What is time? Is time travel possible?

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Originally posted by Tweek_1984
Thats like saying I went on a plane with a litre of water and came off with slightly less than the litre I left on the ground. Time on clocks is solid, it doesnt change if you go faster. Clocks are merely machines. How can they be altered by speed? The clocks dont know they are on planes? They should operate as normal.
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The clocks are aware they are in a moving frame of reference.

This all stems from the speed of light being the same in all inertial frames. This is obviously a problem. If you are moving faster than someone you'd see light moving at a different speed logically but this is wrong.
Becuase of this fact a whole branch of physics was created to deal with that. Its not to hard (I had a lecture proving it on Thursday) to derive a series of equations that show as your speed increases relative to an interial frame time becomes slower for you and lengths become shorter.

Its not that the clocks are dodgy in some way and when moving on the plane screw up. Since the planes are moving compared to Earth's intertial frame the very fabric of space around them alters in such a way the plane's "time dimension" slows. To people on the plane nothing happens. To a person on the ground looking at the people on the plane the people on the plane would be moving slower than normal (obviously for a plane there isn't a noticable difference but if the plane moved at half the speed of light it'd be very obvious).

I think of it as, we are living in a 4 dimensional universe. 3 spacial and 1 temporal. If you move faster in the spacial dimensions you slow in the temporal dimension. Its like we have a "total" speed over the 4 dimensions. We are unaware of the time one really, but we can notice when he are moving in the spacial. Moving quickly in the spacial reduces our speed in time so we slow down.

I've a book on time travel and about things like logical paradoxes. Some things can#t be allowed, while others are possible.

There are methods of time travel that allow travel to the past but they all involve things like "an infinite length rotating cylinder" or for the universe to have a certain curvature which doesn't appear to be the same as our universes.

Other problems arrive when talking about travelling into the past, not just the "kill yourself" one. Look at Terminator. The machines send back The Terminator to kill Sarah. He fails but leaves behind his brain chip and an arm. From these remains the company creates the new computer chips, Skylab is built from that and the Machines are born. But who invented the CPU technology? The machines are based on it, but it was manufactured by the company who got the design from the machines, hence an infinite loop. This technology appears to have just created itself in the universe. Hmmm.......

I've got my 4th Special Relativity lecture tomorrow. Even though its Bank Holiday Monday I've got 2 hours of lectures at 10am......:rolleyes:
 
I thought up a theoretical device that shifts your current brain pattern into a previous or alternate state.

Then i realised perhaps we do it often,perhaps on a quantum scale our memory is not memory at all but time travel,hence the reason you cannot remember anything to full extent,you actually mentally travel backwards,not physically but you cant hold that thought for long,memory is not that effective.

Also:dreams,perhaps some(not all) dreams are images of what an alternate you is seeing in alternate timelines/universes.

Your not gonna remember much when waking up cos memory is like that as i stated already.

Our memory is not memory,its not coherent,i can think back willingly but its hard to see everything in any detail,your senses dont quiet shift but at the same time they do,memory is vague,it supposedly all seems to be there but is not if you get what i mean.

By rights if memory is only memory,you should not be able to remember what something tastes like without actually tasting it,but you can almost if you physically decide "hmmn let me think what that pizza tasted like" and you can almost taste it.

Truth is our memory is selectable,i can remember a few minutes ago in vague detail,and distant past in vague detail.

All this BS about long term,medium term memory is rubbish,its all the same,memory is memory unless you get brain damaged,and thats still to do with brain neurons.

You are technically both brain damaged and paralised when you are asleep,then you wake up and memory of the dreams is the same as in waking life memory:vague and selective.

Them two words are important:vague and selective

Memory,true memory might not work the way we think,it certainly dont seem to be a storehouse cos why cant i remember anything except what i might choose to remember,yet it all seems to be there.
 
go to bookshop, buy "a brief history of time" by stephen hawking, get confused but have a slightly better idea of whats going on...

time traveling though, if time stops when when traveling at the speed of light, then if you go faster than the speed of light then it would go backwards? (though aparently nothing can go faster than the speed of light)
afik time is not linear, were set on the idea that 10minutes here means ten minutes somewhere else.
ok 2 identical twins
twin a stays on earth
twin b is fired into space at the speed of light and returns in 40years time
twin a has aged 40 years, twin b has not aged (at least not as much)
so time for twin a is not the the same as twin b, therefore time is not the same everywhere...
*may not make any sense at all, believe what i say at your peril
 
Yes energy could be accelerated at more than the speed of light,its just mass you cant get to that speed as it needs infinite energy.

