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Hong Kong scientists show time travel is impossible

54 Comments

Hong Kong physicists say they have proved that a single photon obeys Einstein's theory that nothing can travel faster than the speed of light -- demonstrating that outside science fiction, time travel is impossible.

The Hong Kong University of Science and Technology research team led by Du Shengwang said they had proved that a single photon, or unit of light, "obeys the traffic law of the universe."

"Einstein claimed that the speed of light was the traffic law of the universe or in simple language, nothing can travel faster than light," the university said on its website.

"Professor Du's study demonstrates that a single photon, the fundamental quanta of light, also obeys the traffic law of the universe just like classical EM (electromagnetic) waves."

The possibility of time travel was raised 10 years ago when scientists discovered superluminal -- or faster-than-light -- propagation of optical pulses in some specific medium, the team said.

It was later found to be a visual effect, but researchers thought it might still be possible for a single photon to exceed light speed.

Du, however, believed Einstein was right and determined to end the debate by measuring the ultimate speed of a single photon, which had not been done before.

"The study, which showed that single photons also obey the speed limit c, confirms Einstein's causality; that is, an effect cannot occur before its cause," the university said.

"By showing that single photons cannot travel faster than the speed of light, our results bring a closure to the debate on the true speed of information carried by a single photon," said Du, assistant professor of physics.

"Our findings will also likely have potential applications by giving scientists a better picture on the transmission of quantum information."

The team's study was published in the U.S. peer-reviewed scientific journal Physical Review Letters.

© 2011 Agence France-Presse

©2021 GPlusMedia Inc.

54 Comments
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That's why I always do my time travelling using tachyons.

1 ( +2 / -1 )

Guess professor Du has never watch any episodes of Star Trek, or has a understranding of what ludicrous speed is.

0 ( +1 / -1 )

Tell this to John Titor.

-3 ( +2 / -5 )

I've always had a fantasy about traveling in time to learn the potential winning lottery numbers, so this is very disappointing.

0 ( +1 / -1 )

"Nothing can travel faster than the speed of light"

Debatable. But even if that were true, what does that have to do with time travel?

ira-ira - I always do my time traveling using the slingshot effect :-0

-2 ( +0 / -2 )

Bummer. If this is proven, mankind will never leave the solar system. Are we really destined to remain marooned on an island (so to speak) for all eternity? Being an American frustrated with the seeming pull-back from space exploration, I would settle for Mars. Hell, I would settle for the Moon. However, the idea that space is our destiny is a powerful one; one that takes a real hit if we can never do better, no matter the tech, than light speed.

Just sayin....

-2 ( +0 / -2 )

Aren't subspace transmissions faster than light?

But I agree with the conclusion that time travel is impossible. If it was possible, we'd have people popping in from the past and the future all the time messing things up.

-2 ( +0 / -2 )

Sorry Mr Shengwang you're only looking at time in one way, time travel (to a degree) is most certainly possible, it is a clearly documented fact that satellite clocks in space run faster than those on earth and have to be adjusted all the time (http://en.wikipedia.org/wiki/Time_dilation). These satellites are theoretically in the future by a few seconds and every astronaut in the world are time travels to a certain extent by leaving earth.

He has ignored situations where black holes are involved and quantum mechanics.

This guy has been in a box or reading old books, there is a ton of new information out there, time travel has not been "thought up" in the last 10 years.

-2 ( +0 / -2 )

But even if that were true, what does that have to do with time travel?

Not sure, but you would appear to exist in multiple places at the same time which would be interesting.

-1 ( +0 / -1 )

Aren't subspace transmissions faster than light?

Are they even real? I thought that was from sci-fi haha!

-1 ( +0 / -1 )

they had proved that a single photon, or unit of light, "obeys the traffic law of the universe."

But did they try it out on a DeLorean? Or a police box?

Maybe they don't get Back to the Future or Dr. Who in China.

-1 ( +1 / -2 )

Don't want any Goobacks in here...

0 ( +1 / -1 )

He has ignored situations where black holes are involved and quantum mechanics.

This research is in the field of quantum mechanics, so I think it's safe to say they didn't ignore it.

0 ( +1 / -1 )

cleo: "But did they try it out on... a police box?

Ha ha ha! They didn't try it out in a phone booth either!

0 ( +1 / -1 )

yildirayJul. 26, 2011 - 01:50PM JST But even if that were true, what does that have to do with time travel? Not sure, but you would appear to exist in multiple places at the same time which would be interesting.

Actually they're demonstrated simultaneous existence in multiple places in quantum reactions (sub-atomic), and if something can simultaneously exist in two places then the speed of light becomes irrelevant, since the object does not "travel", but rather merely exists in two places simulatenously then ceases to exist in one and exists only in the other (i.e. it teleports). The interceding distance is not travelled at all. Time also seems to be different at a sub-atomic level, with time travel theoretically possible.

