# The Naked Scientists Forum

### Author Topic: Does light curves space and time?  (Read 14041 times)

#### CPT ArkAngel

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##### Does light curves space and time?
« on: 26/08/2010 05:55:16 »
Does light curves space and time?

#### graham.d

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##### Does light curves space and time?
« Reply #1 on: 26/08/2010 08:40:04 »
I think the answer is yes, but not a lot! The total energy density in the universe must include a contribution from the energy from photons and therefore must contribute to the possible closure (or not) of the universe. The energy density of light is very small compared with matter; you could say light is light :-)

#### LeeE

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##### Does light curves space and time?
« Reply #2 on: 26/08/2010 16:21:22 »
An interesting question.

I don't think light will curve, or bend space-time, at least in just one dimension, thus changing a straight path to a curved one, for if it did then light would follow a curved path in 'free' space and nothing would actually be where it appeared to be.

Also, there's the issue of what direction the curvature was expressed.  For example, if the light were to curve to the left, then why should this be so, and why shouldn't it curve to the right instead, there being no obvious reason for a bias either way?

If light were to curve space-time then, it would make more sense to me for it to curve space-time in all directions, which we could imagine as curving both left and right simultaneously.  If this were the case though, then we wouldn't see a net curvature in direction because the sum of the curvature in all directions would effectively cancel out, leaving us with 'straight' space-time again, at least in terms of direction.  However, if the curvature was in all directions it would amount to a changing of the size of space-time i.e. if light curved space-time both left and right then that space-time would get bigger or smaller depending on whether the curvature diverged or converged.

Personally, I think it's possible, or even probable, that the passage of light through space-time will have some effect upon it, but rather than curving it or changing its size at right-angles to the direction that the light is travelling in, as would be the case if space-time were to be curved by the passage of the light, I would suspect that space-time might be compressed in the direction that the light is travelling i.e. more like a longitudinal wave rather than a transverse wave.

#### tommya300

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##### Does light curves space and time?
« Reply #3 on: 26/08/2010 17:46:09 »
oh my word, no it is their-zz [B)]
According to Einstein's General Theory of Relativity, matter bends the fabric of space and time. The distortion of the space-time continuum even affects the behavior of light…”

Gravity as Curved Spacetime
Einstein eventually identified the property of spacetime which is responsible for gravity as its curvature. Space and time in Einstein's universe are no longer flat (as implicitly assumed by Newton) but can pushed and pulled, stretched and warped by matter. Gravity feels strongest where spacetime is most curved, and it vanishes where spacetime is flat. This is the core of Einstein's theory of general relativity, which is often summed up in words as follows: "matter tells spacetime how to curve, and curved spacetime tells matter how to move". A standard way to illustrate this idea is to place a bowling ball (representing a massive object such as the sun) onto a stretched rubber sheet (representing spacetime). If a marble is placed onto the rubber sheet, it will roll toward the bowling ball, and may even be put into "orbit" around the bowling ball. This occurs, not because the smaller mass is "attracted" by a force emanating from the larger one, but because it is traveling along a surface which has been deformed by the presence of the larger mass. In the same way gravitation in Einstein's theory arises not as a force propagating through spacetime, but rather as a feature of spacetime itself. According to Einstein, your weight on earth is due to the fact that your body is traveling through warped spacetime!”

http://einstein.stanford.edu/SPACETIME/spacetime2.html
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#### LeeE

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##### Does light curves space and time?
« Reply #4 on: 26/08/2010 23:38:24 »
Umm... I think we're a bit ahead of you there, tommya300, insofar as we all know about mass distorting space-time, but the OP's question was about the effect of massless particles on space-time.

Also, space-time can be flat in a non-zero gravitational field i.e. not 'vanished', provided that all of the gravitational forces are perfectly balanced.

Finally, I'm afraid that the light paths in that diagram you included aren't quite correct, as they seem to show deviations away from the mass as they enter and then exit the gravity well.

#### tommya300

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##### Does light curves space and time?
« Reply #5 on: 27/08/2010 02:40:36 »
Umm... I think we're a bit ahead of you there, tommya300, insofar as we all know about mass distorting space-time, but the OP's question was about the effect of massless particles on space-time.
OK I see sorry.