If something is not made of mass it could be made to go faster than light,in which case it goes backwards in time.

Tachyons are theoretical,some have argued there proof,but if they exist they go faster than light.

You could use them to go back in time,or maybe send messages back in time.
 
Time dilation (shortning of time) has been proved in the lab using atomic clocks. Currently there are at least 10 well known experiments proving general & special relativity alike (i.e. the precesion of Mecury around the sun - the perhilion effect)

Before saying "time slowing down = impossible/i think it's stupid etc..." have a read of some popular science books/websites and read the evidence that proves the theory!

Pj

PS

Here's one to get your heads around:

Imagine a pair of scissors, not your ordinary house hold variety - a galactic pair - with blades 3-4 light years long.

When the scissors are open, the blades at the very end are about 1 light year apart.

Now you close the scissors which takes about 1 second.

If the blades close together over a period of 1 second, this means that the ends of the scissors have travelled half a light year (remember both blades are about 1 light year apart) in a matter of seconds. But things can't travel faster than the speed of light can they?! :confused: :D
 
Originally posted by Pj·uK
Here's one to get your heads around:

Imagine a pair of scissors, not your ordinary house hold variety - a galactic pair - with blades 3-4 light years long.

When the scissors are open, the blades at the very end are about 1 light year apart.

Now you close the scissors which takes about 1 second.

If the blades close together over a period of 1 second, this means that the ends of the scissors have travelled half a light year (remember both blades are about 1 light year apart) in a matter of seconds. But things can't travel faster than the speed of light can they?! :confused: :D
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Oh oh, I know, I know but I'll wait to see what other people say :p
 
Yip time travel is possible, when I go to sleep at night the last thing I can remember is beginning to fall asleep. Then suddenly it's morning and time to get up, to me it happens almost in no time but in fact it's around 8hrs later :p
 
The only known constant in our universe is the speed of light, as somebody said, time is relative to your speed.

Using this - isn't it true that time travel is possible, you just need enough speed?

i.e. We travel at the speed of light for two minutes, by the time we come out, we're 20 years in the future. Hence we have travelled forward in time?
 
Originally posted by iam
We travel at the speed of light for two minutes, by the time we come out, we're 20 years in the future. Hence we have travelled forward in time?
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That's possible iff you could reach the speed of light or at least a fraction of the speed.

I think what's being discussed is actually travelling back in time!

Pj
 
I reamember at school my science teacher was talking about this kind of thing and said that if you had a very powerful telescope ( bigger than hubble of course) and was on pluto and pointed it to the Earth, for instence, you would see back in time becuase of how long time takes to travel that kind of distance.


Kinda interesting, if you coulds go faster thant time to get there then you could "see" the past...............
 
well yes that obvious, i mean it takes 8 minutes for the light from the sun to reach us so we are looking at the sun as it was 8 minutes ago. its not possible to travel back in time int he back to the future type of way, as alpahnumeric said (if i've understood it) is that if the universe (i.e spacetime) is cylcindrical then it will eventually all startr over again or summit.

the problem about going the speed of light is that the closer you get to it the more mass you have, and obviously for more mass then you need more energy, hence that it not possible to get to the speed of light as it would take infintie engergy.
 
People have hypothesised about paradoxes,parallel worlds and so on,but the truth is we dont actually know what will happen if a time machine/device was made that supposedly can transport people through time.

We think about it in human/memory and common sense terms,but very often common sense can be wrong.

I mean if i took a laptop computer back in time to 200 years ago,the laptop would defy common sense of the time,there is NO possible way the people of the time could understand how it works without complete explanation,it would seem like a gift of the gods or a satanic/magic trick,even back then.

Classical physics did not allow for a computer,only quantum physics made what your sitting at possible.

A unification and quantum theory of gravity would give us more info on if time travel is possible,as of yet we really dont understand gravity in any more than classical terms.
 
Originally posted by AlphaNumeric
I think of it as, we are living in a 4 dimensional universe. 3 spacial and 1 temporal. If you move faster in the spacial dimensions you slow in the temporal dimension. Its like we have a "total" speed over the 4 dimensions. We are unaware of the time one really, but we can notice when he are moving in the spacial. Moving quickly in the spacial reduces our speed in time so we slow down.
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Hmm supposedly 11 dimensions, although some may have collapsed according to M thoerists.