Therefore this experiment merely re-validates Einstein's theory of relativity, and does not preclude time travel using sub-atomic physics, although at the moment we lack the understanding to make sufficient sub-atomic particles act together in sufficiently large cohesive units in order to produce gross effects like teleporting a person or large object (although they are making progress in making groups of sub-atomic particles behave in the same or similar fashion).

In short, time travel may still be possible, but in all probability it would be prohibitively expensive in terms of the energy cost at this time.

0 ( +1 / -1 )

That's why I always do my time travelling using tachyons.

You should try using chronons. You get a much better effect if you can fine-tune your kit properly. But that's quite tricky and it does take a bit of time.

-1 ( +0 / -1 )

pawatan: No it isn't, Quantum Theory and Relativity Theory don't mix, Shengwang just "assumed" a bunch of varaibles and came to his own conclusion.

-1 ( +0 / -1 )

So we are stuck here on Earth then? Bummer..

I guess it is also difficult for alien races to visit us as well. Double bummer..

-1 ( +0 / -1 )

Professor Du’s study demonstrates that a single photon, the fundamental quanta of light, also obeys the traffic law of the universe

Light is made of photon's, he basically just said light is the speed of light.

ref:

Light, which is emitted and absorbed in tiny "packets" called photons

http://en.wikipedia.org/wiki/Light

-1 ( +0 / -1 )

Kronos: No it isn't with a warp drive (yes they are not just in Startrek they are theoretically possible) you can bend the space around the ship you are in without moving, expanding space behind a spaceship and shrinking it infront therefore not breaking the light speed barrier because the ship would not move, the space around it would move, which means you could get from point A to B very quickly over if you had to travel at light speed the same distance.

-1 ( +0 / -1 )

So they basically proved that light cannot travel faster than the speed of light.

As for Time Travel(Tm) , I travel trough time all the time at a nice close to constant pace which suits me just fine. Except for Monday mornings and Friday afternoons.

1 ( +2 / -1 )

Just when I was about to soup up my Delorean :(

0 ( +1 / -1 )

Serrano

Aren't subspace transmissions faster than light?

But I agree with the conclusion that time travel is impossible. If it was possible, we'd have people popping in from the past and the future all the time messing things up.

How do you know that they aren't popping in and messing things up?

-1 ( +0 / -1 )

Serrano

Aren't subspace transmissions faster than light?

But I agree with the conclusion that time travel is impossible. If it was possible, we'd have people popping in from the past and the future all the time messing things up.

How do you know that they aren't popping in and messing things up?

-1 ( +0 / -1 )

But what is the slowest you can go. can i move soooo slow that i travel through time or more clearly put: time passes me by. which would technically mean that i went back in time right. Has anyone every completely stopped anything?

-1 ( +0 / -1 )

They only discovered this now? they have come a long way..

-1 ( +0 / -1 )

Actually you can travel into the future and back into the past. I've done it and had my portable GPS device prove it. You see, I flew from Japan to California, having left Japan around 8am, crossed over the international dateline in the middle of the night having taken me a few hours into one day earlier. Then a few hours later I flew into the original day that I left. Not many people know this can be done or that it happens but it is true.

-3 ( +0 / -3 )

Oh yeah? Then how do they explain what happened in Star Trek IV: The Voyage Home?

-1 ( +0 / -1 )

They didn't try it out in a phone booth either!

I have, and it's overrated.

-2 ( +0 / -2 )

according to some, there may be numerous parallel universes that have " different " physical laws................what's impossible here may not hold true there.

0 ( +1 / -1 )

Perhaps Professor Du actually discovered that time travel is possible. This caused big problems though, with people killing their own great great grandparents, not to mention winning all the lottery jackpots.

To sort out the chaos, someone was sent back to amend the professor's research paper... to say that time travel was in fact impossible.

0 ( +1 / -1 )

oberts, I agree with you and since Jin2 I strongly believe in parallel worlds.

-1 ( +0 / -1 )

Don't worry; there are always wormholes.

0 ( +1 / -1 )

What? What about the flux capacitor? Didn't they try that?

-1 ( +0 / -1 )

Breaking news: Professor Du proves that light doesn't travel faster than light.

0 ( +1 / -1 )

For science, it is not cast in stone. It can be dis-proved and proved again and again.....

-1 ( +0 / -1 )

Time travel is easy. We all do it every minute of our lives and it has nothing to do with how fast photons are moving.

