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Jay
23 Feb 06,, 01:44
The textbooks say nothing can travel faster than light, not even light itself. New experiments show that this is no longer true, raising questions about the maximum speed at which we can send information.

Can a light pulse travel faster than the speed of light? This question has intrigued physicists for many years because such an event could violate Einstein's theory of special relativity and the principle of causality (that 'cause' always precedes 'effect'). Together these imply that no object or information can travel faster than the speed of light, c=3times108 m s-1. For nearly two decades, physicists have been sending certain light pulses faster than c over short distances (so-called superluminal propagation), but the light pulses have always been distorted in the process so interpreting these experiments has been difficult1-3.

In May this year, Mugnai et al.4 reported superluminal behaviour in the propagation of microwaves (centimetre wavelengths) over much longer distances (tens of centimetres) at a speed 7% faster than c. A report by Wang et al.5 ( page 277 of this issue) now demonstrates a very large superluminal effect for pulses of visible light, in which a pulse propagates in a specially prepared medium with a negative velocity of -c/310: that is, not only faster than a pulse travelling in a vacuum, but so fast that the peak of the pulse exits the medium before it enters it!

A negative velocity can be understood by comparing the times it would take for identical pulses of light to cover some distance L in a vacuum (travelling at velocity c) and in a superluminal medium (travelling at velocity v). The difference in transit times DeltaT= L/v-L/c is a negative quantity if the velocity is superluminal. If v has a negative value then DeltaT can become sufficiently negative that the peak of the pulse emerges from the medium at an instant earlier than when the peak of the pulse enters. This brings to mind Arthur Buller's well-known limerick with relativistic over tones:

There was a young lady named Bright,
Whose speed was far faster than light;
She set out one day,
In a relative way,
And returned home the previous night.

But Wang et al.5 claim that, unlike the heroine of this rhyme, their light pulses do not violate causality. They argue that their superluminal pulses are the result of the wave nature of light itself (fortunately, making it impossible for an object with mass to travel faster than c) and that no actual information, or signal, is transmitted faster than c. They use smooth, well-defined light pulses, so that the peak of the pulse at the output results from the forward rising edge of the input pulse, which occurs far earlier in time, making it consistent with causality. An abrupt feature in the light pulse would not be able to travel faster than c. This means that even if the 'effect' appears to precede the 'cause', you still can't send useful information such as news of an impending accident faster than c.

A light pulse has a finite duration, and it is a well-known theorem in physics (the bandwidth theorem) that, to create a pulse of finite duration, an infinite number of waves of different frequency must be added together. The shorter the desired pulse, the larger the bandwidth of frequencies that must be used. All light pulses are therefore formed by a packet of waves of different frequency, each of which has a different amplitude and phase. There is a distinction between the speed of individual waves, called the phase velocity, vp, and the velocity at which the peak of the wavepacket propagates, known as the group velocity, vg. In a vacuum the phase and group velocities are the same, but in a highly absorbing or dispersive medium they are usually different. A negative group velocity results when the phases of the different frequency components are shifted by the medium through which they travel, so that the wavepacket they form at the exit is brought forward in time compared with the same pulse travelling through a vacuum.

One way to achieve negative velocity is to modify the refractive index of the medium through which the light passes. Last year scientists at Harvard6 and elsewhere succeeded in modifying the refractive properties of a cloud of ultracold atoms to generate very slow light pulses with group velocities of a few metres per second. To create the opposite effect superluminal pulses of light you need a medium in which the refractive index changes rapidly, for example near an atomic absorption frequency ( Fig. 1a). The only problem is that the so-called anomalous dispersion region in Fig. 1a, where vg can be negative3, is also in a region where there is increased light absorption. In experiments with such highly absorbing materials, the light pulses are either strongly distorted or absorbed, making any faster-than-light claims difficult to interpret.

Figure 1 Sending photons faster than light. Full legend

High resolution image and legend (95k)

A more promising approach to making superluminal light pulses is to work with an atomic medium where there is gain (amplification of light waves) at the atomic transition frequency. This is achieved in a laser-type medium by creating a 'population inversion', whereby a higher population of atoms are in the excited than in the lower-energy atomic state7. In this case, anomalous dispersion occurs at frequencies lower than the transition frequency. But close to the transition frequency, where the effect is largest, the rapidly changing gradient in the refractive index causes severe pulse distortion. One way round this problem is to use a gain doublet8 that is, two closely spaced regions of gain where the zone between has steep anomalous dispersion but without strong pulse distortion (Fig. 1b). This is what Wang et al.5 have now achieved.

