here I found in the Simpsons, and I discussed in this video up there. And particularly that infinite series down there at th... Read More

### Q: How is it possible to subtract infinity from infinity and get a specific value like pi?

The video explains that rearranging the terms in an infinite series can result in different sums, demonstrating that the order of terms in an infinite series matters. In this case, the rearranged series yields the value of pi.

### Q: What does the Riemann rearrangement theorem state?

The Riemann rearrangement theorem states that for a convergent series whose positive terms sum to infinity and negative terms sum to negative infinity, it is possible to rearrange the series to obtain any desired sum, including pi.

### Q: Does rearranging terms in all infinite series result in different sums?

No, not all infinite series can be rearranged to yield different sums. Some series have a fixed sum no matter how the terms are rearranged, while others cannot be summed at all.

### Q: Does rearranging the terms in a convergent series affect its sum?

Yes, rearranging the terms in a convergent series can change its sum. This challenges the conventional understanding that the order of terms does not affect the sum of an infinite series.

## Summary & Key Takeaways

• The video explores a paradoxical math problem of subtracting infinity from infinity to obtain the value of pi.

• The mathematician demonstrates how rearranging the terms in an infinite series can change its sum, challenging the conventional understanding of infinite sums.

• The Riemann rearrangement theorem is introduced, which states that convergent series can be rearranged to yield any desired sum.