Ditto for travelling into the future. No photons are necessary. All you need to do is drop your temperature to absolute zero for the desired number of centuries, then bring yourself back up to normal temperature without incurring any of the cell damage normally associated with freezing human tissue. No aging and no electrical impulses at all when you're at absolute zero. Piece of cake. That revival bill is going to be a steep, though. I hope your investments while you were on ice panned-out.

-2 ( +0 / -2 )

JT - why is this story word-for-word the exact same story on Yahoo News?

Moderator: Because Yahoo News grabbed the story from AFP.

0 ( +1 / -1 )

Suppose that right now I traveled back 5 years to 2006, met my 2006 self and killed him. So the time travel never happened?

Also, if I traveled back in time and met myself, there would be two of us, right? Where did all the extra molecules come from?

-1 ( +0 / -1 )

Time travel may not be possible, but time surely stops in the meetings I have at work. ;-)

0 ( +1 / -1 )

So...just so I have a firm grasp of what is going on.....two scientists from Hong Kong proved that LIGHT does not travel faster than LIGHT...... That is pretty much what I have gotten out of this article.

0 ( +0 / -0 )

breaking the light speed barrier is impossible, but has nothing to do with other forms of time travel. Even if you could travel faster than light it would not be a very economical, viable or a safe method of doing so. The simplest and cheapest method is to setup your own starting point gateway today and leave it open. If in 10 years you feel the need to come back you can hop in to the current gateway which is connceted to the start gateway and go back 10 years. This is mainly achieved with lots of mirrors and lasers creating a vortex. Other methods to travel large distances can also be used to time travel like worm holes, black holes, multiple dimensions, loop effects, quantum jumps not to mention the speed of thought, but nobody has really even studied that yet. I would love to know what the speed of things like telepathy, instincts, intuition, dreams, love and so on are if one day calculable (I assume all things can be represented by NUMB3RS)

0 ( +0 / -0 )

So...just so I have a firm grasp of what is going on.....two scientists from Hong Kong proved that LIGHT does not travel faster than LIGHT...... That is pretty much what I have gotten out of this article.

I think what was really proven was that light always travels at its maximum speed and what we've been observing all this time is not its "casual cruise" speed. Can you imagine if the constant c turned out to NOT be a constant? The scientists would be relegated to the non-planet of Pluto for upsetting the theoretical physics world!

0 ( +0 / -0 )

Clearly the problem here was that they tested a single photon. Should have tested a married photon - then it would be more motivated to travel faster than the speed of light such that it could use time travel and travel back in time and walk away from the altar when he had the chance.

2 ( +2 / -0 )

Godan: Time travel may not be possible, but time surely stops in the meetings I have at work. ;-)

And that right there is an example of a profound similarity between your country and mine. 8-)

0 ( +0 / -0 )

Should have tested a married photon - then it would be more motivated to travel faster than the speed of light

I dunno. Those single photons get around.

0 ( +0 / -0 )

What else should a photon do than travel at the speed of light? Since it doesn't have mass, it doesn't have another choice. The experiment is referring to the difference between the speed light in the "wave picture" and in the "particle picture". In the "wave picture", You can have "phase velocities" which exceed the speed of light. However, the important thing is the "group velocity", which can never exceed the SOL. As the group velocity is the speed of the wave packet's information, it is more appropriate to think of SOL as information speed. And since one photon bears information just on its own (like its spin), it would have been a BIG miracle if it could run faster than light.

Still time travel is not ruled out yet. But if it is possible, You would need highly non-trivial configurations of space-time with holes inside. Imagine a donut. If space-time looked like this, then time-travel is still possible (in a thought experiment).

0 ( +0 / -0 )

My alien friends disagree with that theory!!!

My friend Chewbacca done it thousands of times.

You just need a power converter

0 ( +0 / -0 )

I dont believe it

I just came back from the space time continuum !!!

0 ( +0 / -0 )

why is it sometimes I know answers before I know the questions? deja vu

0 ( +0 / -0 )

It is impossible to travel faster than the speed of light, and certainly not desirable, as one's hat keeps blowing off.

Woody Allen

1 ( +1 / -0 )

demonstrating that outside science fiction, time travel is impossible.

This discovery doesn't demonstrate that time travel is impossible as traveling faster than light is not required. Just being able to approach the speed of light would allow one to travel far into the future by leaving Earth/returning. We time travel like this every time we fly in an airplane; we're just not going fast enough to notice.

0 ( +0 / -0 )

Serrano: Suppose that right now I traveled back 5 years to 2006, met my 2006 self and killed him. So the time travel never happened?

Alternate timelines and parallel universes maybe can explain the paradox?

0 ( +0 / -0 )

Serrano: Also, if I traveled back in time and met myself, there would be two of us, right? Where did all the extra molecules come from?

Easy answer. From the future!

0 ( +0 / -0 )

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