The experiment by Wang and co-workers creates this type of gain doublet in a six-centimetre cell containing caesium gas by using two laser fields closely spaced in frequency (see Fig. 1a on page 277). They first measured the refractive index of the caesium using a third 'probe' laser, and produced a dispersion curve similar to Fig. 1b, with a steep gradient in the anomalous dispersion region corresponding to an expected vg= - c/310. When they sent a 3.7-microsecond light pulse through the medium, it appeared at the exit of the cell before it arrived at the entrance. Although the pulse itself is only shifted forward in time by a modest fraction (1.7%) of its width, this corresponds to the wavepacket leaving the cell 62 nanoseconds before it arrives in other words, travelling nearly 20 metres away from the cell before the incoming pulse enters it. Compared with the time to travel six centimetres in a vacuum (about 0.2 nanoseconds), the 62-nanosecond lead means that the group velocity of the pulse inside the medium is - c/310, close to the predicted value.

In this experiment, each of the different frequency components making up the pulse experiences a slightly different dispersion in the medium. The relative phases between them are therefore changed and the pulse shape is shifted to bring the pulse wavepacket (or group velocity) forward in time. So the anomalous dispersion leads to interference between different frequency components of the pulse that produce the superluminal effect. Although amazing, this type of superluminal pulse propagation does not violate the principle of causality.

There remains, however, some debate about what is the true speed at which information is carried by a light pulse. Traditionally the signal velocity of a light pulse is defined as the speed at which the half peak-intensity point on the rising edge of the waveform travels; in this experiment, this is clearly superluminal. In contrast, some researchers argue that the true speed at which information is carried by a light pulse is not the group velocity of a smooth pulse, but rather the speed at which a sudden step-like feature in the waveform travels, which so far has not been shown to exceed c. Superluminal effects are especially interesting in the case of light pulses consisting of only a few photons, in which it could be argued that the group velocity is the same as the velocity of the individual photons. The type of superluminal behaviour discussed here is also predicted to apply to single photons8, which might have implications for the transmission of quantum information.

1. Steinberg, A. M. , Kwiat, P. G. & Chiao, R. Y. Phys. Rev. Lett. 71, 708 711 (1993). | Article | PubMed | ISI | ChemPort |
2. Balcou, Ph. & Dutriax, L. Phys. Rev. Lett. 78, 851854 (1997). | Article | ISI | ChemPort |
3. Chu, S. & Wong, S. Phys. Rev. Lett. 48, 738741 (1982). | Article | ISI | ChemPort |
4. Mugnai, D. , Ranfagni, A. & Ruggeri, R. Phys. Rev. Lett. 84, 4830 4833 (2000). | Article | PubMed | ISI | ChemPort |
5. Wang, L. J. , Kuzmich, A. & Dogariu, A. Nature 406, 277 279 (2000). | Article | PubMed | ISI | ChemPort |
6. Hau, L. V. , Harris, S. E. , Dutton, Z. & Behroozi, C. H. Nature 397, 594598 ( 1999). | Article | ISI | ChemPort |
7. Chiao, R. Y. Phys. Rev. A 48, R34R38 (1993). | Article | PubMed | ISI | ChemPort |
8. Steinberg, A. M. & Chiao, R. Y. Phys. Rev. A 49, 20712075 ( 1994). | Article | PubMed | ISI |

http://www.nature.com/nature/journal/v406/n6793/fig_tab/406243a0_F1.html
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v406/n6793/full/406243a0_fs.html

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Werent we discussing about universe and travelling faster than light some time?? :)

omon
06 Jun 07,, 21:11
according to this article, something does move faster than light.

Over the course of latter decades, tens of unexplainable microscopic and macroscopic effects in natural sciences and especially in physics and biology have been revealed and investigated. It should be emphasized that a large part of these phenomena were demonstrated by objects having spin or angular momentum.

Probably the first researcher who experimentally detected the unusual effects associated with torsion was a professor of the Russian physical-chemical society, N.P.Myshkin, who at the end of the nineteenth century conducted a series of experiments using scales [1]. These experiments were successfully repeated in the 1960s by professor N.A.Kozyrev and V.V.Nasonov and later by V.S.Belyaev, S.P.Mikhailov, A.G.Parkhomov and others.

In the 1940s, the soviet astrophysicist N.A.Kozyrev proposed that the rotation of stars was connected with their energy output. According to the theory developed by N.A.Kozyrev, time and rotation are closely interconnected. In order to verify his theory, N.A.Kozyrev conducted a series of experiments with spinning gyroscopes. The goal of these experiments was to make a measurement of the forces arising while the gyroscope was spinning. N.A.Kozyrev detected that the weight of the spinning gyroscope changes slightly depending on the angular velocity and the direction of rotation. The effect he discovered was not large, but the nature of the arising forces could not be explained by existing theories. N.A.Kozyrev explained the observed effect as being the manifestation of some "physical properties of time" [2,3].

