Time travel possible?

veXual

Hellrazer wrote: »

If you were to travel at the speed of light for exactly one year then surely you`d end up "one light year" away from where you started--no??

Now for the confusing bit-assuming the above is true---would you age by 1 year and would you notice that year passing?

I remember reading something that taking the above as an example ie you travelled 1 year at the speed of light (one light year) then a year would pass normally for you (the traveller) but on your return in 2 years of your time(ie travelling 2 light years) you would find that the earth had aged by a few hundred or few thousand years??

Very confusing!!!

If you spend a year travelling at the speed of light you would surely notice that time pass i.e. you would age by a year and notice the passage of a year.

Why would the earth have aged by a few thousand years upon your return? If you spend a year traveling at the speed of light are you not just covering a large distance?

Im not arguing with you because your point is completely valid merely presenting mine.

And yes it's hella confusing!

Hellrazer

veXual wrote: »

Why would the earth have aged by a few thousand years upon your return? If you spend a year traveling at the speed of light are you not just covering a large distance?

I think its something to do with the fact that youre travelling so fast in relative to earth so that even though only 2 years have passed for you then earth has aged more--I hope someone corrects me on this because Ive been trying to remember where I read it or even if what I read is correct.

AlmightyCushion

Hellrazer wrote: »

I think its something to do with the fact that youre travelling so fast in relative to earth so that even though only 2 years have passed for you then earth has aged more--I hope someone corrects me on this because Ive been trying to remember where I read it or even if what I read is correct.

So basically, the closer you get to the speed of light, the more time slows down.

narac

veXual wrote: »

If you spend a year travelling at the speed of light you would surely notice that time pass i.e. you would age by a year and notice the passage of a year.

Why would the earth have aged by a few thousand years upon your return? If you spend a year traveling at the speed of light are you not just covering a large distance?

Im not arguing with you because your point is completely valid merely presenting mine.

And yes it's hella confusing!

Ok. Remember that time is experienced differently for the person travelling at the speed of light, and for those that are not.

If a traveller travels at the speed of light, no time passes for them, and they can reach any point in the universe without any time passing. So, from the travellers point of view, they can't travel at the speed of light for a year, because wherever they wanted to go, they would be there instantly!

To the casual observer, though, if they observe the traveller travelling at the speed of light for one year, the traveller would end up one lightyear away from them.

This whole thing leads to some other mind boggling conclusions as well. Since it takes a photon zero time to reach any point in the universe, there is zero distance between a photon and any other point in the universe. Thus, every photon "touches" everything else in the universe, at the same time. Screwed up, I know.

Hellrazer wrote: »

I think its something to do with the fact that youre travelling so fast in relative to earth so that even though only 2 years have passed for you then earth has aged more--I hope someone corrects me on this because Ive been trying to remember where I read it or even if what I read is correct.

Again, this is true if you travel for a year at close to the speed of light. You cannot travel at the speed of light for a year (from your observation point).

AlmightyCushion wrote: »

If you travel at the exactly the speed of light then I imagine if you were to look out your windows that for the duration of your trip you would see exactly what you seen when you started your trip. Because the light that was around you when you started the trip is travelling at the same speed as you. Although that doesn't sound correct to me. As for travelling faster than light, that's quite hard to imagine. Maybe you see everything like it's in fast forward.

No. Relativity tells us that no matter how fast we travel, light always travels at the same speed relative to us. So if we are travelling at 99% of the speed of light, and measure the speed of a passing photon, that photon would appear to us to be travelling at the full speed of light and not the 1% of the speed of light we would expect. This is related to the time dilation we would experience travelling at this speed - because time has slowed for us, everything else in the universe (from our point of view) has "sped up". Thus the 1% velocity difference has "sped up" to the full speed of light.

Hellrazer

narac wrote: »

If a traveller travels at the speed of light, no time passes for them, and they can reach any point in the universe without any time passing. So, from the travellers point of view, they can't travel at the speed of light for a year, because wherever they wanted to go, they would be there instantly!

This is the bit that has me confused.You say that if I travel at the speed of light then no time passes at all and I arrive at my destination instantly no matter what the distance??
Thats even more confusing than I first thought.I always assumed that you noticed the time passing just as someone not travelling at the speed of light did.

To the casual observer, though, if they observe the traveller travelling at the speed of light for one year, the traveller would end up one lightyear away from them.

