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I wonder if ?

Seafury

By Seafury
in The Astro Lounge

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Seafury

Seafury

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Hi guys just thinking daft thoughts, but, if there was a star 2000 light years away we are seeing that star tonight as it was 2000 years ago, now if there was a planet going round that star and tonight in real time there was a bloke on it looking at us with a telescope or whatever powerful enough to see someone standing on earth( pure fiction I know) would he be looking at a Roman invading Britain ? and in another 2000 years he would seeus taking to the skies?

Gordon

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sologuitarist61

sologuitarist61

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Hi Gordon - yes absolutely, he would be seeing the Earth as it was 2000 years ago.

It is a strange thought though isn't it? We are used to thinking that what we are looking at happened some time previously, depending on the distance, but we often don't think of it the other way around do we? Interesting question. Hope you are well. :smiley:

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Seafury

Seafury

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Hi Richard I'm fine and you, so to take that thought further assuming during that 2000 years we had discovered a way of travelling to stars very quickly we could go to that star tonight in real time and also look through his telescope and see our ancestors, have I just invented time travel lol

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sologuitarist61

sologuitarist61

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Hi Richard I'm fine and you, so to take that thought further assuming during that 2000 years we had discovered a way of travelling to stars very quickly we could go to that star tonight in real time and also look through his telescope and see our ancestors, have I just invented time travel lol

Not sure it would work like that Gordon and the reasons I say that are summed up in your last two words - time travel. We seems to be up against two impossible things here, which are (or seem to be) impossible. 1) you can't go faster than light and 2) you can't travel back in time.

It does seem strange because in your example, the same underlying principle applies and travelling that fast is the same as time travel - perhaps that is the reason why the speed of light cannot be exceeded - it stops us being in two places at the same time.

That's my musings on the subject anyway - always happy to be proved wrong though.

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Keiran

Keiran

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Hi Gordon,

How about this thought then, If you left earth at the speed of light and continued to look back at earth, you would see it the same as when you left it. it would look like somebody had paused time....

Your first thought is correct, but the second would be correct if you could travel faster than the speed of light, but as far as we know, we cant travel faster than 670616629 miles per hour

Keiran.

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Welrod50

Welrod50

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What a great post! ;)

I think that we could go faster than the speed of light as it has a definable top speed. If we made a spaceship which could go at light speed +1 mph then we would overtake light and get there before we left.

What if there were a galaxy out there which was expanding at the same speed. The light given off by it's own stars is given off at light speed, but the galaxy is careering towards us faster than the light it gives off (?) It would collide with the Miljy Way (and us) before we ever saw it coming.

It would work like firing a bullet in a gun at say, 500 ft/sec and you do this whilst hanging out the window of an aeroplane travelling at 501 ft/sec - the bullet would never leave the gun.

As for time travel, time is relative. Make a wristwatch with undersized cogs and after one day it shows a time several hours ago, when every other wristwatch in the world is correct. Have you travelled back in time??

I'm stopping now. My brain is hurting.

The wife, power up the DeLorean.......................

Scott :Envy:

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Emperor315

Emperor315

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I love thinking about these sorts of things. I was looking at M31 - Andromeda - just an hour or so ago and thinking about how Homo habilis were walking the Earth when the light hitting my eye, left Andromeda.

"All we ever see of stars are their old photographs" - Dr. Manhattan/Alan Moore

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ollypenrice

ollypenrice

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It would work like firing a bullet in a gun at say, 500 ft/sec and you do this whilst hanging out the window of an aeroplane travelling at 501 ft/sec - the bullet would never leave the gun.

Sure, the bullet will leave the gun! The explosive charge kicks back against the back of the gun and powers the bullet relative to the gun at its usual speed. Now if you were trying to shoot someone on the ground, positioned behind the aeroplane, then you mmight be disappointed because you have to subtract the plane's speed from the bullet's speed. But if you shot at someone in front of the plane you add the plane's speed to the bullet's speed and get a superfast bullet.

This was all thought through by Gallileo in the early 1600s. We now call it Gallilean Relativity.

Olly

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jimmyjamjoejoe

jimmyjamjoejoe

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I'd recommend a book called "why does e=mc2 (and why should we care?)". It'd answer most of the questions in this thread. It deals with relativity, the speed of light, and actually does a really good job of explaining spacetime, which is something most of us struggle to grasp as a concept.