Quote
Also, space-time can be flat in a non-zero gravitational field i.e. not 'vanished', provided that all of the gravitational forces are perfectly balanced.
Does this info have any creditability? Isn't  stanford.edu from Stanford University?

Quote
Finally, I'm afraid that the light paths in that diagram you included aren't quite correct, as they seem to show deviations away from the mass as they enter and then exit the gravity well.

At a glance at that diagram I would agree.
Look closer the mass is shown to be above the gravity well grid lines as the light path is below the mass following the grid lines.
It is a  poor artist conception.
I see that it does look like the light path is flowing through the center plain of the mass.
It is following the grid lines below the mass.

Here is a better one. Just clarifying Sorry for the diversion

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« Last Edit: 27/08/2010 02:56:20 by tommya300 »

#### LeeE

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##### Does light curves space and time?
« Reply #6 on: 27/08/2010 19:05:05 »
Does this info have any creditability? Isn't  stanford.edu from Stanford University?

Yes, I believe it is, but it's a bit of a simplification.  An analogy would be to consider the flat ground atop a plateau.  While the ground is flat, the plateau can be of any height - flat ground doesn't have to be at sea-level.

That second diagram is much better

#### yor_on

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##### Does light curves space and time?
« Reply #7 on: 06/09/2010 12:23:38 »
No :)

Light take always the least energy consuming path there is, therefore it also takes the cheapest path. And that makes the light the true master of the straight path. No paths we make can be as straight and to the point as those taken by photons.

Think of it this way, the universe is filled with invincible wrinkles, dips, bends and heights, everywhere gravity sticks up it ugly nose bending SpaceTime, including frame dragging by rotating black holes. And those smart photons just keeps surfing them gravitational 'surfaces'. They exist everywhere, and to my eyes they are the true 'straight lines' in SpaceTime :)

As for a reality check I had better point out that not all photons survive that surfing though, thinking of it again, none does. Ah well, the surf is good while it lasts though.

==
Ah, checking it I see I missed to define by what I meant by 'They exist everywhere', by that I meant the gravitational 'surfaces' existing. They are what the photons ride, well not really, more like travel? Possibly??

==
Hmm, checking that I find myself feeling the need to add that I'm not really sure what travel is for a photon, that's why I found it necessary to write 'Possibly'. You see, a photon can only be observed in its interaction, which also will be its annihilation. We can't observe a photon without destroying it as far as I know.

==
And rereading that I find that I need to add that there might be a new way of 'observing' photons called 'weak measurement' without annihilating them? " Aharonov et al. has proposed weak measurement, in which a measurement apparatus (meter) interacts with the system to be measured so weakly that the state of the system is not significantly disturbed. The readout of the meter from a single run of experiment may be subtle and noisy, but by taking the average over many runs we can correctly estimate the expectation value of the measured observable". For examples of that just Google "Weak measurements and observations physics photons." I believe it to be the rage of the ahem, 'photonic physics community' for the moment :) and it might even work?

==
Just should point out that when you read a physicist mention 'noisy systems' he actually are describing non linear systems, where the paths are undefined, as our universe works at large too. And that when he 'reduces noisiness' he actually most often use so called 'cut offs' to minimize the possible amount of answers. As far as I know linear systems are just a very specialized sub-type to that adapted to, and from, the Newtonian view of our world, the one where 1+1 always would be 2 and where all other answers just was 'noise'.
« Last Edit: 06/09/2010 13:02:20 by yor_on »

#### graham.d

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##### Does light curves space and time?
« Reply #8 on: 06/09/2010 16:11:10 »
It seems to me that if I cause a part of space to have and oscillating electromagnetic field, I am increasing the energy density of that part of space. And this will create a small gravitational field. Please explain why you think this would not be so. You could also think of an object with perfect mirrors either end reflecting light back and forth. The presence of the light would have ben started by adding energy to the device and therefore creating an additional gravitational field. If the mirrors are imperfect the energy will dissipate as heat in the mirrors, but the energy will remain until radiated away.

