# Guessing is a four-letter word

This is my first riddle here — I hope it's not too easy.

I killed my brother a long time ago,

My relatives are weaker, shorter;

But I may be wrong alone.

Hint:

All I'm saying is, it's hard to decide.

Edit: a hint/spoiler.

The first line is to be taken literally (i.e., actual murder, although pertaining to mythological or legendary characters).

• And if I'm right, running fast won't help you. What's this line justify? – Numberknot Aug 21 '16 at 3:51
• @numberknot What do you mean? It's part of the puzzle. (What specifically would you like to know?) – Clement C. Aug 21 '16 at 4:05
• Got it......... – Numberknot Aug 21 '16 at 4:10
• With regard to the votes to close: I added a hint (and a tag). Does it look better now? – Clement C. Aug 21 '16 at 12:34
• People sometimes give more hints over time - ideally the whole thing should be unambiguously solvable without recourse to the hints though. – A E Aug 21 '16 at 20:47

Maybe it is

Seth

I killed my brother a long time ago

Seth killed Osiris, his brother, in Egyptian Mythology.

Strong exponential time hypothesis (SETH). If this hypothesis is right, there cannot be algorithms such that k-SAT problems in Computer Science can be solved in subexponential time. So a computer running fast would not make much difference.

My relatives are weaker, shorter

SETH is a stronger form of Exponential Time Hypothesis. This could be related to Seth, the deity too, I guess.

But I may be wrong alone

SETH implies ETH. So if ETH is false so is SETH.

Note:

I did not know of SETH before this riddle so I might have made mistakes or missed stuff on the computer science part.

• This is it! The last two clues are (very slightly) off, but that's the gist. – Clement C. Aug 22 '16 at 11:03
• In particular: the two relatives are ETH (Exponential-Time Hypothesis) and SH (Satisfiability Hypothesis), both weaker conjectures than SETH (and shorter: 3 and 2 letters only). In particular, they might both hold, while SETH is proven false. As for the hint... it's all about the hardness of deciding satisfiability of a formula. – Clement C. Aug 22 '16 at 12:39

Are you planet

MARS

I killed my brother a long time ago,

Phaeton is the hypothetical planet to have existed between the orbits of Mars and Jupiter whose destruction supposedly led to the formation of the asteroid belt

you would not escape from mars gravity by running fast on earth.

My relatives are weaker, shorter

Mars has two moons, Phobos and Deimos which are relatively shorter and weak compared to mars.

But I may be wrong alone.

Mars doen't stays in its orbit if it were alone in the solar system.

And

all of these facts are hard to decide

• Good thinking, but not the answer I have in mind. – Clement C. Aug 21 '16 at 10:49

I think the solution might be

fact.

Explanation:

I killed my brother a long time ago:

The brother that was killed would be believe, as facts kill believes, either by turning them into knowledge, or by disproving them. Starting to disprove believes by facts indeed started a long time ago, in Greek philosophy.

You cannot escape the hard facts (I take "running fast" as metaphorical here, like running from the truth).

My relatives are weaker, shorter:

Relatives might be believe, hypothesis, assumption, possibility — all are weaker than a fact, as they are less certain. I have no idea how "shorter" fits in, though.

But I may be wrong alone:

A fact can in general only be decided in a context. For example "it is raining" may be true or false, depending on whether you are saying it on a rainy day or on a sunny day.

Hint:

Many facts are hard to decide.

Edit:

The riddle has the science tag. Science is all about facts.

• There are good points, but this is not the answer. I added a tag (found out about it), this may help. – Clement C. Aug 21 '16 at 12:30

It could be

Cain

I killed my brother a long time ago,

Cain killed Abel in the bible story.

The other lines I'm not 100% sure about, but the title and tags suggest

guessing a password, which is what the Cain software by Microsoft does.

• That an interesting connection (I didn't know about that software), but not what I am looking for. – Clement C. Aug 21 '16 at 19:26