It can be a bit of a tough read in places, but it's worth reading a few of the sentences 2-3 times, because when you finally grasp some of these things, it leads to some fulfilling "eureka!" moments.

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melsky

melsky

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Hi Richard I'm fine and you, so to take that thought further assuming during that 2000 years we had discovered a way of travelling to stars very quickly we could go to that star tonight in real time and also look through his telescope and see our ancestors, have I just invented time travel lol

Surely all we need to do is discover a really big mirror 1000 light years away then we don't have to go anywhere or break any laws of physics :grin:

Mel

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Welrod50

Welrod50

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if you are in an airliner travelling at 500 mph and you ran up the aisle at 10 mph how fast are you going relative to the ground 510 mph makes Usane Bolt look a bit sick

:D If Usane Bolt was on the airliner and he flicked a coin in the air, then surely the coin would rapidly vanish towards the back of the plane and hit the back, as it is now supported only by fresh air which the plane is travelling through !? :huh:

Sure, the bullet will leave the gun! The explosive charge kicks back against the back of the gun and powers the bullet relative to the gun at its usual speed. Now if you were trying to shoot someone on the ground, positioned behind the aeroplane, then you mmight be disappointed because you have to subtract the plane's speed from the bullet's speed. But if you shot at someone in front of the plane you add the plane's speed to the bullet's speed and get a superfast bullet.

This was all thought through by Gallileo in the early 1600s. We now call it Gallilean Relativity.

Olly

I'm not so sure the bullet would leave the gun?! The bullet never makes it beyond 500 ft/sec and the gun and gun barrel is moving more quickly so surely the laws of physics dictate this?? Anyway, it is all just a bit of fun :) Until I try it next time I'm on a plane going on my hols. I will report back when I've tried it ;)

Clear skies

Scott.

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Cath

Cath

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If you could travel at the speed of light, your journey from one side of the observable universe to the other side would be over instantly (from your point of view). From an observers point of view (ie, someone on Earth), it would appear to take you over 27 billion years.

The universe is a strange place indeed!

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Keiran

Keiran

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I promise Scott im not picking on you but...

I think that we could go faster than the speed of light as it has a definable top speed. If we made a spaceship which could go at light speed +1 mph then we would overtake light and get there before we left.

Unforturnatly its not as easy as saying if we travel +1 mph faster than the speed of light we are going faster than it. It is very complicated, but you need infinate energy to accelerate a particle to the speed of light. My brain is too small to fully understad it, but have a read of http://en.wikipedia.org/wiki/Special_relativity Special relativity....

It would work like firing a bullet in a gun at say, 500 ft/sec and you do this whilst hanging out the window of an aeroplane travelling at 501 ft/sec - the bullet would never leave the gun.

The bullet will travel faster than the plane, it will be accelerating at 500ft/s away from the plane, so will look like 1001ft/s from someone standing stationary on the ground.

Have a watch of...

his lecture and way of thinking are great.

Keiran

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Welrod50

Welrod50

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Keiran, it most certainly gets the old grey matter ticking!

There are all sorts of things we can ponder over, but when it all boils down to it, the Universe is indeed, a strange place and the laws of physics both fascinating and bizarre at the same time. Makes me wonder if there may be another world out there somewhere with different laws of physics?

Scott :)

ps I know you're not picking on me :D And the train vid is very good......

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skywatcher250

skywatcher250

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what a fantastic thread... ok so welrod makes a great point (one which i have never thought of before) - if somehow the Speed Of Light CAN be exceeded, you can get anywhere without being seen as your light wouldnt have got there yet... come to think of it - if your light hasnt got there yet then maybe you havent got there yet even though you are already there.... ok maybe that explains why the S.O.L. apparantly cant be broken.... this comes back to that fantastic Brian Cox train episode - (think thats the video above but i cant play it at the min ? ) where if the train was almost at the speed of light and you ran along it you would run in slow motion

i LOVE space !!!

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Keiran

Keiran

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Makes me wonder if there may be another world out there somewhere with different laws of physics?

Scott :)

ps I know you're not picking on me :D And the train vid is very good......

Thats actually a good point you make there, I cant remember what book i read it in, i think it was stephen hawking, he said, our universe may be one of many universes out side of our own, and these universes may have different laws of physics. we will never know though, because we can not see past our observable universe.... Damn the speed of light :)

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