#### yor_on

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##### Does light curves space and time?
« Reply #9 on: 06/09/2010 22:57:17 »
Graham, you are right there, if it now was me that you replied to?

I think you are right anyway :) If you mean that two light beams moving closely at a parallel same velocity will diverge from their path due to the gravitational influence created by their momentum. What I said no to was "Does light curves space and time?" it curves space infinitesimally while space curves it even more, but it's a timeless, massless boson so it does not curve time, if I by that assume that a photon/light beam in some way would interact with time. But if we assume an unlimitedly strong laser beam, then time as observed by others in its vicinity would perceive a time dilation, when later compared to some far origin. So thinking of it again, maybe you are right, light do 'bend time' but it does not interact with it. Then again, a black hole, or any mass for that sake does just the same don't it, but, do they interact differently than light? Space change around a rotating BH, but so would it around a twirling beam of light, but still, there is a difference somewhere. I had it on the tip of my tongue a moment ago but the bas**d slipped away :) Ahhh got it :)
==

It's about if light is traveling at all. If we assume that it does then I'm bicycling in the blue younder, and if I assume it doesn't? Well, then I'm also bicycling, nes'pa ::))

The idea presented I assume to build on the presumption that light do travel, if it does, we can assume an infinity of light in this universe aka Olbers paradox where the explanation to why the universe ain't the brightest bulb in the sky seems to move around the visible light transforming itself into "microwave wavelengths (1100 times lower than its original wavelength) as a result of the cosmic expansion." I don't know about that but assuming that we had a smaller plasma universe at some time how come it could expand at all, or inflate for that sake?

If I now assume that light doesn't travel, no matter the 'time holding' we see it make, then I don't expect it to bend 'space and time' as it won't exist in those dark waste reaches of our universe. Thanks man, I hadn't thought that one through at all, I knew i had a reason, but it wasn't the one I though as I answered first. Weird :)

Ahh, so many good minds here :)

==
Two differences I think, matter aka invariant mass and rest-mass do age, don't they? So in that motto they do interact with time. Light don't age, ever.
« Last Edit: 06/09/2010 23:07:12 by yor_on »

#### Farsight

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##### Does light curves space and time?
« Reply #10 on: 07/09/2010 14:18:06 »
Energy causes gravity, whether it's matter or light or anything else. Imagine a zillion protons and a zillion antiprotons in a mirrored container. Their presence results in gravity. However they will annihilate, whereupon the mirrored container is full of photons. There is no change to the resultant gravity.

Note that people talk of "curved spacetime" in association with gravity. It isn't curved space or curved time, it's curvilinear motion through space over time.

#### yor_on

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##### Does light curves space and time?
« Reply #11 on: 07/09/2010 16:24:43 »
It's a very weird idea Farsight.
That something not interacting, as light is timeless and massless, will bend space around itself, or if you like make space react to its presence. Matter are a creature of time in that it ages, but light?
===

What confuses me most is what light would do to 'itself', assuming that there at all times are light present in space, and that it do travel. Wish we had a way to see the 'surfaces' created by space wrinkling, as it seems to me that there should be a lot of that, if light travel the same way that matter does.
===

There are of course other aspects that confuses me too, like lights intrinsic timelessness. That fact alone makes it perfectly clear that it do not interact. That we yet can have a definite speed to light seems also a pointer to that light and matter are two different aspects working very differently.

Also from the lights aspect it's hard to see how we could exist, as it have no 'sense of time'. No I'm having real trouble accepting that light travel.
« Last Edit: 07/09/2010 16:42:50 by yor_on »

#### Farsight

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##### Does light curves space and time?
« Reply #12 on: 07/09/2010 17:01:29 »
Light does interact with light, yor_on. See http://discovermagazine.com/2010/jan-feb/083. And have a look at the latest issue of physicsworld where there's an article on displacement current. Then think about an electromagnetic wave. Energy moves from A to B, and as it does there's an electromagnetic field variation, but the photon has no charge, no charged particle is present. Since the field varies, there has to be a current of sorts. But it isn't "conduction current". It's displacement current, and it's alternating. That's why vacuum impedance Z0 = √(μ0/ε0) applies, wherein c = √(1/ε0μ0). Because impedance is resistance to an alternating current. And that displacement really is a displacement. You can't bend something without displacing some part of it it somehow.