In the 1970s, in order to verify N.A.Kozyrev's theory, a major research of gyroscopes and gyroscopic systems was conducted by a member of Belarus Academy of Sciences, professor A.I.Veinik. The effect discovered earlier by N.A.Kozyrev was completely confirmed, but in order to explain the observed results, A.I.Veinik developed his own theory. According to this theory, every substance has it's own "chronal charge" defined by the quantity of "chronal" particles which were named "chronons". A.I.Veinik supposed that while the object is spinning, "chronons" are interacting with other "chronons" that surround this object and therefor the weight of the object changes. According to A.I.Veinik's theory, "chronons" generate the so called "chronal" field. A.I.Veinik found experimentally that strong "chronal" fields can be generated by spinning masses. A.I.Veinik measured some properties of "chronal" fields and found that two types of "chronons" exist ("plus" and "minus" chronons). It is important to emphasize that A.I.Veinik concluded that the sign of the "chronon" depended on orientation of it's spin [4].

Reported observations of gyroscope weight variations have been made repeatedly by various researchers in many countries (e.g.[5-7]). Almost in all cases the observed effects were interpreted as the manifestation of antigravitation. In 1989, H.Hayasaka and S.Takeuchi conducted a series of experiments in which the fall-time of a freely-falling spinning gyroscope was measured. They found that the fall-time varied depending on the angular velocity and the direction of rotation. H.Hayasaka and S.Takeuchi have attempted to explain the effect of antigravitation as the manifestation of torsion fields generated by the spinning gyroscope [6].

It should be noted that reports stating that the weight of a spinning gyroscope does not change are also known. Analysis of these reports shows that experimenters have simply not fulfilled the conditions required to achieve the expected effect. N.A.Kozyrev, A.I.Veinik and other researchers who obsered the change of weight emphasized repeatedly that the rotation must be non-stationary. For instance, N.A.Kozyrev and A.I.Veinik used special vibrations, and H.Hayasaka experimented with moving (falling) gyroscopes.

From the mid-50s to the late 70s, professor N.A.Kozyrev (with V.V.Nasonov) conducted astronomical observations using a receiving system of a new type. When the telescope was directed at a certain star, the detector (designed by N.A.Kozyrev and V.V.Nasonov) positioned within the telescope registered the incoming signal even if the main mirror of the telescope was shielded by metal screens. This fact indicated that electromagnetic waves (light) had some component that could not be shielded by metal screens. When the telescope was directed not at the visible but at the true position of a star, the detector then registered an incoming signal that was much stronger. The registration of the true positions of different stars could be interpreted only as registration of star radiation that had velocities billions of times greater than the speed of light. N.A.Kozyrev also found that the detector registered an incoming signal when the telescope was directed at a position symmetrical to the visible position of a star relative to it's true position. This fact was interpreted as a detection of the future positions of stars [8].

In the late 1980s to early 90s, astronomical observations using the Kozyrev-type detector were successfully conducted by a group of academics at the Russian Academy of Sciences under M.M.Lavrentiev. While the sky was scanned by the shielded telescope with the detector inside, it registered signals coming from the visible position of each star, the true position, and also the position symmetrical to the visible position of a star relative to it's true position. M.M.Lavrentiev could not give a theoretical interpretation to these facts [9-11]. In 1992 these experiments were successfully repeated by the group of A.E.Akimov at the Main astronomical observatory of the Ukraine Academy of Sciences (Kiev,) and at the Crimean astrophysical observatory (Nauchnyi). The obtained results were interpreted as registration of torsion waves. (As is well known, stars are objects with large angular momentum.) [12,13].

In the course of the latter 50 years there have been numerous reports on anomalous behaviour of spin-polarized particles. In the USSR the groups under V.G.Baryshevsky and M.I.Podgoretsky experimentally determined that when neutrons are passing through spin-polarized targets, a precession of neutrons arises. The measured magnitude of precession has shown that the field which caused that precession has to be thousands of times stronger than the magnetic field of the target's nuclei [14]. In the USA the A.D.Krisch group repeatedly observed anomalies produced by spin-polarized protons [15]. In France, in experiments with 3He, it was found that the heat-conduction of helium unusually depends on the state of nuclei spins [16]. (This list can be easily continued.)

In 1977, A.C.Tam and W.Happer experimentally discovered that two parallel circularly polarized laser beams mutually attract or repel depending on mutual orientation of their circular polarization [17].

In 1966 the K.N.Perebeynos group demonstrated an experimental communication system in which the transmitter and the receiver were constructed as rotating masses. Transmitted information could be recieved even when the receiver was shielded by massive screens. The method applied was interpreted as the generation and reception of gravitational waves [18].