So even though no time passes for me (the traveller), for the outside observer they see time passing at their own rate relative to me??

Again, this is true if you travel for a year at close to the speed of light. You cannot travel at the speed of light for a year (from your observation point).

See now its making sense.If you get there instantly you cannot travel for longer than an "instant"


So now for the next question--If I somehow manage to travel at the speed of light and can get to any destination in the universe instantly does that mean that no time will pass for the "observer" on earth?


So I make a trip of 1000 light years"in an instant" and spend a year at my destination exploring or whatever and journey back to earth "in an instant" then only 1 year will pass for the earth aswell--assuming Im using "earth time" as my time keeping method??

You also mentioned that photons exist everywhere at the same time--then how is it that scientists are always telling us that light ie photons from a distant star took millions or billions of years to reach us and we are looking backwards in time??
Surely if they exist at every location at the same time then what we are seeing is happening "now"??

My head hurts!!!!

Gurgle

Hellrazer wrote: »

So now for the next question--If I somehow manage to travel at the speed of light and can get to any destination in the universe instantly does that mean that no time will pass for the "observer" on earth?

No, time passes as normal for the observer on earth. Its only from the relative perspective of the person travelling at the speed of light that no time passes.

So I make a trip of 1000 light years"in an instant" and spend a year at my destination exploring or whatever and journey back to earth "in an instant" then only 1 year will pass for the earth aswell--assuming Im using "earth time" as my time keeping method??

You can't use earth time as a keeping method, because you travelled from the earth at the speed of light. A year passes for you while you're there, 2,001 years pass on earth while you're gone.

Hellrazer

Gurgle wrote: »

You can't use earth time as a keeping method, because you travelled from the earth at the speed of light. A year passes for you while you're there, 2,001 years pass on earth while you're gone.

Can you explain how the 2001 years pass for earth when Im travelling instantly to my destination?
I leave Earth today 25/8/2009 and travel 1000 Light years "in an instant" according to narac`s earlier post.

I keep my own clock with me--so Im only using earth time because thats what my body is used to ie 365 days on a day/night cycle--Stick with me here.

So I arrive at my destination instantly on the 25/8/2009--I spend 1 earth year (only according to my clock) on the planet and return on 25/8/2010 again according to my clock.

So does a year pass for earth or is it the 2001 years like you say.Assuming Im travelling in an instant and spend 365 days there according to my clock which is keeping earth time for reference only?

My assumption is that only 1 year passes for earth aswell as myself.

Brouhaha

Time as experienced by an individual is affected by gravity so time on the top floor of a building will be slightly "faster" than on the bottom floor. If you want to time-travel go up-stairs for a while.

Documentary

By the way the effects of speed on time are adjusted for in GPS satellites as their very accurate time signals would appear distorted otherwise.

Gurgle

Its worth pointing out that the whole sci-fi notion of travelling backwards in time is pure makey-uppey stuff.

It only works if you make two contradictary assumptions:

1) Relativity is correct, at the speed of light you need infinite energy to accelerate any further.

2) Its possible to accelerate beyond the speed of light

So why are these assumptions contradictory:
To accelerate is to increase your velocity. If you have mass, this means increasing your momentum.

This means adding energy. Generally, you can increase your momentum by adding a finite amount of energy, but at the speed of light you have to add that energy in zero time(because time has stopped).

Your power (energy per unit time) is x / 0 = infinity.

Gurgle

Hellrazer wrote: »

My assumption is that only 1 year passes for earth aswell as myself.

Einstein's Theory of General* Relativity says that 2001 years pass on earth while one year passes for you, the 2000 years when you were travelling at the speed of light don't clock up for you.

This theory has been proved by generating short-lifetime particles at the speed of light and catching them further away than they could possibly have travelled through normal time before they decayed.

*Maybe it's Special relativity, I mixes them up.

Hellrazer

Gurgle wrote: »

Einstein's Theory of General* Relativity says that 2001 years pass on earth while one year passes for you, the 2000 years when you were travelling at the speed of light don't clock up for you.
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But youre travelling "instantly" not taking 2000 years to reach your destination according to an earlier post.

veXual

Hellrazer wrote: »

But youre travelling "instantly" not taking 2000 years to reach your destination according to an earlier post.

Thats my thinking aswell I don't really understand where this 2000 years is coming from.

