# Past brilliant physics problem about Euler's Characteristic?

Someone please help me understand this problem. I thought there are no well-explained answers from the user and also brilliant staff did not give any single comment on that problem. Thanks for your help :)

Note by Nabila Nida Rafida
5 years ago

MarkdownAppears as
*italics* or _italics_ italics
**bold** or __bold__ bold
- bulleted- list
• bulleted
• list
1. numbered2. list
1. numbered
2. list
Note: you must add a full line of space before and after lists for them to show up correctly
paragraph 1paragraph 2

paragraph 1

paragraph 2

[example link](https://brilliant.org)example link
> This is a quote
This is a quote
    # I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
# I indented these lines
# 4 spaces, and now they show
# up as a code block.

print "hello world"
MathAppears as
Remember to wrap math in $$...$$ or $...$ to ensure proper formatting.
2 \times 3 $$2 \times 3$$
2^{34} $$2^{34}$$
a_{i-1} $$a_{i-1}$$
\frac{2}{3} $$\frac{2}{3}$$
\sqrt{2} $$\sqrt{2}$$
\sum_{i=1}^3 $$\sum_{i=1}^3$$
\sin \theta $$\sin \theta$$
\boxed{123} $$\boxed{123}$$

Sort by:

While discussions about specific problems should go in solution discussions, Nabila is correct that the solutions given in the discussions may not be very enlightening to the layperson. Hence feel free to discuss it here. If no answer is forthcoming I will answer in a day or so.

Staff - 5 years ago

- 5 years ago

Thanks, I have read some references but unfortunately did not come up with $$?$$ as the answer.

- 5 years ago

If I'm not mistaken, this seems to be an application of the Gauss-Bonnet theorem - the fact that the test charge accelerates away at a point tells us something about the curvature there.

It feels a little strange to include this problem for Brilliant.

- 5 years ago

- 5 years ago

same here

- 5 years ago

Sorry, I think I gave the wrong one. But the staff has fixed it :)

- 5 years ago

My intuition on that problem is as follows: We know that charges accelerate when subjected to an electric field, but the only field source in this universe is your charge dq. Therefore, it must somehow be subject to its own field in a non-symmetrical way. The only way this could be is if the electric field came back upon dq as it went to infinity, implying that we have to be dealing with a shape with 1 face (if it has two faces, a similar self-mapping occurs, but it will always have a zero point, see the Hairy Ball Theorem). Since all topological spaces with 1 face (mobius strip, klein bottle, etc) have characteristic 0, we have our solution.

- 5 years ago

Hi Nabila,

Staff - 5 years ago

Thanks Peter, for your help :)

- 5 years ago

Yes, Nabila is talking about that problem. The link Nabila posted works for me.

- 5 years ago

You must share the problem and then post the link of the problem to let us see the problem.

- 5 years ago

The link has been edited though, go check it :)

- 5 years ago