In spite of the seeming diversity, all of the experiments considered above have a certain resemblance: all of the mentioned effects are demonstrated by objects with spin or angular momentum. As was already noted, probably the first experimenter who made a major investigation of effects demonstrated by spinning objects was N.A.Kozyrev. It is also necessary to note A.I.Veinik's research work. A.I.Veinik made tens of types of generators based on rotating masses. These generators could change their weight (Very slightly. If a mass ~1 kg is rotating with the angular velocity ~ 20.000 rpm then the "inner force" ~30*10 -5 N.), and their "chronal" fields could affect practically all physical and biological objects and could not be shielded by "usual" screens [4]. It is also useful to note V.M.Yurovitsky's patented generators which are based on spinning magnets. V.M.Yurovitsky was the first who pointed out that many phenomena could be explained as a result of manifestation of long-range fields generated by spin or angular momentum density. Later generators based on mechanically rotating magnets were developed by V.V.Bobyr and many others. As a result of a series of experiments conducted in the Institute of Material Research ("Institut problem materialovedeniya" in russian) (Kiev, Ukraine) it was established that the emanation produced by this sort of generator is able to change the inner structure of any substance (it's spin structure). It was also established that an identical change of the structure of various substances can be achieved by "sensitives" ("psychics,") and could not be achieved by the use of other known technologies. The emanations of the developed generators was interpreted as torsion radiation [19].

In other series of experiments conducted in the Institute of Material Research, the influence of the torsion radiation on various photographs was investigated. It was established that by the use of this method it is possible to transmit information from one point of space to another [20]. (Probably the first researchers to apply this method were Albert Abrams, Curtis Upton, William Knuth, and George De La Warr.) The experimental research conducted in the Institute of Material research and at other scientific organizations was managed by the Center of non-conventional technologies under the USSR Science and Technics State Committee. These investigations were based on the so called "Theory of physical vacuum" developed by russian physicist G.I.Shipov.

G.I.Shipov used a geometry of absolute parallelism (A 4 ) with an additional 6 rotational coordinates, and on the strict level it showed that the movement of any object should be described by 10 movement equations but not by 4 equations as it is in Einstein's GR. From Shipov's vacuum equations, every known fundumental physical equation (Einstein's, Young-Mills', Heisenberg's, etc.) can be deduced in completely geometrised form. G.I.Shipov showed that besides the two known long-range physical fields - electromagnetic and gravitational - there exists third long-range field possessing significantly richer properties: the torsion field. The torsion field is an extremely unusual entity. First of all, the upper limit for the speed of torsion waves is estimated to be not less than 109 c, where c is the speed of light. Secondly, torsion fields are able to propagate in a region of space which is not limited by the light cone. That means that torsion fielda are able to propagate not only in the future but in the past as well. Thirdly, torsion fields transmit information without transmitting energy. Fourth - torsion fields are not required to follow the superposition principle [21].

Torsion fields are generated by spin (considering classical spin [22,23]) or by angular momentum. There exist both right and left torsion fields (depending on the spin orientation). Since all substances (except amorphous materials) have their own stereochemistry which determines not only the location of atoms in molecules but also determines their mutual spin orientation, then the superposition of torsion fields generated by the atomic and nuclear spins of each molecule determines the intensity of torsion field in the space surrounding each molecule. The superposition of all these torsion fields determines the intensity and spatial configuration of the characterist torsion field of that substance. Thus each substance possess its own characteristic torsion field.

The property which is open to influence by torsion fields is spin. (We should note that the spin-torsion interaction constant is equal to 10 -5 - 10 -6. This constant is less than the constant of electromagnetic interactions, yet much greater than the constant of gravitational interactions.) Thus the structure of the torsion field of every object can be changed by the influence of an external torsion field. As a result of such an influence, the new configuration of the torsion field will be fixed as a metastable state (as a polarized state) and will remain intact even after the source of the external torsion field is moved to another area of space. Thus torsion fields of certain spatial configuration can be "recorded" on any physical or biological object.

Since every permanent magnet possess not only oriented magnetic moments but also classical spins orientation as well, then every permanent magnet possess it's own torsion field. (This fact was first experimentally discovered by A.I.Veinik.) Understanding this important property of magnetic fields allows us to understand a variety of phenomena, for instance the phenomenon known as "magnetization of water".

The following fundamentally important fact should be emphasized. In the framework of the theory of electro-torsion interactions, it is shown that if electrostatic or electromagnetic fields exist in some region of space, then there always exists torsion fields in that region of space. Electrostatic or electromagnetic fields without a torsion component do not exist. On the strict level this is shown by G.I.Shipov [24]. Strong torsion fields are generated by high electrical potentials and by devices with organized circular or spiral electromagnetic processes. (Probably the first researcher to investigate torsion fields by this type of generators was Nikola Tesla. In Russia, similar results were obtained by S.V.Avramenko and others.)