Travelling at the speed of light is literally travelling at 300,000 mph or whatever to another destination?

Hellrazer

veXual wrote: »

Travelling at the speed of light is literally travelling at 300,000 mph or whatever to another destination?

Yup thats the way I read "light speed" aswell--hence my last few posts-I really dont understand this "instantaneous" appearing at your destination thing.


Say your destination is 1 light year away then it will take you 1 year to reach that destination travelling at "light speed" constantly.


Regardless of whether you experience the year or not it still takes a year to get there.

So is the instantaneous effect only for you the traveller but its still taken a year to get there--no?

narac

Hellrazer wrote: »

Can you explain how the 2001 years pass for earth when Im travelling instantly to my destination?
I leave Earth today 25/8/2009 and travel 1000 Light years "in an instant" according to narac`s earlier post.

I keep my own clock with me--so Im only using earth time because thats what my body is used to ie 365 days on a day/night cycle--Stick with me here.

So I arrive at my destination instantly on the 25/8/2009--I spend 1 earth year (only according to my clock) on the planet and return on 25/8/2010 again according to my clock.

No. You are misunderstanding what I am saying. From your perspective, you arrive 1000 lightyears away instantly. Time has stopped for you and you alone, because you are travelling at the speed of light. When you stop travelling and return to "normal" velocities, you return to the "normal" timeframe. So if you leave earth and travel 1000 lightyears at the speed of light, you will experience no time, and arrive instantly. But to us casual observers, you will have taken 1000 years to arrive at your destination, and another 1000 years to travel back to Earth.

Because the clock you brought with you is also travelling at the speed of light, it also experiences no time in the travelling. Therefore, according to your clock, you will be back on earth on 25/8/2010. However, according to all the clocks on Earth, the date will be 25/8/4010, because 2001 years will have passed for the Earth.

Hellrazer wrote: »

But youre travelling "instantly" not taking 2000 years to reach your destination according to an earlier post.

You are only travelling instantly from your point of view. For observers left on earth, you are travelling for 1000 years in each direction.

Gurgle wrote: »

Its worth pointing out that the whole sci-fi notion of travelling backwards in time is pure makey-uppey stuff.

It only works if you make two contradictary assumptions:

1) Relativity is correct, at the speed of light you need infinite energy to accelerate any further.

2) Its possible to accelerate beyond the speed of light

Not quite correct, from what I understand. It takes infinite energy to achieve light speed, not to accelerate beyond it. According to relativity (not sure which one either), the energy curve is symmetric about the speed of light. According to this, if you could accelerate beyond the speed of light, you would start losing energy.

Gurgle wrote: »

So why are these assumptions contradictory:
To accelerate is to increase your velocity. If you have mass, this means increasing your momentum.

This means adding energy. Generally, you can increase your momentum by adding a finite amount of energy, but at the speed of light you have to add that energy in zero time(because time has stopped).

Your power (energy per unit time) is x / 0 = infinity.

This makes sense. However, if you were travelling at the speed, it would also take infinite power to slow down to a sub-light speed. A force would need to be applied in the opposite direction to your travel, that force would need some amount of energy, and (because time has stopped for you) would also need to be applied in zero time, inferring infinite power required to slow down from lightspeed.

Hellrazer

narac wrote: »

No. You are misunderstanding what I am saying. From your perspective, you arrive 1000 lightyears away instantly. Time has stopped for you and you alone, because you are travelling at the speed of light. When you stop travelling and return to "normal" velocities, you return to the "normal" timeframe. So if you leave earth and travel 1000 lightyears at the speed of light, you will experience no time, and arrive instantly. But to us casual observers, you will have taken 1000 years to arrive at your destination, and another 1000 years to travel back to Earth.

Because the clock you brought with you is also travelling at the speed of light, it also experiences no time in the travelling. Therefore, according to your clock, you will be back on earth on 25/8/2010. However, according to all the clocks on Earth, the date will be 25/8/4010, because 2001 years will have passed for the Earth.

You are only travelling instantly from your point of view. For observers left on earth, you are travelling for 1000 years in each direction.

^^^^^^^^^Thats exactly what I was looking for.It was the whole instant travelling thing that had me.

I knew that one of my earlier posts was correct when I said that

I think its something to do with the fact that youre travelling so fast in relative to earth so that even though only 2 years have passed for you then earth has aged more--I hope someone corrects me on this because Ive been trying to remember where I read it or even if what I read is correct.

