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+4valhalla Bad Wolf Luky Nessa 8 posters | |
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Nessa Admin
Number of posts : 7028 Age : 111 Life : Points : Mood : Registration date : 2007-07-20
| Subject: Time Travel Possible? Tue Aug 21, 2007 12:19 pm | |
| First topic message reminder :A new concept for a time machine could possibly enable distant future generations to travel into the past, research now suggests.
Unlike past ideas for time machines, this new concept does not require exotic, theoretical forms of matter. Still, this new idea requires technology far more advanced than anything existing today, and major questions remain as to whether any time machine would ever prove stable enough to enable actual travel back in time.
Time machine researchers often investigate gravity, which essentially arises when matter bends space and time. Time travel research is based on bending space-time so far that time lines actually turn back on themselves to form a loop, technically known as a "closed time-like curve."
"We know that bending does happen all the time, but we want the bending to be strong enough and to take a special form where the lines of time make closed loops," said theoretical physicist Amos Ori at the Technion-Israel Institute of Technology in Haifa. "We are trying to find out if it is possible to manipulate space-time to develop in such a way."
Many scientists are skeptical as to whether or not time travel is possible. For instance, time machines often are thought to need an exotic form of matter with so-called "negative energy density." Such exotic matter has bizarre properties, including moving in the opposite direction of normal matter when pushed. Such matter could theoretically exist, but if it did, it might be present only in quantities too small for the construction of a time machine.
Ori's latest research suggests time machines are possible without exotic matter, eliminating a barrier to time travel. His work begins with a donut-shaped hole enveloped within a sphere of normal matter.
"We're talking about these closed loops of time, and the simplest kind of closed loops are circles, which is why we have this ring-shaped hole," Ori explained.
Inside this donut-shaped vacuum, space-time could get bent upon itself using focused gravitational fields to form a closed time-like curve. To go back in time, a traveler would race around inside the donut, going further back into the past with each lap.
"The machine is space-time itself," Ori said. "If we were to create an area with a warp like this in space that would enable time lines to close on themselves, it might enable future generations to return to visit our time."
Ori emphasized one significant limitation of this time machine—"it can't be used to travel to a time before the time machine was constructed." His findings are detailed in the Aug. 3 issue of the journal Physical Review D.
A number of obstacles remain, however. The gravitational fields required to make such a closed time-like curve would have to be very strong, "on the order of what you might find close to a black hole," Ori told LiveScience. "We don't have any way of creating such strong gravitational fields today, and we certainly have no way of manipulating any such gravitational fields."
Even if time machines were technically feasible, the gravitational fields involved need to be manipulated in very specific, accurate ways, and Ori said his calculations suggest any time machine could be very unstable, meaning "the tiniest deviations might keep one from working. We need to explore the problem of stability of time machines further."
Theoretical physicist Ken Olum of Tufts University in Medford, Mass., who did not participate in this study, was skeptical concerning how this new model claimed to sidestep prior theoretical objections to time travel.
Still, Olum noted, "It's important if it's right—that there really is some kind of loophole. So this should be scrutinized very closely." The point of such work, he added, was to "expand the bounds of what's possible, what kind of things we can have and what kinds of things we cannot have." | |
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mkerv Power Member
Number of posts : 364 Age : 50 Location : Central Jersey Points : Registration date : 2007-08-14
| Subject: Re: Time Travel Possible? Wed Jan 30, 2008 1:45 pm | |
| OK I found it...at the bottom of the artical I just posted.