Torsion fields can be generated as the result of the distortion of geometry of pthe hysical vacuum. Every object with a certain surface geometry will simultaneously generate left and right torsion fields of a certain configuration depending on the geometry of the object. This fact can be detected by various types of physical, chemical and biological indicators. This type of manifestation of the torsion field was repeatedly observed by numerous researchers: A.I.Veinik, Yu.V.Tszyan Kanchzhen, A.A.Beridze-Stakhovsky, V.S.Grebennikov, I.M.Shakhparonov and many others in Russia and various researchers in other countries [25-31]. Later an experimental investigation of the torsion fields generated by objects with different geometry of surface was conducted by the group of A.E.Akimov at the Physics Institute of the Ukraine Academy of Sciences and at Chernovitsky University [32].

Another kind of torsion generator employs a combination of the above described principles. For instance, the combination of high-frequency electromagnetic oscillations and topological effect ("form effect") is used in the generators developed by Yu.V.Tszyan Kanchzhen. The combination of high electric potential and topological effect is used in the device made by A.I.Veinik and in the device described in the patent [27]. The combination of magnetic fields and high-frequency electromagnetic oscillations is used in W.Kroppa's patented generators. Rotating magnetic fields are used in V.M.Yurovitsky's patented generators.

The extremely unusual properties and possibilities demonstrated by torsion field generators allowed the development of new approaches to the interpretation of various phenomena, including ESP and PK. From the late 80s till the late 90s, major experimental investigations were conducted that confirmed the theoretical predictions. It was established that torsion generators allow us not only to replicate all "phenomena" demonstrated by so called "psychics," but they also are able to demonstrate effects that were never demonstrated by any "psychic".

doc3 (http://amasci.com/freenrg/tors/tors3.html)

Shamus
06 Jun 07,, 23:06
Beam me up Scotty,me head's spinnin':confused: :biggrin:

glyn
06 Jun 07,, 23:41
20 or 30 years ago the BBC showed a studio demonstration where people could pick up weighty objects that were rapidly rotating (a mass at the end of a pole) which they could not lift when rotation was not taking place. But what does it all mean? Is it just a curiosity, or has it a useful application?

RustyBattleship
07 Jun 07,, 07:12
[QUOTE=omon;379676]something does move faster than light.[QUOTE]

Yes. My wife when Kohls is having its 60% off sale.

gunnut
07 Jun 07,, 08:03
Question: if nothing can travel faster than light, then how does a blackhole work?

The gravitational acceleration of a blackhole exceeds the speed of light, that's why light cannot escape the pull of the blackhole's gravity.

Of course conventional wisdom doesn't work beyond 30% of the speed of light. We have to ditch mechanics and move to relativity at that speed.

dave lukins
07 Jun 07,, 09:13
Beam me up Scotty,me head's spinnin':confused: :biggrin:

Don it's simple..listen..Light is always propagated in empty space with a definite velocity c which is independent of the state of motion of the emitting body. In other words light moves at the same rate irrespective of any movement to the observer..299,460km per hour..Got it now??:eek: :biggrin:

dave lukins
07 Jun 07,, 09:29
Question: if nothing can travel faster than light, then how does a blackhole work

As a Star starts to collape its gravitational field at the surface becomes stronger and the escape velocity increases. The escape velocity increases to 300.000kps. the velocity of light. After that time any light emitted from the Star would not be able to escape and would be dragged back by its own gravitational field..As special Theory of Relativity says "nothing can travel faster than the speed of light" so if its light cannot escape, nothing else can. the result..A black hole

gunnut
07 Jun 07,, 09:50
As a Star starts to collape its gravitational field at the surface becomes stronger and the escape velocity increases. The escape velocity increases to 300.000kps. the velocity of light. After that time any light emitted from the Star would not be able to escape and would be dragged back by its own gravitational field..As special Theory of Relativity says "nothing can travel faster than the speed of light" so if its light cannot escape, nothing else can. the result..A black hole

My question is are these photons stationary? Or are they falling back into the singularity? If they fall back, that means the acceleration of the gravitational field exceeds that of the speed of light, which is not possible under our current scientific understanding. If the escape velocity is exactly the speed of light, that means there are photons sitting stationary inside the event horizon.

I'm sure something is amiss here. I'm probably using mechanics to explain relativity...:rolleyes:

dave lukins
07 Jun 07,, 10:55
If the escape velocity is exactly the speed of light, that means there are photons sitting stationary inside the event horizon.