You threw me off with the arriving at your destination instantly thing.I thought you meant you literally arrived instantly and didnt take any "time" to get there.

Hellrazer

Great thread by the way and quite interesting.Its something Ive read up on(in a non-serious way) since I started collecting "The unexplained" way back in the 80s and it had a section on time travelling and blackholes and thier relationship to time travel.

Now that Ive understood those previous few posts heres a related question.

Light speed is supposedly constant--yes?? And that speed cannot be broken?

Now lets assume that it can be broken and you are travelling again.Lets use 1 light year since its easy to work with.

So if I travel at 2 x light speed will it only take me 6 months to get there or if Im not mistaken isnt there a theory that after you travel faster than light speed isnt "time" supposed to start to travel backwards-again assuming that time can travel in reverse?

So what happens in the theoretical example above?

veXual

A lightyear is defined as the distance light travels in a calendar year i.e. 10x13 kilometers per 365 days I believe.

So traveling for 1000 lightyears at the speed of light will just take 1000 calendar years no? If I were traveling at said speed I would notice the passage of 1000 years would I not?

I'm completely open to correction here tis just my view on it at the moment

Gurgle

narac wrote: »

This makes sense. However, if you were travelling at the speed, it would also take infinite power to slow down to a sub-light speed. A force would need to be applied in the opposite direction to your travel, that force would need some amount of energy, and (because time has stopped for you) would also need to be applied in zero time, inferring infinite power required to slow down from lightspeed.

Go backwards a bit - its actually impossible to reach the speed of light, but depending on your maximum power output its theoretically possible to get very very close.

When your velocity is nearly at the speed of light, time has nearly stopped and you would have to input a nearly infinite power (energy per relative second) to accelerate any closer to the speed of light.

At the speed of light, you can't do anything - you won't be looking out the window, checking your watch, pushing your foot down on the accelerator - nothing at all, because time has stopped.

Cutting it down to 3 dimensions, its an unreachable destination. In maths its an asymptote.

Hellrazer

veXual wrote: »

So traveling for 1000 lightyears at the speed of light will just take 1000 calendar years no? If I were traveling at said speed I would notice the passage of 1000 years would I not?

Exactly travelling 1000 light years at the speed of light will take 1000 years to an outside observer who is not travelling at the same speed.

And no you wouldnt notice the passage of time because at light speed time has stopped for you but for everyone else it continues as normal.So you jump into your ship and as soon as you hit light speed--time stops until you decelerate from light speed so for you the journey is instantaneous.

Gurgle

Hellrazer wrote: »

Light speed is supposedly constant--yes?? And that speed cannot be broken?

Sort of....
OK, because I haven't actually got a PhD in theoretical physics I'm gonna say Yes.

Hellrazer wrote: »

Now lets assume that it can be broken and you are travelling again.Lets use 1 light year since its easy to work with.

So if I travel at 2 x light speed will it only take me 6 months to get there

Erm, if you are willing to assume its been broken, then you've already written off the theory of Relativity. In that case, yeah - why not.

Hellrazer wrote: »

isnt there a theory that after you travel faster than light speed isnt "time" supposed to start to travel backwards-again assuming that time can travel in reverse?

Its not a physics theory as such, its a mathematical construct. Some mathematician(s) who couldn't follow the physics went trawling through the maths instead.

Hellrazer wrote: »

So what happens in the theoretical example above?

Einstein punches you in the nose and tells you to pay attention.

veXual

I'm not attempting to be ignorant but why does time stop for some one who is travelling at the speed of light?

Light travels at 300,000 km per second, so if I travel at lightspeed for one minute which is 18,000,000 km will I not just arrive 18,000,000 km away after 1 minute of travelling??

Gurgle

veXual wrote: »

I'm not attempting to be ignorant but why does time stop for some one who is travelling at the speed of light?

Light travels at 300,000 km per second, so if I travel at lightspeed for one minute which is 18,000,000 km will I not just arrive 18,000,000 km away after 1 minute of travelling??

In Newtonian physics, thats exactly what happens. It was almost 300 years from when Newton figured out all the mysteries of the universe until Einstein updated them.

If you travel at 60kmph for an hour, you experience an hour and you're 60km away.

Its only when you start getting to extremely high speeds (relativistic speeds) that Newton's answers stop working.

