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[ShinNL]

everything in the universe is travelling through time right now.

Aaaaah. Aaaaah! Holy shit, so that's why it's called relativity :O! Universe suddenly makes sense (aside from the actual phenomenon).

 

[The Shadow]

So you guys are saying that time travel is a real thing? I thought that was never proven :O

Not time travel in the movie sense. The speed at which time passes can change though. An hour on earth and an hour on a starship traveling near the speed of light will seem the same to the people at either place. However, earth people will appear to be going in fast forward to the people on the starship and the people on the starship will appear to be moving extremely slow, or even stuck on pause to the people on earth.

They observe this effect because it quite literally is happening. Time is passing at different rates for them.

Aaaaah. Aaaaah! Holy shit, so that's why it's called relativity :O! Universe suddenly makes sense (aside from the actual phenomenon).

Exactly right.

 

[LaserBuddha]

Not time travel. The speed at which time passes can change though. An hour on earth and an hour on a starship traveling near the speed of light will seem the same to the people at either place. However, earth people will appear to be going in fast forward to the people on the starship and the people on the starship will appear to be moving extremely slow, or even stuck on pause.

They observe this effect because it quite literally is happening. Time is passing at different rates for them.

I read something about time slowing down slightly on fast jets or airliners or something. Like, they could actually witness the analog clock ticking every so slightly slower. True?

 

[The Shadow]

I read something about time slowing down slightly on fast jets or airliners or something. True?

Absolutely true. The effect is incredibly small because jets don't go anywhere near the speed of light, but they measured it with atomic clocks.

Edit:

Caught your edit. No, they wouldn't be able to see the difference because the actual time dilatation is very small because jets don't go very fast, relatively speaking. We're talking near speed of light starships here because that's when the effect becomes very noticeable and people look like they're frozen in time.

 

[ShinNL]

Not time travel. The speed at which time passes can change though. An hour on earth and an hour on a starship traveling near the speed of light will seem the same to the people at either place. However, earth people will appear to be going in fast forward to the people on the starship and the people on the starship will appear to be moving extremely slow, or even stuck on pause.

They observe this effect because it quite literally is happening. Time is passing at different rates for them.

Yeah, I always read it explained like this and I always dismissed it because I thought people were talking about the light rays hitting them later when a spaceship is flying away. So I was like: but if you fly back everything is back to normal. But apparently if you just move fast, even if you return, you're from a different time than where you came from. So fascinating D:

Thanks everyone

 

[mike23]

I read something about time slowing down slightly on fast jets or airliners or something. Like, they could actually witness the analog clock ticking every so slightly slower. True?

They wouldn't appear slower if they were on board the plane and you were viewing it from in the plane.

 

[LaserBuddha]

Okay so people in orbit travel slightly into the future. Is there anyway to amplify whatever effect causes this, and create useful forward time travel?

If that's even possible, it would take a ridiculous amount of energy I guess, but seems more obtainable than whatever other method.

 

[itxaka]

The clock flying near the speed of light is quite literally traveling slower in time. Atomic clocks on jets measure time slower than stationary atomic clocks. This has been tested and proven to be true time and time again.

As a matter of fact, the GPS satellites have to take in the time dilation effect because of their distance from earth and the speed at which they travel.

So arent The gps travelling in time then?

 

[C.Dark.DN]

So arent The gps travelling in time then?

yeah the clocks have to be corrected so things don't go bad down here

 

[Stinkles]

The speed of sound is the distance travelled during a unit of time by a sound wave propagating through an elastic medium. In dry air at 20 °C (68 °F), the speed of sound is 343.2 metres per second (1,126 ft/s). This is 1,236 kilometres per hour (768 mph), or about one kilometer in three seconds or approximately one mile in five seconds.