The boundary of the black hole is the Event Horizon..the light front that just fails to escape to infinity and remains in the Schwarzchild radius. It is thought that time stands still at the edge of a Black Hole, therefore Photons must be stationary. Even Einstein found the concept of black holes bizarre and refused to except they existed

BD1
07 Jun 07,, 12:24
It is the most ridiculous statement that the highest speed is the speed of light . Speed of darkness exceeds it definately , because everywhere the light reaches darkness is already there .:)

dave lukins
07 Jun 07,, 13:08
It is the most ridiculous statement that the highest speed is the speed of light . Speed of darkness exceeds it definately , because everywhere the light reaches darkness is already there .:)

Did'nt God say "let there be Light" can't recall Him sayin' let there be Dark!! unless He was talking about Coors!!:biggrin:

BD1
07 Jun 07,, 13:11
Well, this proves my point : darkness was already there . Faster . Again.

Officer of Engineers
07 Jun 07,, 17:03
Actually we don't know what's waiting for light. The universe is expanding and what's beyond it (ie, before the big bang) is unknown.

dave lukins
07 Jun 07,, 17:25
Actually we don't know what's waiting for light. The universe is expanding and what's beyond it (ie, before the big bang) is unknown.

How many "Big Bangs" have there been? Are we Sure there has been only the one?;)

Officer of Engineers
07 Jun 07,, 17:48
We're sure of the only one that we know of.

joey
07 Jun 07,, 20:29
Speedier than light is Mind ;)

Big bang et al has many controversies sorrounding that as well anyways.

highsea
08 Jun 07,, 23:24
...I'm sure something is amiss here. I'm probably using mechanics to explain relativity...:rolleyes:Yep. The photons are traveling in a straight line- it's the space that's curved.

gunnut
09 Jun 07,, 04:10
Yep. The photons are traveling in a straight line- it's the space that's curved.

That's right!!! Totally forgot about that. I assumed space to be straight rather than curved.

If we can find a way to warp space, we can develop some kind of .... warp engine, that can propel a ship to travel faster than light...;)

dave lukins
10 Jun 07,, 08:59
That's right!!! Totally forgot about that. I assumed space to be straight rather than curved.

If we can find a way to warp space, we can develop some kind of .... warp engine, that can propel a ship to travel faster than light...;)

Nice concept Gun' , however the simple act of sending the Machine into Space creates warp. It's the weight of the object that creates the "curve" in Space. So, from the most massive Stars to the speck of dust it all goes into creating the curvature of Space. Even Einstein thought time travel could be possible in both directions....So start building!!:)

entropy
11 Jun 07,, 12:25
Nice concept Gun' , however the simple act of sending the Machine into Space creates warp. It's the weight of the object that creates the "curve" in Space. So, from the most massive Stars to the speck of dust it all goes into creating the curvature of Space. Even Einstein thought time travel could be possible in both directions....So start building!!:)

Einstein thought that time did not really have a direction, as the other three dimensions also lack. But it was a series of coincidences who made it look like it did. Like if one is driving on a highway, without seeing the opposite direction driveway due to heavy rain, and assuming that all motion goes your way.

ArmchairGeneral
11 Jun 07,, 23:19
If they fall back, that means the acceleration of the gravitational field exceeds that of the speed of light, which is not possible under our current scientific understanding. If the escape velocity is exactly the speed of light, that means there are photons sitting stationary inside the event horizon.



Ummm...acceleration is not the same as velocity. :confused:

omon
11 Jun 07,, 23:45
Ummm...acceleration is not the same as velocity. :confused:

ummm, interesting point, i always thought acceleration is increase in velocity.
isn,t it?

glyn
11 Jun 07,, 23:58
ummm, interesting point, i always thought acceleration is increase in velocity.
isn,t it?

I think technically in physics that acceleration is 'a change in direction or rate'. So it should be theoretically possible to accelerate to a halt!
However the OED says it is taken from the Latin ac (add to) celer (swift) and they state 'motion increased in velocity'.

glyn
12 Jun 07,, 00:03
Ummm...acceleration is not the same as velocity. :confused:

Again the OED obliges.From Latin = velecitas, defined in English as 'Rapidity or celerity of motion'.

gunnut
12 Jun 07,, 05:05
Ummm...acceleration is not the same as velocity. :confused:

Well, the velocity of photon is 3*10^8 m/s

The gravitational acceleration of a black hole has to be greater than -3*10^8 m/s/s in order to stop light from leaving.

Earth's gravitational acceleration is 9.8 m/s/s, therefore, light can escape earth.

Again, this is a very linear thinking. When speed exceeds 30% of the speed of light, we have to ditch mechanics and use relativity to explain motion.

highsea
12 Jun 07,, 16:23
The gravitational acceleration of a black hole has to be greater than -3*10^8 m/s/s in order to stop light from leaving.
Photons are massless, and are not affected by gravity.

It's the SPACE that's curved. Light always travels in straight lines. (technically space-time geodesics)

joey
12 Jun 07,, 20:58
acceleration is rate of change of velocity (v-u)/t while velocity is rate of change of speed, speed is a scalar quantity while velocity is vector quantity.