Time travel to the future is clearly possible as it is in accordance with the laws of physics. Whether or not backward time travel is a possibility remains to be seen. Unfortunately for fans of time travel science fiction, most theories involving backward time travel only allow for time travel after the point at which the first time machine is created. Furthermore, the theories have holes in them that may never be resolved. For the time being, fans of time travel science fiction will have to content themselves with novels and with movies. | |
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| Subject: Re: Time Travel Possible? Wed Jan 30, 2008 2:11 pm | |
| Good article I'm not a physicist at heart but I still was able to follow, you'll have to give me the site where you got this lil tasty |
| | | mkerv Power Member
Number of posts : 364 Age : 50 Location : Central Jersey Points : Registration date : 2007-08-14
| Subject: Re: Time Travel Possible? Wed Jan 30, 2008 4:55 pm | |
| I found it here. http://hubpages.com/hub/Time_travel_theory | |
| | | mkerv Power Member
Number of posts : 364 Age : 50 Location : Central Jersey Points : Registration date : 2007-08-14
| Subject: Re: Time Travel Possible? Tue Feb 05, 2008 8:06 am | |
| http://www.straightdope.com/columns/070511.html
Dear Cecil:
I read recently that "time . . . passes more quickly when gravity is reduced." Assuming gravity is reduced at higher altitudes, that means time goes by faster in Santa Fe than in Poughkeepsie. What's up with that? — Chris in SF, NM
Cecil replies:
You heard right, Chris. But unless you're way more anal than anybody I want living in my reference frame, you won't have to reset your watch. Due to the "warpage of time," clocks run slower in Poughkeepsie than Santa Fe by about a millisecond. Per century. (Get friendly with a black hole and it's another story — gravitational time dilation approaches infinity as you near the event horizon. However, notwithstanding sporadic distortions of space-time due to Taos, Los Alamos, Roswell, etc, we'll assume that's not a problem for you in New Mexico.) Time dilation affects not just ordinary clocks but any measure of time, including how long it takes to say "one Mississippi, two Mississippi." So you'll never notice anything odd about SF time, only about that of people living under different gravity conditions, e.g., Poughkeepsie, Hoboken, or other low burgs.
The effect was first hypothesized by Albert Einstein in 1907 as a consequence of his "happiest thought," the equivalence principle, which says gravity is locally indistinguishable from acceleration. Think of an elevator — as it accelerates you upward, you're squashed to the floor, which feels like an increase in gravity. That's no trick of the senses, says Einstein. Experiments performed over short range and brief time can't differentiate between acceleration and gravity. Originally just a cool idea, the EP and its consequences, including gravitational time dilation, have since been thoroughly confirmed.
It's probably not obvious to you why the EP results in time dilation, and I'll admit steam was rising off the diodes by the time I got the whole thing processed. But let's give it a shot:
1. Imagine you're in a spaceship far from any source of gravity. The ship is moving in a straight line at constant speed, so you float in the center of the cabin. Now imagine your idiot brother at the controls unexpectedly turns on the rocket booster, accelerating the ship. The rapidly approaching back wall is now indistinguishable from a floor you're falling toward under gravity.
2. Now consider a light source on this "floor" that emits a photon (light particle) of a certain frequency. Because the speed of light is finite, it takes time (albeit very little) to make the trip to the "ceiling." By that time, the light receiver, along with the rest of the ship, has slightly increased its speed due to the ship's acceleration. The ceiling receiver (at the moment of reception) is always moving a bit faster than the floor emitter was (at the time of emission), even though the distance between them never changes. This invokes the Doppler effect, more familiar to us in sonic form: because of the aforesaid speed difference, the receiver will record the photon's frequency on arrival as slightly lower than it was on departure from the emitter.
3. Frequency, whether of clock ticks, pendulum swings, or photon pulsations, is a basic measure of time — a second officially is the time it takes for certain photons emitted by cesium-133 atoms to vibrate 9,192,631,770 times. If you and I measure the frequency of a given photon differently, we'll measure the flow of time differently too. So if I'm on the ceiling when the photon arrives, I time its vibrations and say, woo, that pup is slow. Meanwhile, an observer on the floor will say, nah, your stopwatch is fast.
4. Likewise, since the EP tells us acceleration = gravity, and gravity decreases with elevation above sea level (the "floor"), you in your mountain fastness will say sea-level time runs slow, while I in my shoreline cabana will say mountain time runs fast.
Anyway, that's the theory. Does it really work that way? You bet. Einstein used general relativity (which is bound up with gravitational time dilation) to explain a known oddity in Mercury's orbit. More recent experiments involved atomic clocks on jet flights. Here both gravity- and speed-dependent special relativity effects must be taken into account. After a westward around-the-world jet flight, flying clocks gained 273 nanoseconds, of which about two-thirds was gravitational.
Mere nanoseconds, you say — who gives a flying clock? You do, if you use the global positioning system. Because of their altitude, the clocks on GPS satellites run about 30 nanoseconds fast per minute due to gravitational effects. Since the system works by timing light signals and the distances involved are great, an uncorrected time error would mean a distance error growing at about 9.5 meters per minute. You may think it's amazing you can hike in the Sangre de Cristos with a $300 GPS receiver that tells you exactly where you are. What's more amazing is that the geniuses who designed it needed a rough knowledge of general relativity to get it to work.
—CECIL ADAMS | |
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