Without being overly simplistic, can't we assume the universe itself, that is, the fabric of space-time, is a real, elastic medium, and light is simply the most motile, speedy wave/particle within it? and that the energy required to push harder or faster against that fabric is related to C? And that the fabric is connected intrinsically to its total content, which would be constant. That at least poetically would explain why infinite energy was required to exceed it, because it would be one more joule than the total possible energy content of that fabric.

 

[The Shadow]

Okay so people in orbit travel slightly into the future. Is there anyway to amplify whatever effect causes this, and create useful forward time travel?

If that's even possible, it would take a ridiculous amount of energy I guess, but seems more obtainable than whatever other method.

So arent The gps travelling in time then?

Everything is traveling forward in time. GPS satellites are traveling slightly faster than we are because of the speed and distance from earth.


To magnify the effect, if you say, wanted to visit earth in a million years from now, you'd need to get near a large gravitational field (black hole) or travel near the speed of light for a time. Depending on the gravitational field or the speed at which you traveled, if you spent enough time there and returned, everything outside would have "aged" a million years.

 

[Slavik81]

So you guys are saying that time travel is a real thing? I thought that was never proven :O
(Alice is meeting an 'older' Bob)

Wikipedia has a section on experimental confirmation.

So arent The gps travelling in time then?

To you, they're travelling through time at a rate that is slightly faster than one second per second. To them, you're travelling through time at a rate that is slightly slower than one second per second.

Spoiler

Man, it gets confusing. You appear slower when you travel through time faster.

Either perspective is equally valid.

 

[LaserBuddha]

Is backwards time travel still considered impossible?

That's the only time travel that matters.

 

[itxaka]

Everything is traveling forward in time. GPS satellites are traveling slightly faster than we are because of the speed and distance from earth.


To magnify the effect, if you say, wanted to visit earth in a million years from now, you'd need to get near a large gravitational field (black hole) or travel near the speed of light for a time. Depending on the gravitational field or the speed at which you traveled, if you spent enough time there and returned, everything outside would have "aged" a million years.

So The fucking planet of The apes was right! We are doomed

So in The end The gps are manipulating The time thanks to their speed while we only...live with The normal speed?

 

[mrklaw]

That's not an easy explanation.

The train scene in Dumbo is an easy explanation.

As something gets faster, it gets heavier, as it gets heavier it gets harder to move. The closer you get to light speed the harder it is to have the power needed to push the increasing mass.

Done.

See, I always get confused at the 'as it gets faster it increases in mass'. Why?

 

[mike23]

Is backwards time travel still considered impossible?

That's the only time travel that matters.

Time travel into the future is the best, why would you want to go back to a time before technology? Take a hop for a day in a near light speed ship, loop around the solar system a bit and you're a thousand years in the future.


I think a pseudo backwards time travel could be possible if you stretch the definition a bit. I think that if you measure your speed relative to space itself and sit absolutely still, meaning 0c in any direction, then you would age quicker than everything else. So you could be a 80 year old in a year when you were only supposed to be 25. Time travel-ish. You aren't really crossing back over a time you lived, more like skipping the middle bit. Although, I have no idea if it would work that way, it seems like it should.

 

[Freshmaker]

Never mind.

 

[Korey]

So you can visit the future if you're going fast enough?

 

[Freshmaker]

So you can visit the future if you're going fast enough?

Yes. You're doing it now.

 

[ThoseDeafMutes]

Kind of defeats the purpose of traveling fast.

No it doesn't, because it works out that in order to travel 4 lightyears to Alpha Centari, it takes 4 years to an observer on Earth, but it may only take hours or days to the person on the spaceship.

 

[Slavik81]

Also, I read that a person on the space station will be ~4 seconds younger than they ought to be when they stay up there for a year. So they traveled 4 seconds into the future.

That's really the worst thing about traveling at near light speed. This website shows the time dilation effects at various speeds.

http://www.fourmilab.ch/cship/timedial.html

When you're going 0.999999999999999c, every day that passes on the ship 61286.634 years would pass by on earth. Kind of defeats the purpose of traveling fast.