As regards gravity, we end up with curved spacetime which is a little different to curved space, but it really doesn't matter whether the energy is configured as light or matter. See The Foundation of the General Theory of Relativity and look at page 185 where Einstein says "the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy". It’s energy that causes gravity, not matter per se. Matter only causes gravity because of the energy content.
« Last Edit: 07/09/2010 17:06:19 by Farsight »

#### yor_on

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##### Does light curves space and time?
« Reply #13 on: 07/09/2010 19:27:18 »
It may be a matter of semantics, but without time, how can one state that light interacts?

Either it is intrinsically timeless, and then it can't interact. And if so, what actions you believe it 'seemingly' to 'choose', will have to be explained from what surrounds it, as I think. Or, it do interact with the 'stuff' around it. But for it to do so it seems to me that you somehow will have to infuse it with a timely structure, invalidating its intrinsic timelessness? So, also invalidating the theory of relativity. Meaning that when we interact we do it in a timely order, involving all. F.e I write this, you cogitate some, then answer, and vice versa naturally :).

So what do we have. On one side light, a structure intrinsically timeless and massless. On the other side matter, having a 'real' invariant mass, interacting with time as it follows its dictates, easily proofed to travel.

And holding both, entropy, aka times arrow.

( You could insert SpaceTime instead there :)
« Last Edit: 07/09/2010 19:28:53 by yor_on »

#### Farsight

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##### Does light curves space and time?
« Reply #14 on: 07/09/2010 23:41:16 »
One doesn't state it, one does the experiemnt, and the experiment proves that light interacts. And it doesn't "invalidate relativity" at all. See http://discovermagazine.com/2010/jan-feb/083

#### yor_on

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##### Does light curves space and time?
« Reply #15 on: 07/09/2010 23:47:59 »
I looked at it, but it's also about how you interpret it Farsight.

#### SuperPrincipia

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##### Does light curves space and time?
« Reply #16 on: 08/09/2010 00:41:38 »
According to General Relativity a geometric theory of gravitation, Mass and Energy curve spacetime in the local vicinity of the mass body. And since mass and energy are convertible both are attractive under the influence of a gravitational field.

The amount or source of spatial curvature (d) caused by the rest mass (m = (E/c²) and energy (E = mc²) is given by the Schwarzschild Radius
(d = (2G/c²)*m)

The amount or source of spatial curvature (d) caused by the photon light energy (E = hf = pc) is given by the Schwarzschild Radius
(d = (2G/c²)*(h/c²)*f)  = (2G/c³)*p)

Conclusion, Rest mass and energy provides more curvature to the spacetime than the photon electromagnetic energy.

www.SuperPrincipia.com [nofollow]

« Last Edit: 08/09/2010 00:55:07 by SuperPrincipia »

#### yor_on

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##### Does light curves space and time?
« Reply #17 on: 08/09/2010 01:42:46 »
Don't think anyone will argue against that SP :)

If it was anywhere near to be light having the stronger gravitational effect we would see some truly strange effects every time we observed a beam.

#### LeeE

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##### Does light curves space and time?
« Reply #18 on: 08/09/2010 21:33:00 »
According to General Relativity a geometric theory of gravitation, Mass and Energy curve spacetime in the local vicinity of the mass body. And since mass and energy are convertible both are attractive under the influence of a gravitational field.

Whoa!! - hang on there a couple of seconds...

Let's avoid any sloppy thinking here: by saying that energy and mass are inter-convertible we are also very clearly saying that they are not the same, for if they were the same then there would be no scope for conversion between one and the other.

#### SuperPrincipia

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##### Does light curves space and time?
« Reply #19 on: 08/09/2010 22:16:17 »
To say that matter (mass) and energy are convertible means that very small amounts of mass can be converted into large amounts of energy and vice versa; according to Einstein's (E = mc²)!

