By Tuan Nguyen
Posting in Energy
Scientists show that a single photon in a vacuum cannot move faster than the speed of light.
“Life can only be understood backwards; but it must be lived forwards.” -- Søren Kierkegaard
The notion of traveling back in time to correct regrettable mistakes like misplacing your iPhone has long been the stuff of science fantasy. Sadly, to the chagrin of sci-fans everywhere, physicists in China now have evidence that suggests it will most likely stay that way.
It was only within the last 10 years that researchers have begun to postulate that time travel was even remotely possible when one experiment at Princeton University demonstrated the superluminal or faster-than-light transmission of optical pulses. It was at once both a startling and exciting finding considering that Albert Einstein's well-tested theory of relativity stipulates that the speed of light, which travels at 186,000 miles-per-second, acts as a de facto speed limit for everything in the universe. And since an object approaching such a speed would experience time slowing down to a crawl, exceeding it would conceivably allow the object to go backwards in time.
But the most stupefying part of all this was that, on a fundamental level, the idea itself violated the basic law of causality, wherein time, by nature, is built upon an ongoing chronological sequence events known as "cause and effect." I mean just imagine the sort of chaos that would ensue if someone traveled back to the past to prevent their own conception.
Alas, researchers at the Hong Kong University of Science and Technology had to render all this tantalizing hoopla moot by measuring the ultimate speed of a single photon in a vacuum and showing that it cannot move faster than the speed of light. This was achieved by passing a photon through a group of laser-cooled rubidium atoms.
"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," says lead author Shengwang Du.
The researchers also added that the test results "confirms Einstein's causality; that is, an effect cannot occur before its cause."
And as for the laser pulse experiment, scientists realized that it was merely a visual effect and that the superluminal 'group' velocity of many photons couldn't be used for transmitting any real data.
Coincidentally, the purpose of the study, published in the Journal Physical Review Letters, was not to investigate time travel but to advance the understanding of quantum data transmissions.
(via Press release)
Image: Back to the Future, Universal Pictures
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Jul 27, 2011
If time travel existed somebody, anybody.. should have witnessed someone from future till now.... if there are no such records of a person from a different time, then time travel atleast towards the past has never really happened! If nobody from future ever appeared till now...then nobody ever has time travelled in the future..!
Going back in time!!! despite all the so called development in science, too fundamental perceptions such as time, point, infinitesimal, infinity, dimensions are actually not understood. you can't imagine going back your imagination!
If going near the speed of light you have a penlight on forward can the power of that little light accumulate? Could cosmic rays actually be records of FTL flight? Dumb idea but if if FTL happens it will require immense amounts of power applied. Perhaps that would explain why they come from all sorts of directions and are not consistent sources. Just a little extra BS to throw into the mix. Have fun withe ideas. That';s where the furture comes from
As Einstein put it, spooky movements at a distance or something to that effect. Entanglement is why he was concerned since it would cause something faster than light speed to occur in a cause and effect relationship. Just guessing
Great subject and one of much speculation, thank you for sharing.... wanted to pass the following links along to any with an interest in this subject??? Time travel is impossible! Read Q& A in its entirety??? http://www.divineadvancedhumanbeings.com/answers/i-am-completely-off-topic-so-feel-free-not-to-answer-but-i-thought-i-might-as-well-ask-just-in-case-travelling-from-here-through-other-dimensions-typically-involves-leaving-the-space-time-continuu/ Also, you may be interested in the following article referencing time travel??? These advanced being-aliens are not from the future. Time travel for them and all beings, for that matter, is impossible regardless of the technology that they possess. Even God cannot time travel! http://www.divineadvancedhumanbeings.com/do-aliens-exist/
So, light (photons) can't travel faster than light. Now that's a really surprising conclusion. I wonder if Sound can travel faster than sound? Oh well. It's time to ask other questions. All of this will seem so silly in a few years.
