Time travel possible?

veXual · 25-08-2009 3:31pm

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 · 25-08-2009 3:38pm

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 · 25-08-2009 3:42pm

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 · 25-08-2009 3:55pm

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

Gurgle · 25-08-2009 4:12pm

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 · 25-08-2009 4:40pm

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 · 25-08-2009 5:01pm

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 · 26-08-2009 9:19am

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 · 26-08-2009 9:33am

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 · 26-08-2009 10:01am

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?

Gurgle · 26-08-2009 10:17am

Hellrazer wrote: »

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?

Theres all kinds of notions about how to make a wormhole, mostly involving exotic matter, condensed matter, white holes, black holes... basically they're all based on hypothetical solutions (read: guesses) to stuff we don't understand.

On the other hand, in a sense 'Galactic Lensing' is a natural implementation of a wormhole - Basically when a galaxy moves between two points, they are closer together through that galaxy (due to the effect of its mass on spacetime curvature) than they are when it isn't there.

This also gives an indication of just how much mass would have to be simulated / assembled by the gravity tractor / black hole / condensed matter to implement a wormhole.

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

Yes, in the sense that the connected ends of the wormhole could be moving forward in 'absolute' time at different rates.

There is still no real physical theory that would allow backwards time travel.

ladyofthelake · 28-08-2009 1:44am

Very simple, the closer that you get to the speed of light, the more time slows down for YOU, the rest of the time stream passes at the normal rate. So, if you were to travel for only a few years at light speed and left the earth, when you came back while you would only be a few years older, perhaps millions of years would have passed here on earth.

Messed up but true.

Helix · 31-08-2009 5:59am

Hellrazer wrote: »

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

cant remember where i read it, but isnt it considered that the constants we take as constants arent actually constants, and some have been proven to have changed in the last few billion years

not sure if the speed of light is one of them, ill try to remember which of my books its in

Gurgle · 31-08-2009 8:58am

Helix wrote: »

cant remember where i read it, but isnt it considered that the constants we take as constants arent actually constants, and some have been proven to have changed in the last few billion years

Its more semantics than anything else - light speed is constant because a meter is defined as the distance light travels through a vacuum in 1 / 299,792,458 seconds.

Light speed doesn't change as our universe (or localized big bang debris field) expands, the speed of time doesn't change as that would make the maths ridiculous so the meter is what changes.

Turtwig · 31-08-2009 2:55pm

Gurgle wrote: »

Its more semantics than anything else - light speed is constant because a meter is defined as the distance light travels through a vacuum in 1 / 299,792,458 seconds.

Light speed doesn't change as our universe (or localized big bang debris field) expands, the speed of time doesn't change as that would make the maths ridiculous so the meter is what changes.

Actually it isn't just semantics..

Linky,

Note : Not for the Layman, unless they're brave:P

20goto10 · 31-08-2009 4:17pm

It is possible to see into the past. Light from distant stars takes so long to reach the earth that what we are seeing occured millions and billions of years ago. There is also a theory that suggests that the universe is donut shaped (I've no link, just google it), meaning that light eventually travels back around on itself. What this means, if proven, is that one of those stars out there is actually light from our sun from billions of years ago. In theory, we could one day have telescopic images of prehistoric earth in much the same way as we have images of the early universe.

It's quite easy to think well if we can see into the past then why can we not just travel to where the light is coming from? The problem is the past doesn't physically exist anymore. It's changed and all thats left is its photons whizzing around the universe.

It's still pretty cool to be able to see into the past though.

JoeB- · 13-10-2009 8:52pm

I don't think subjective time slows down at when you're travelling at the speed of light, or close to the speed of light.
The idea that when travelling at the speed of light you arrive anywhere instantly is just wrong...

Subjective time never changes... so everything will feel the same to you regardless of the speed you're travelling at.. this is the whole point, there is no way to determine the speed at which you're travelling, i.e if you're on a train, are you moving or is the Earth moving past you?, both viewpoints are correct.

So travelling at 99.9999% the speed of light, everything seems normal to you... you breathe normally, and age normally... it's when you stop and look around that you see many years have passed for those not speeding around.

Light takes eight minutes to get from the sun.. so if you travelled to the sn and back at 99.999999 % the speed of light it would take 16 minutes or thereabouts.. however 20 days or more may have passed on Earth.

Even if travelling at 99.9999999 % the speed of light certain parts of the universe would be too far away to reach.. this is why light from the earliest stages of the universe is still travelling towards us, it hasn't had a chance to get here yet.

Time travel may be physically possible, however the chances of humans ever doing it seem slim.

Some particles in accelerators have lived up to 2,000 times longer than they normally would.. this is when they are travelling so fast that in a second, where light has travelled 300,000km, the particle would only be behind the light wave by a few meters.. so that's very very fast.

komodosp · 27-10-2009 11:08am

Light takes eight minutes to get from the sun.. so if you travelled to the sn and back at 99.999999 % the speed of light it would take 16 minutes or thereabouts.. however 20 days or more may have passed on Earth.

No that's the wrong way around. If you went to the sun and back it would feel instantaneous to you, but to everyone on Earth, 16 minutes would have passed.

Here's a question though:

Time travels fast for someone standing still but slowly for someone moving fast. BUT. Speed is all relative isn't it? So how does "the universe" know that it is not the person on Earth moving fast and the person on the spaceship moving slow? i.e. that it should be the person on Earth aging slowly and the person in the spaceship aging normally?

maninasia · 09-11-2009 2:43pm

Time is relative and the perception of time depends on the observer, in the above case both of the observers are right at the same time.
Einstein realised this and this allowed him to develop his theory of relativity.

The universe does not have a conception of time, humans have a conception of time as a by-product of entropy, or the trend to disorder. If entropy was reversed we would also have a sense of 'time', but this time would be running backwards. We would think this is perfectly normal also if we were born into this universe.

To give an idea of time being a human construct what if we were an artificial intelligent entitry capable of copying ourselves infinitely in any medium, where does time begin and time stop? What if we were capable of creating new universes, what is time then?

Azelfafage · 19-11-2009 7:01pm

Amalgam wrote: »

Is it true astronauts on the space shuttle lose or gain a tiny tiny amount of 'time', relative to people on Earth?

It certainly is true.

The Apollo astronauts are owed 300 microseconds overtime by NASA for 40 years now.

See:

http://www.time.com/time/magazine/article/0,9171,839785,00.html

.

aDeener · 20-11-2009 1:44am

Delorean?

Time travel possible?

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