Hellrazer

Gurgle wrote: »

Sort of....


Erm, if you are willing to assume its been broken, then you've already written off the theory of Relativity. In that case, yeah - why not.

But in reality has any of these theories been 100% proven?

Einstein punches you in the nose and tells you to pay attention

Is this after they prove backwards time travel is possible :D

veXual

Ok I see what you are getting at. Once we begin to talk lightspeed we enter a whole other ballpark

Gurgle

Hellrazer wrote: »

But in reality has any of these theories been 100% proven?

To answer carefully, GR has been tested to the limits of modern technology and hasn't been proven incorrect.

The simplest test was the one with atomic clocks on airplanes (Hafele–Keating experiment, link)

Another (more head-melting) verification is muon-lifetime measurements.

To put it simply:
Muons are unstable elementary particles, they cease to exist after 2.2uS.
They can be generated in laboratories, with different velocities.
The ones launched fastest (closest to the speed of light) have been 'caught' at distances further from their source than they could possibly have travelled during their lifetime.

Sorry, I can't find a decent link which explains it better.

Hellrazer wrote: »

Is this after they prove backwards time travel is possible :D

:P

narac

Gurgle wrote: »

Go backwards a bit - its actually impossible to reach the speed of light, but depending on your maximum power output its theoretically possible to get very very close.

When your velocity is nearly at the speed of light, time has nearly stopped and you would have to input a nearly infinite power (energy per relative second) to accelerate any closer to the speed of light.

This is what I said. It takes infinite energy to reach the speed of light, not to go beyond the speed of light.

Gurgle wrote: »

Sort of....
OK, because I haven't actually got a PhD in theoretical physics I'm gonna say Yes.

Erm, if you are willing to assume its been broken, then you've already written off the theory of Relativity. In that case, yeah - why not.

Um, Einstein's theories don't preclude travel at twice the speed of light, or at any multiple of the speed of light. Ok, for us it is impossible to go faster than the speed of light, because to go faster than light, we would first need to go at the speed of light, which require infinite energy.

Gurgle wrote: »

Its not a physics theory as such, its a mathematical construct. Some mathematician(s) who couldn't follow the physics went trawling through the maths instead.

That's what all of physics is - mathematical constructs that describe the universe or aspects of the universe.

Excession

Hellrazer wrote: »

So you jump into your ship and as soon as you hit light speed--time stops until you decelerate from light speed so for you the journey is instantaneous.

Is this to say then that a person could never "experience" travelling at light speed? Once at this speed they could not look out a window or even be conscious that they are in fact travelling at this speed? They would only be conscious of accelerating and decelerating with time slowing down (for them) as they approach light speed?

Gurgle

narac wrote: »

Einstein's theories don't preclude travel at twice the speed of light, or at any multiple of the speed of light.

Its kinda down to the semantics - You can't accelerate to (and therefore past) the speed of light in normal space, but that doesn't neccessarily mean you can't get to somewhere faster.

e.g. wormholes
A wormhole may provide a shorter path between two points than normal space, and going through it may get you there faster than light would travel through normal space - but this is not time travel.

To an observer in normal space, you appear to have travelled faster than light but that doesn't break GR - in this case 'absolute' time applies, not relativity. You will not have travelled backwards.

That's what all of physics is - mathematical constructs that describe the universe or aspects of the universe.

Relativity describes spacetime physics at velocities from 0 to c, but to 'extend' the logic and conclude that beyond c time will go backwards has no basis in reality.

Hellrazer

Gurgle wrote: »

e.g. wormholes
A wormhole may provide a shorter path between two points than normal space, and going through it may get you there faster than light would travel through normal space - but this is not time travel.

These wormholes are called Einstein-rosen bridges?Again I remember reading up on these a while back and the theoretical possibility of building one using a "gravity tractor" I think it was called.Something about gathering enough mass in one place to collapse space into an artificial black hole on one side and on the other side of it is an artificial white hole.Could be used as a bridge between 2 distant points in space.

Interesting concept but could it ever be a possibility?

And also wondered since space and time are interlinked would the "bridge" not warp time aswell as space causing some sort of time distortion?

r3nu4l

Hellrazer wrote: »

Interesting concept but could it ever be a possibility?

This is what I wonder about as well. Is there any evidence thus far that wormholes might actually exist or is this all just mathematical speculation based on the fact that the maths says it could happen?