But don't take my words for it, take it from Einstein himself:

www.SuperPrincipia.com [nofollow]

« Last Edit: 08/09/2010 22:27:52 by SuperPrincipia »

#### Farsight

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##### Does light curves space and time?
« Reply #20 on: 09/09/2010 15:05:53 »
SuperPrincipia: please can you run through that conclusion again. You're saying

(d = (2G/c²)*m)

and

(d = (2G/c³)*p)

wherein E=hf and p=hf/c, but a 511keV electron and 511keV positron can undergo annihilation to two 511keV photons. Looking at just the electron for simplicity, we started with E=mc² = 511keV and finished with E=hf = 511keV. Did you mean to say spatial curvature (d) rather than spacetime curvature?

All: regardless of the above, the energy content of light does have a gravitational effect, as does the energy content of matter. It's just that you need an enormous body like the sun to see even a small deflection, so there's very little in a light beam. Somewhat separate to this, light does interact with light, we can see it in a lab. There's a difference between curved space and curved spacetime. In a room, the spacetime is said to be curved, and a thrown ball follows an arc. But if you throw the ball faster, the arc is flatter. If the space in the room was curved, the ball would follow the same arc no matter how fast you threw it.

#### SuperPrincipia

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##### Does light curves space and time?
« Reply #21 on: 09/09/2010 16:43:04 »
Farsight it appears that you have grasped the equations!

Rest Mass
(d = (2G/c²)*m)

and Electromagnetic Photon Mass-Energy

(d = (2G/c³)*p)

I my opinion the above equations predict how matter and energy create the maximum amount of curvature in the minimum amount of space; as we measure length, area, and volume.

Differences between space and spacetime are somewhat trivial but not too difficult to handle. What I interpret you stating is that if and inertial rest mass is made to traverse an orbit in a gravitational field at non relativistic speeds (speeds much less than the speed of light) matter curves space in a way that it follows a typical Newtonian Arc.

If that same inerial mass is made to traverse an orbit in a gravitational field at relativistic speeds (speeds close to the speed of light) the mass gets heavier and curves space just a little more; and in a way that it follows an Einstein Arc.

Where you are claiming that the larger mass creates more spacetime curvature (m′ = m/sqrt(1 - (v/c)²))

And I have to be honest with you, I am not sure that the spatial of spactime gets smaller with increasing mass; the space of spacetime will probable increase in a gravitational field in the local vicinity of a free mass body moving at relativistic speeds in a gravitational field.

For me the term space is used when dealing with static geometry. Anytime we are talking about orbits, mass in relativistic motion, or when discussing mass relative to the vacuum of spacetime; we can use the term spacetime. Anytime we are discussing Schwarzschild Radius curvature we are talking about spacetime; or how mass, space, and time interact with the vacuum of the cosmos.

www.SuperPrincipia.com [nofollow]

#### Farsight

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##### Does light curves space and time?
« Reply #22 on: 09/09/2010 22:39:47 »
Thanks Superprincipia. Best if I spell out the way I see it in simple terms: the electromagnetic field is curved space, and the gravitational field is curved spacetime. But let's not dwell on it, let's just concur that it's a concentration of energy that causes gravity, whether it's configured as mass or light or anything else.

So does light curve space and time? The answer is: yes, it does.

#### Geezer

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##### Does light curves space and time?
« Reply #23 on: 10/09/2010 06:26:38 »
Light does interact with light, yor_on. See http://discovermagazine.com/2010/jan-feb/083.

What they say in the abstract is:

"Here, we experimentally demonstrate a bipolar optical force between planarly coupled nanophotonic waveguides."

I think it might be a bit of a stretch to infer that this is proof that light interacts with light.

#### JP

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##### Does light curves space and time?
« Reply #24 on: 10/09/2010 06:35:03 »
You're right.  It's a light-matter interaction, Geezer.   It also doesn't have anything to do with general relativity.

#### The Naked Scientists Forum

##### Does light curves space and time?
« Reply #24 on: 10/09/2010 06:35:03 »