The sequels to Enders Game handled this in a really cool way. In that universe there was faster-than-light communication, but space travel occurred at highly relativistic speeds.

So somebody could easily be a pen-pal, but if you wanted to visit them you'd have to deal with severe time dilation. For them 10+ years would pass as you made the trip, though it might only be a week or two for you.

The main character was constantly travelling, so he saw bits and pieces of different worlds over the course of thousands of years.

 

[dabig2]

Is backwards time travel still considered impossible?

That's the only time travel that matters.

Probably not, but it's fun thinking of ways to do it.

Here's a pretty fun program talking about time travel possibilities. Narrated by Morgan Freeman himself (the entire Through the Wormhole series is quite interesting and all episodes are up on youtube).

Through the Wormhole - Season 1, Episode 3: Is Time Travel Possible ?

 

[ThoseDeafMutes]

Without being overly simplistic, can't we assume the universe itself, that is, the fabric of space-time, is a real, elastic medium, and light is simply the most motile, speedy wave/particle within it? and that the energy required to push harder or faster against that fabric is related to C? And that the fabric is connected intrinsically to its total content, which would be constant. That at least poetically would explain why infinite energy was required to exceed it, because it would be one more joule than the total possible energy content of that fabric.

I dunno, maybe. That sounds similar to how pop science shows explain SR/GR (usually with a 2d plane), but I don't know whether that is actually accurate or not.

The sequels to Enders Game handled this in a really cool way. In that universe there was faster-than-light communication, but space travel occurred at highly relativistic speeds.

So somebody could easily be a pen-pal, but if you wanted to visit them you'd have to deal with severe time dilation. For them 10+ years would pass as you made the trip, though it might only be a week or two for you.

The main character was constantly travelling, so he saw bits and pieces of different worlds over the course of thousands of years.

AFAIK there are quite a few fictional 'verses that have FTL radio but no FTL travel. But if you were hoping for that in real life, you're out of luck, since FTL communication is every bit as bad as actual FTL travel for spaceships, in terms of causality violations.

 

[Trent Strong]

Consider this: the fact that there are laws of nature means something.

 

[ThoseDeafMutes]

Consider this: the fact that there are laws of nature means something.

If there weren't consistent physical rules, nothing could exist because nothing would have any rules governing it's behavior.

 

[mike23]

No it doesn't, because it works out that in order to travel 4 lightyears to Alpha Centari, it takes 4 years to an observer on Earth, but it may only take hours or days to the person on the spaceship.

Ahh, I was thinking that a 4 light year trip would feel like 4 years to the people on board and therefore many millennia to earth. Makes sense the other way around.

 

[LaserBuddha]

Time travel into the future is the best, why would you want to go back to a time before technology?

- Get some dinosaurs
- Put my dick in Raquel Welch's ass
- Kill Hitler and watch C&C Red Alert happen

 

[WAWAZA]

why do people assume human reason is truth?

 

[Korey]

Yes. You're doing it now.

Well, you know what I mean. If one day we have the tech to go super fast, that means there will be people that can literally visit like 200+ years in the future?

 

[KarmaCow]

See, I always get confused at the 'as it gets faster it increases in mass'. Why?

Replace mass with energy, they're basically the same thing. That's what e=mc^2 means, for the simple case of an object at rest.

Well, you know what I mean. If one day we have the tech to go super fast, that means there will be people that can literally visit like 200+ years in the future?

You're not visiting, you're living 200 years in the future. It's a one way trip forward. Functionally, it's more like being in stasis for 200+ years.