Indeed photons, phonons are massless.

omon
12 Jun 07,, 21:06
i,m not so sure about that, according to this article light creates pressure, can someting with no mass create pressure?


Scientists have figured out how to create a jet of liquid with nothing but the power of light.

They shined a laser beam through a soapy liquid, producing a long jet that eventually broke up into droplets.

"I thought this was just so weird because I know when liquid is supposed to break up, and this one isn't doing it," said study team member Wendy Zhang, an assistant professor in physics at the University of Chicago.

In the image (right), the white bar at the bottom represents the width of a human hair. Credit: Regis Wunenburger and Jean-Pierre Delville

The work, done in cooperation with French scientists at the University of Bordeaux I, is detailed in the March 30 issue of the journal Physical Review Letters.

"In previous work, people figured out that you can move individual particles with lasers," said Robert Schroll, graduate student in physics at the University of Chicago and lead author of the journal article. Now it appears that lasers can also be used to generate bulk flow in fluids. "As far as we know, we're the first to show this particular effect."

Physicists know that the heat of lasers can move liquid. But this test found that the light itself, not heat, did the pushing.

"Light is actually pushing onto us slightly. This effect is called radiation pressure," Zhang said.

This gentle pressure generated by photons-particles of light-ordinarily goes unnoticed. But the liquid used in the new experiment-a soapy mixture-has such an incredibly weak surface that even light can deform it. It created a phase change that's a bit like how shampoo turns to soap when you add water, the scientists explained.

The newfound technique might offer a new way to control the flow of fluids through channels thinner than a human hair for biomedical and biotechnological applications, the researchers said.

Pressure of Light Can Move Liquid | LiveScience (http://www.livescience.com/technology/070327_laser_jet.html)

highsea
12 Jun 07,, 22:37
...can someting with no mass create pressure?It's not "pressure" in the Newtonian sense, it's electromagnetic radiation pressure. They are very different things that happen to have a common name.

ArmchairGeneral
12 Jun 07,, 22:40
Well, the velocity of photon is 3*10^8 m/s

The gravitational acceleration of a black hole has to be greater than -3*10^8 m/s/s in order to stop light from leaving.

Earth's gravitational acceleration is 9.8 m/s/s, therefore, light can escape earth.

Again, this is a very linear thinking. When speed exceeds 30% of the speed of light, we have to ditch mechanics and use relativity to explain motion.

Incorrect. Escape velocity is a lot more complicated than that. I'll be honest, I don't really understand how to calculate it, but I will point out that while Earth's gravitational acceleration is 9.8 m/s/s, escape velocity at the surface is approximately 11,200 m/s.

Helpful link: Escape velocity - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Escape_velocity)

ArmchairGeneral
12 Jun 07,, 22:42
I think technically in physics that acceleration is 'a change in direction or rate'. So it should be theoretically possible to accelerate to a halt!
However the OED says it is taken from the Latin ac (add to) celer (swift) and they state 'motion increased in velocity'.

That is correct. Negative acceleration (deceleration) is what you feel whenever you slow down.

ArmchairGeneral
12 Jun 07,, 22:47
Photons are massless, and are not affected by gravity.

It's the SPACE that's curved. Light always travels in straight lines. (technically space-time geodesics)

I'm no physics whiz, but I think you're making a unnecessary distinction between massy and massless objects. As I understand it, what we think of as a gravitational attraction is considered in relativity to be nothing more than the curvature of spacetime. Thus, everything that exists in spacetime, including photons, is affected by gravity.

dave lukins
12 Jun 07,, 22:54
Photons are massless, and are not affected by gravity.

It's the SPACE that's curved. Light always travels in straight lines. (technically space-time geodesics)

Measurements taken during an eclipse in 1919 showed that light from a distant Galaxy was bent by the mass of the Sun... that was in accordance with Einstein's law of gravitation

ArmchairGeneral
12 Jun 07,, 23:08
Measurements taken during an eclipse in 1919 showed that light from a distant Galaxy was bent by the mass of the Sun... that was in accordance with Einstein's law of gravitation

Technically, what was bent was space. Light was following the shortest path through space, which is by definition a straight line. A good analogy is seen in the flight paths of airplanes, which follow great circles (circles that bisect the Earth). On a Mercator projection, the path will look curved, but it's actually the shortest line between two points, and thus a straight line in spherical geometry.

dave lukins
12 Jun 07,, 23:30
Yes, in theory of general relativity, light would be bent by the deformation of the space-time continuum around an object such as a Planet

highsea
12 Jun 07,, 23:38
I'm no physics whiz, but I think you're making a unnecessary distinction between massy and massless objects. As I understand it, what we think of as a gravitational attraction is considered in relativity to be nothing more than the curvature of spacetime. Thus, everything that exists in spacetime, including photons, is affected by gravity.I was trying to point out that the description of photons being somehow accelerated by gravitational force is not the case. Photons do not "fall back" into a black hole, for example.