However, we think we know what the limits are where we are, but there are lots of places in the universe where these "commonly" known laws don't apply. Think of a black hole. Does light move faster there or not. We do not know and cannot know until we do practical experiments. Some say that we would stretch out like spaghetti if we entered a black hole. But since black holes have a larger event horizon than a point, we may well survive the travel. After all, we are almost 100% empty space. Gravity is different than the boost of a rocket, because the rocket pushes You through a surface, Your skin on Your bottom (if You are sitting), but gravity pulls You at every point in Your body at the same time. As for breaking the laws of causality; if something gets changed then it was always that way, no matter how many times we change it.
http://www.laughparty.com/print.php?id=430 Anyway, the headline of the article is 'Is time travle possible?'. - my understanding is that every astronaut in effect time travels, just not backwards .... or am I mistaken?
this space and time. Maybe the rules can't be broken based on the space that you are in but what if space in the vacinity can be changed? If you change the space that you are in, could mean that to everyone else outside of your space you are breaking the rules? Maybe space can operate, under the right conditions, like you walking back and forth on a train going 60 mph (100 kph). Walk forward and you are observed, by someone outside of your space as going 63 mph. Walk back towards the end and you are observed going 57 mph. All the while you have not broken the rule that you can't walk faster than 3 mph. All we need to figure out what is the train when it comes to space.
The initial conditions of the Big Bang singularity determined the direction of time to be always into the future. To travel in time would mean exiting the event horizon of one universe and entering another. Because event horizons are moving in respect to each other. Navigation would be extremely interesting if not impossible. You would never find your way home. Not that it would matter, because you would have to exit our timeline via a singularity & that is not a survivable option.
I think the researchers at Hong Kong University of Science and Technology may be wrong. I recall reading in ScienceDaily of an experiment in which, under special conditions, a "packet" of light arrived at one end of the test device before it was released on the other side. Of course we're talking nano or pico level but there are speed limits only in Einsteinian space-time. Einstein refined our Newtonian space, why can't his be refined?
Even if this experiment is conclusive evidence of physical particles being limited to the speed of light (which it probably isn't), it tells us nothing of the possibility that consciousness itself may be able to travel to different times and places. What about quantum particles ~ aren't they supposed to exist in more than one place at a time? Similarly, perhaps they exist in more than one time at the same place too... "The researchers also added that the test results ???confirms Einstein???s causality; that is, an effect cannot occur before its cause.???" Travelling back in time doesn't necessarily mean defiance of Einstein's causality... beings/people may have already travelled back and there contributions/effects, if any, are already woven into te universe's tapestry. Or, perhaps it is only possible to travel back as an inconspicuous observer... One thing I've never understood is, even if one could go faster than the speed of light, why does that necessarily mean you are going back in time? Doesn't it just mean what you are looking at is not reflecting what is actually happening at that moment? When you slow down again, the light will catch up. Similar to having a delay in audio/video over the internet... just because there is a delay in hearing/seeing your friend talking, doesn't mean they actually are talking any later.
Throughout time there has been countless naysayers saying we can't do something in particular, like flying, using lasers or talking to someone on the other side of the world. Just because our feeble little minds can't figure it out yet don't mean it can't be done. Perhaps in a hundred years or so people will be looking back on this day and shaking their heads in disbelief in our inabilities like we look back on others a hundred years ago. I can still remember when they said "You can't fly faster than the speed of sound". Yeah....Right......
Photons might not be able to exceed C, but space itself does indeed, according to the standard model. How else could the universe be somewhere around 150 bly big and only 13 by old?
I went back in time to start it. But tomorrow I will go back and delete this, so if you are reading this it means you are in a doomed alternate timeline. Sucks to be you.
"single photons cannot travel faster than the speed of light" may be true but that does not indicate that there is 'nothing faster than the speed of light'.
The astronauts don't time travel. Their clock simply slows down relative to ours on Earth. If they reached the speed of light (c) their clock would stop (relative to us) but under no conditions would it ever run backward since c is the inviolable speed limit of the universe as we see it.