 

[ThoseDeafMutes]

- Get some dinosaurs
- Put my dick in Raquel Welch's ass
- Kill Hitler and watch C&C Red Alert happen

Twenty Fun Things To Do With A Time Machine

• Take half a critical mass of plutonium back to meet itself.
• Infest the timestream with time-beavers.
• Shoot the gunsmith.
• Take one end of a space-time wormhole and throw it into the other end.
• Release cloned Michael Crichtons into the Jurassic.
• Organise a mutual infanticide pact.
• Prevent this suggestion ever being made.
• Persuade Lewis Carroll to write "The Time Machine".
• Abduct your grandchildren and bring them up as your own kids.
• Plant a suicide note in JFK's pocket.
• Develop the temporal equivalent of waterskiing behind a speeding Tardis.
• Swap Adolf Hitler and Charlie Chaplin at birth.
• Genetically engineer yourself for maximum skill at genetic engineering.
• Go to Hiroshima, 06-Aug-45, and run amok with a chainsaw.
• Establish a Time Patrol Corps to prevent such frivolous tamperings with history (in 1897).
• Find whoever coined the phrase "Time Paradox" and hand them their own skull. Repeatedly.
• Simplify the controls on the average VCR remote by substituting chronoscopy for television.
• Steal Schrödinger's cat.
• Sell ten-year-old yogurt without contravening its "best before" date.
• Park your Time Machine on the Turin Shroud and travel backwards to see where it really came from.

 

[LaserBuddha]

why do people assume human reason is truth?

Because truth is relative, and human reason is the only relevant truth to humans.

 

[Slavik81]

Well, you know what I mean. If one day we have the tech to go super fast, that means there will be people that can literally visit like 200+ years in the future?

Sure, but it wouldn't be much different from being frozen in ice for 200+ years, then thawed. The end result would be more or less the same.

 

[mike23]

Well, you know what I mean. If one day we have the tech to go super fast, that means there will be people that can literally visit like 200+ years in the future?

It's not visiting so much as moving into the future at a lower "time cost" for yourself. You experience a day or two and everyone else experiences a longer period of time, depending on how close to light speed you travel at.

 

[ThoseDeafMutes]

Well, you know what I mean. If one day we have the tech to go super fast, that means there will be people that can literally visit like 200+ years in the future?

Uh huh, but they can never go back. It's a one way trip, just like normal living.

 

[Trent Strong]

If there weren't consistent physical rules, nothing could exist because nothing would have any rules governing it's behavior.

There could just be chaos. Subatomic particles randomly colliding with each other or something. I don't know why any laws would need to exist. (I realize that the universe is pretty chaotic as it is, what with space being mostly empty, exploding stars, galactic cannibalism and so forth.) The fact that we exist at all is pretty fucked. (No, I'm not saying 'God did it'. I'm an atheist.)

 

[Slavik81]

Twenty Fun Things To Do With A Time Machine
...

Wikipedia's rules of time travel from fiction is pretty entertaining.

 

[Always-honest]

Well, i was in a really long train once. The train had a length from Houston to Mars (in mid summer 1998).
The train was moving with the speed of light. I wasn't just sitting in that train though. I was on a motorcycle IN that train. And i was riding that motorcycle at the speed of light too.

So, calculator GAF, how many years untill i reach Jupiter?

 

[ThoseDeafMutes]

There could just be chaos. Subatomic particles randomly colliding with each other or something. I don't know why any laws would need to exist. (I realize that the universe is pretty chaotic as it is, what with space being mostly empty, exploding stars, galactic cannibalism and so forth.) The fact that we exist at all is pretty fucked. (No, I'm not saying 'God did it'. I'm an atheist.)

But particles only exist because physical laws make it so energy exists in certain forms. With no laws of physics this could not happen. Arguably energy, space and time only make sense within our physical universal construct too, so it's not very appropriate to imagine a universe with no rules, but that still has "stuff" in it.

Wikipedia's rules of time travel from fiction is pretty entertaining.

My list came from:

The SF Guide to Chronophysics, which is awesome and you should all read.

Well, i was in a really long train once. The train had a length from Houston to Mars (in mid summer 1998).
The train was moving with the speed of light. I wasn't just sitting in that train though. I was on a motorcycle IN that train. And i was riding that motorcycle at the speed of light too.