Photons are NOT affected by gravity. The space that they exist in IS. That is not an unnecessary distinction to physists, I can assure you. Gravity has absolutely no effect on a photon (or any other massless particle). If it did, photons could be sped up and slowed down, and the speed of light would not be a universal constant.

omon
13 Jun 07,, 00:21
It's not "pressure" in the Newtonian sense, it's electromagnetic radiation pressure. They are very different things that happen to have a common name.

oh, ok i see it makes sence now, is it like magnets have force or pressure, but flux itself(the force it self) has no weight, or does it?

ArmchairGeneral
13 Jun 07,, 03:35
I was trying to point out that the description of photons being somehow accelerated by gravitational force is not the case. Photons do not "fall back" into a black hole, for example.

Photons are NOT affected by gravity. The space that they exist in IS. That is not an unnecessary distinction to physists, I can assure you. Gravity has absolutely no effect on a photon (or any other massless particle). If it did, photons could be sped up and slowed down, and the speed of light would not be a universal constant.

But, if I understand correctly, in general relativity, there is no such thing as a gravitational force. What we think of as gravity is nothing more than an effect of curved space. Which is what affects photons, and everything else. So what's the difference between gravity (space-time curvature) affecting mass, and space-time curvature (gravity) affecting light?

gunnut
13 Jun 07,, 03:52
Incorrect. Escape velocity is a lot more complicated than that. I'll be honest, I don't really understand how to calculate it, but I will point out that while Earth's gravitational acceleration is 9.8 m/s, escape velocity at the surface is approximately 11,200 m/s.

Helpful link: Escape velocity - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Escape_velocity)

Ahh, but I did make the difference.

I stated the earth's gravitational acceleration is 9.8m/s/s

I never once said the earth's escape velocity is 9.8m/s

:biggrin:

gunnut
13 Jun 07,, 03:53
Photons are massless, and are not affected by gravity.

It's the SPACE that's curved. Light always travels in straight lines. (technically space-time geodesics)

OK, got it. That makes sense.

gunnut
13 Jun 07,, 03:55
Measurements taken during an eclipse in 1919 showed that light from a distant Galaxy was bent by the mass of the Sun... that was in accordance with Einstein's law of gravitation

Actually, light was not bent.

The space that light travels in was bent by the gravity of the star. So it "appears" that light was bent. But in reality light travels in a straight line, but if we curve the space, we can bent light.

ArmchairGeneral
13 Jun 07,, 04:04
Ahh, but I did make the difference.

I stated the earth's gravitational acceleration is 9.8m/s/s

I never once said the earth's escape velocity is 9.8m/s

:biggrin:

No, but you stated that since the escape velocity of a black hole must be at least 300 million m/s, the gravitational acceleration of a black hole must be at least negative 300 million m/s/s. Thus, by the same reasoning, since the escape velocity of the earth is 11,200 m/s, the gravitational acceleration must be 11,200 m/s/s. Which it ain't.

My apologies for leaving an /s on my previous post. :redface:

dave lukins
13 Jun 07,, 08:20
Actually, light was not bent.

if we curve the space, we can bent light.

So you ARE saying that light was bent:rolleyes: If not, I'm gonna wake Albert up and tell him he was wrong, and send him to your address:biggrin:

If you don't agree with "Bent" lets agree with the term "Deflected":) (for now)

dave lukins
13 Jun 07,, 08:40
No, but you stated that since the escape velocity of a black hole must be at least 300 million m/s,

For a Black Hole to stop emitting Light it has to shrink under its own gravity. As it shrinks the gravitational field at the surface becomes stronger and the escape velocity increases. By the time the Radius is down to 30km its escape velocity would have increased to 300,000 kps.. the velocity of light. After that, any light emitted by the star would not be able to escape to infinity and would be dragged back by the grav. field

gunnut
13 Jun 07,, 09:20
No, but you stated that since the escape velocity of a black hole must be at least 300 million m/s, the gravitational acceleration of a black hole must be at least negative 300 million m/s/s. Thus, by the same reasoning, since the escape velocity of the earth is 11,200 m/s, the gravitational acceleration must be 11,200 m/s/s. Which it ain't.

My apologies for leaving an /s on my previous post. :redface:

Good point. I guess I did infer that unintentionally.

gunnut
13 Jun 07,, 09:22
So you ARE saying that light was bent:rolleyes: If not, I'm gonna wake Albert up and tell him he was wrong, and send him to your address:biggrin:

If you don't agree with "Bent" lets agree with the term "Deflected":) (for now)

No, space was bent. Light was not bent. But the bent space with light traveling in a straight line appears to us as light bending.

I guess deflected is as good a term as any.