Tony, humans invented time thus there's a past, present and future. The Big Bang exists in our heads only; the human "laws of physics" can't explain the singularity. I agree with you on time travel. Somehow we would have to violate the laws of physics to do it.
The signal in the experiment you referred to didn't go backwards in time, it just appeared to move faster than the signal did in a vacuum, or in a fiber optic cable. the aparatus, if I recall correctly, involved a high magnetic field, with a high voltage between two parallel plates, separated by about a wavelength in a vacuum. The interpretation made at the time was that the plates and magnetic would, working together, suppress the creation and destruction of virtual particles, which is believed to occur in empty space all the time, at a small enough scale. If i remember correctly, the researcher (Russian, I think) calculated that the speed of light under these special circumstances was about 25% faster than in a vacuum. Richard Feynman is the one who equated faster than light travel with time travel. It may not turn out to be true. We really don't know enough to be able to say.
Actually, this experiment just proves that light can't go faster than light. All rest mass particles, like protons, neutrons, electrons, and you and me are limited to travel at slower than light speed. But, that is still in a local space. related to a viewpoint from very far away, we are in fact moving faster than light, right now. It all depends on how you look at it, and from where.
The space is not moving away from the center of the universe. Instead, the space itself is expanding. So the laws of physics prohibits objects from moving faster then light with respect to each other but there's no such constraint when the space between them is expanding. (If this doesn't make sense to you --> http://en.wikipedia.org/wiki/Observable_universe)
I don't have the answer, but the expansion of the universe could be a function of higher dimensions or the estimated life of the universe is way off. I read the announcements by scientists and wonder how they were able to focus on only 1 photon and measure its velocity. The earlier experiments alluded to in the article claimed to be able to slow or speed up photons. Without knowing the methodology and criteria, I am not able to say whether the results are valid or not. I like Steven Wright's question "If you are in your car travelling at the speed of light; if you turn your headlights on, do they do anything?"
Maybe the past is still there ? Maybe time just is. If time travel into the past and future is possible then where are the tourists ? If as I suspect, Our universe is only one of a myriad of globule universes extruded by the singulrity of a black hole from a previous Universe and expanding into a region of total entropy, I like to call the 'Big Nothing'. This starts to make sense, if we consider that a singularity is infinitely small, hot, and dense. Then we can presume that Infinities are the order of the day and it is a cycle of black hole singularity to black hole singularity. We humans are still very primitive. Our Homo sapien brains are only about 80,000 years young. Which is shorter than a blink of the eye in cosmic terms and we can't rap our heads arround infinities.
Thanks, YetAnotherBob. As you see, my comprehension of the experiment wasn't that great. And, isn't c a theoretical speed in NOTHING rather than the speed of light in a vacuum? (I've been reading Brian Cox's great books on making heady cosmological topics understandable for dummies like me).
You can never actually reach the speed of light. You can just get very close. To you in the car, you will see the headlights acting normally. To someone outside the car, it might be very different. But, they would have to look very quickly. Of course, your clock will be off by a lot when you do stop.
The other possible implication (besides time travel not being possible) is that humankind doesn't last long enough to develop it and our primitive selves just aren't that interesting to anybody else who did.
I think you're right about the past still being there. I still love the "space warp" concept of science fiction where you could "cut across" the curvature of space-time and, say, go back to Nov 22 1963 and observe what really happened in Dealy Plaza.
The energy required to accelerate any mass rizes exponentially. As the speed aproaches 'C' the increase in the effective mass becomes infinite. So to does the required energy. That is the simplest explanation. It require an infinite amount of energy to accelerate any mass to reach the speed of light This doesn't apply to expansion of space/time itself. So if we could safely cocoon ourselves in an electromagnetic bubble and compress the space/time in front of us while stretching it out behind us. There would be no limit to the effective speed. Of course navigation would be a bitch. The Einstein-Rosen bridge idea that is better known as wormholes, would work if you could stop them from collapsing into a singularity and crushing all of your atoms and sub atomic particles out of existance as soon as you entered the mouth. That is of course if you can find one.