So, calculator GAF, how many years untill i reach Jupiter?

Like, zero bro. At light speed it would only take you minutes to get there, not taking into account time dilation. You wouldn't even have time to blink from your perspective, going that speed.

 

[Dilly]

There is a great explanation of this in Stephen Hawking's Universe, but I can't find it on youtube.

Anyway, it's a must watch for anyone interested in this stuff.

 

[Dreams-Visions]

why do people assume human reason is truth?

We don't. We assume human reason can lead to intelligent ideas that we can test...and the sum total of all the tests (whether it takes days, weeks, months, years, decades, centuries, or Milena for said tests to run their course) lead us to truth.

It's worked fairly well so far.

Got something better to go by?

 

[Freshmaker]

The sequels to Enders Game handled this in a really cool way. In that universe there was faster-than-light communication, but space travel occurred at highly relativistic speeds.

So somebody could easily be a pen-pal, but if you wanted to visit them you'd have to deal with severe time dilation. For them 10+ years would pass as you made the trip, though it might only be a week or two for you.

The main character was constantly travelling, so he saw bits and pieces of different worlds over the course of thousands of years.

Then they found they could travel FTL by imaging themselves in a new place. But only a space spider could remember an object in enough detail for it to be viable...

 

[CorkyFromLifeGoesOn]

That's kind of disappointing...

also inevitable

why we still got wormholes?

 

[HappyBivouac]

That is not even close to a satisfying explanation. Read the whole thing. It never once explains why the speed of light through space is the fastest possible speed. It just gives a really long-winded explanation for why there is a maximum possible speed through space, and then ends by saying "and that speed is the speed of light." It does not say why. Why are photons so important?

Everything in the article makes sense, but they never explain how this connects to light.

 

[szaromir]

I didn't bother to read the explanation (I read quite a few textbooks), but the limit of velocity isn't something you understand, it's something you assume (it's an axiom assumed to be true until proven false). Now, the general framework of relativity (which works around that axiom) is something you might understand and is quite intuitive actually.

 

[ThoseDeafMutes]

That is not even close to a satisfying explanation. Read the whole thing. It never once explains why the speed of light through space is the fastest possible speed. It just gives a really long-winded explanation for why there is a maximum possible speed through space, and then ends by saying "and that speed is the speed of light." It does not say why. Why are photons so important?

Photons go at the maximum speed because they are massless. We call it lightspeed because light was the first thing we measured that went at that speed.

 

[HappyBivouac]

Photons go at the maximum speed because they are massless. We call it lightspeed because light was the first thing we measured that went at that speed.

And this is why I think an explanation regarding mass and velocity actually works as an explanation. This article feels like a half explanation.

 

[szaromir]

Photons go at the maximum speed because they are massless. We call it lightspeed because light was the first thing we measured that went at that speed.

Correction - photons are the only things we measured that have go at the velocity of light. Gluons or gravitrons were never observed directly.

And this is why I think an explanation regarding mass and velocity actually works as an explanation. This article feels like a half explanation.

Nope. The explanation is a result of the axiom that the speed of light is the limit, therefore cannot be a sufficient explantation. If there was no limit, mass particles could increase in velocity infinitely as they would always have finite momentum.

 

[nomis]

Yes. You're doing it now.

No, he's visiting the present.

 

[Feep]

Quick question:

Earlier in this thread, it was noted that light, or more specifically, photons, are the only things we've directly observed in the universe to travel at the speed of light, because they are massless particles.

But if photons are massless, why are they affected by gravity in the first place? I know they *are* affected (gravitational lensing), but if the equation is GM1M2 / r^2, why is there any force at all?

Does it have to do with the fact that GM1M2 / r^2 is a low-energy approximation? Or do photons actually have mass? I also remember reading that a bunch of photons hitting a giant solar sail would actually exert a mild force, which implies mass as well.