My mind boggles

deepspacest3
Hi every one.
Im new on this forum,and my question is my reason for joining.
iv seeked this question for a long time now,and it confuses me.The answer may be very simple to a peron that already knows the answer,me on the other hand...
!!!! hasnt got a clue.

------------------------------------------

I shine a torch powerful enough to reach andromeda galaxy from earth.i understand the concept and reasoning in the distance it has to travel and the time it takes to get there.

so my question is :-

If i take that very same distance,scale it down so it fits in the palm of my hand.and on the palm of my hand is obviously a scaled down earth,with scaled down "me"then if i shine a light across my hand,from my point of view the light travels instantaneously.but the scaled down "me" will he see it at the same instant,or would it still take years to get there.??

Yours answers would be greatly appreciated,and would put an end to my mind boggling..

thanks

Last edited by a moderator:

TheTechNoir
The speed of light is unchanging in a vacuum (what I mean by that is it is slower in, say, water but that hardly factors into your question) so no matter how big or tiny you are, it will always travel at the same speed.

But my answer isn't really a good answer because it is an utterly fantasy question with nothing related to science about it at all unless I am totally missing something. But basically if there is anything scientific to get out of this it is that light will travel at the same speed regardless of your size. If light (photons) were also smaller, to scale with you and everything else then yes the light would still take the same amount of time to reach andromeda but then there is no way of saying that the light is any smaller. Being bigger or smaller than something is also relative. If every thing in our universe was 10% smaller, what does that mean? Nothing, it would have no meaning or any way to prove it. If every single thing were to stay to scale then the physics would not change.

If you don't mean to shrink the light, just the space within that specific region itself (whilst you remain the same size and everything else outside of that range also stays the same size, thus giving meaning to shrinking) and the other objects within it well then that question cannot be seriously answered, not even hypothetically as it is again pure fantasy. The amount of quantuam mechnical conflicts with that idea are staggering.

Oh and light doesn't travel across your palm instantly, if it didn't have a finite speed it would get to andromeda instantly on the real life scale as well. So in fantasy landy you can make up any answer you like, I'd go with if the light shrank as well it would not cross your palm quickly from your perspective of being bigger than the Earth, it would take the same amount of time as a normal photon (light particle/wave) to travel along the normal earth-andromeda distance. If you were small, it would again take the same amount of time except the light would seem fast to you rather than taking millions of years to cross your palm. If the light did not shrink down with you and everything behaved normally (again absurdly large issues with this outside of care bear land) it would cross your hand quickly from normal scale and from a small scale would also make the trip just as fast. But far too many issues making this impossible would cause those make-belief answers to be incorrect anways simply by virtue of not being able to happen in the first place for more reasons that can be counted.

Last edited:
deepspacest3
Thnak you very much..
it certainly answered my question and gives me satisfaction.

i know my question was fantasy.but im a physics pure noob.and space baffles me,as well as that question..thanks

Fish4Fun
deepspacest3,

Welcome to PF!

I am certain you will get a more definitive answer than mine from someone far better equipped to respond; however, here is my thought:

The premise of "scaling down" distance has two affects that create problems with your thought experiment: 1) The speed of light is a Universal Constant that involves distance, hence by "scaling down" distance you violate the validity of the speed of light. 2) Gravity is a function of mass and density. As large amounts of mass come closer and closer together the gravitational forces become so strong light cannot escape, ie a "Black Hole" forms. Because atomic distances are relatively "fixed" they are not "scalable", thus if you reduced the size of two galaxies to the palm of your hand, no light would be observable at all, and the palm of your hand would still contain the total mass.

I think your thought experiment is very interesting and quite imaginative; however, I think the closest thing to it that might be valid is to move your frame of reference to various points between the two galaxies without "scaling", but without "scaling" you would observe the light exactly as described by relativity.

As I said, I am certain others will have more eloquent thoughts on this, but that is my "off the cuff" thought.

Fish

Fish4Fun
removed double post

Rap
The physics of the universe are determined by the "dimensionless constants" of the universe, the fine structure constant, the gravitational coupling constant, etc. If they stay the same, then the physics of the universe stays the same. All lengths could change by the same amount, or all time intervals, or all masses, but if they changed in a way that kept the dimensionless constants the same, you would never know it, there would be no experiment that would detect it. You can't just change all lengths, because that would change the dimensionless constants. Other things like mass, and/or time and or electric charge etc. would have to change too. If you just changed lengths, then electrons might be more tightly bound to the nucleus of an atom, and all your chemistry would change, and you would be living in an entirely different universe. Its possible that the chemistry could change so that life was not even possible.

If you don't want to go into some wierd world, and you say that lengths will change, and other things will change so that the dimensionless constants stay the same, then you will experience nothing. The galaxies may have their distance cut in half, but so will the speed of light be cut in half. Your meter sticks will be half the size, your clocks will run twice as slow, and you will measure the speed of light to be the same number of meters per second. You will never notice any difference.

So the answer to the question is that you either live in a totally wierd universe or else it will take the same number of years (rotations of the earth around the sun) for light to travel to the other galaxy.