Andy G asked in Science & MathematicsMathematics · 1 decade ago

# STRAIGHT LINES:Is there really such a thing as a straight line?

Crude example: if you was to build a wall the top must be straight (you use a spirit level to make sure the top is straight and level) if you kept on building the wall would it go around the world (the world is round but the wall is straight)

Update:

Added: if space and the universe is curved surely all straight lines are an illusion

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• Anonymous

A good question as it raises the point, what is a straight line? There is a fair amount of discussion about this in Heath's translation of Euclid's elements (Book 1) and this amount to what we were told at school that it is 'the shortest distance between two points.' That is in the flat plane of course. The shortest distance between two points in a curved plane (staying in the plane) is a curved line but does anyone know if that amounts to a straight line when dealing with non-Euclidean geometry?

• 1 decade ago

There is; using your example, to build a wall, you'd use a plumb line. That hangs vertically in a straight line. If you hung one 30ft away, due to the curvature of the earth they wouldn't be completely paralell, but both would be straight (even taking into account the fact that the earth is spinning, moving round the sun, the sun is moving in the galaxy and the galaxy is moving in all sorts of strange directions).

If you used a laser line to build the wall, that would be straight but your wall would get higher as the earth curved away.

• 1 decade ago

yes, there is such a thing as a straight line.

However, In your example, it depends on the type of spirit level that you used. if it is a liquid bubble type, the spirit level is reacting to gravity, so the wall would (over the course of many metres) actually be curved

if you used a laser beam spirit level, you could achieve a wall, which would be straight, and would get bigger as the curvature of the earth started to disappear beneath it

• Anonymous

Yes.

The world is VERY big so it would be straight but it would bend eventually around the world.

But that is a bad example because even though it is supposed to be straight it is tricking the mind.

There is such thing as a straight line, drawn or not for example: ______ , < that is a straight line...

(:

• 1 decade ago

your example has a false assumption: that gravity is perpendicular to the line and gravity always points the same direction (at any place the direction of gravity is parallel to the other places, which is false).

I do agree that it is possible, given your assumption of curved space and universe, that what we perceive as straight lines may not in fact be "straight". However, there still must be some real straight lines, even if we may perceive them as not straight.

• Anonymous

Yes, there is really such thing as a straight line.

• 1 decade ago

Of course there is. Proof? The whole Algebra 1 is all about it

.

• 1 decade ago

if you believe in infinity,u must believe on straight lines >>>