We are talking about physics on the scale of Planks length.
 
Originally posted by mctiny
I reamember at school my science teacher was talking about this kind of thing and said that if you had a very powerful telescope ( bigger than hubble of course) and was on pluto and pointed it to the Earth, for instence, you would see back in time becuase of how long time takes to travel that kind of distance.


Kinda interesting, if you coulds go faster thant time to get there then you could "see" the past...............
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If you could get infront of the light for the period then yes you could measure and record the light however it would prove difficult mainly because of the gravitation lens effects of objects in space.
 
Hmmm well, here goes.......

Re: the scissor thing:

You won't be able to close them. As the ends start moving they will get heavier and heavier and reach infinite mass as they hit the speed of light. the material will then bend and nothing will travel faster than light. THat's if you have enough energy to close them at all.

Time is a dimension. Here is an analogy:

You are in a room, a very long room and you are walking backwards at a set rate. This is similar to how we progress through time. We can see what has just happened (what we have walked past) but we cannot see what lies ahead (because we are walking backwards. Now imagine an event that is going to occur in the future. We havn't got to it yet, so cannot see it because it's in the future. However that does not mean that that event will not happen. I'm not a great believer in fate or destiny and that is why. All events in time have already happened - we just havn't got there yet.

If you could travel at the speed of light, time would stop and you would be infinitely heavy. Therefore from your point of view, it would take no time at all to travel 3 million light years because time has stopped. However, to the stationary observer, it would take you 3 million years. Time is relative like that. If you could go faster than light, you would get to the end point before you left, but only from your point of view. Paradox. (usually equals somethings gone wrong).

It's possible to create all sorts of paradoxes in time travel. eg.

You have a rocket missile pointed at a transmitting station. The transmitting station is the only thing that can tell the missile to fire. Also, the transmitter has the ability to send messages through time. When the missile is fired, it will hit the transmitter and destroy it. Someone decides to tell the transmitter to send the fire command back 1 hour in time. 1 hour before that fire command is sent, the missile destroys the transmitter, so there is no transmitter to be destroyed. Now, going back to my original concept that all events are fixed in time - in other words there always was a transmitter there to send that signal and you cannot change that, you have a paradox. If it is possible to send messages back in time, then in that situation the missile cannot have been launched and the transmitter cannot have been destroyed because they are still there an hour after the command was sent.

I think.
 
Originally posted by growse
You won't be able to close them. As the ends start moving they will get heavier and heavier and reach infinite mass as they hit the speed of light. the material will then bend and nothing will travel faster than light. THat's if you have enough energy to close them at all.
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Not quite...you're correct about the scissors flexing - but the wrong reason for them flexing!
 
If you think about object and events as having a "light cone", then it's easier to think about time... Anything outside of the light cone of an event cannot know that it has happened. Only once the light cone encompasses 'you' can you know that it has happened. For instance, the earth enter the sun's light cone after 8 minutes. If the sun blew up, we would have no idea that anything happened until 8 minutes after the actual event. If you could travel faster than the speed of light, you could be at the sun, and watch it explode. You could then travel to the earth faster than the light (and all EM frequencies) and thus warn the people that it is going to happen. Of course, they would still only be able to find out a maximum of 8 minutes before the event, but it is time travel in a way. You couldn't change the event, but you could alter it's effects.
 
Originally posted by Pj·uK
Time dilation (shortning of time) has been proved in the lab using atomic clocks. Currently there are at least 10 well known experiments proving general & special relativity alike (i.e. the precesion of Mecury around the sun - the perhilion effect)

Before saying "time slowing down = impossible/i think it's stupid etc..." have a read of some popular science books/websites and read the evidence that proves the theory!

Pj

PS

Here's one to get your heads around:

Imagine a pair of scissors, not your ordinary house hold variety - a galactic pair - with blades 3-4 light years long.

When the scissors are open, the blades at the very end are about 1 light year apart.

Now you close the scissors which takes about 1 second.

If the blades close together over a period of 1 second, this means that the ends of the scissors have travelled half a light year (remember both blades are about 1 light year apart) in a matter of seconds. But things can't travel faster than the speed of light can they?! :confused: :D
Click to expand...

It means they have travelled half a light year in half a second each,
186,000 miles per second is light speed,if youve only moved half a second then you have only moved half that distance,but both blades are doing both distances so they will touch at half the speed of light.
 
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