Using frozen light as a starship shield

Question

Frozen/Solid light Shields

I can't find much online; but after listening to an Isaac Arthur episode where he briefly mentions frozen light, I immediately thought about the Hardlight items from the Halo series.

My basic idea: being able to control the light and the distance it can travel so that it becomes frozen in place a certain distance from the emitter. So a ship would have hundreds or thousands of these shield projectors to create overlapping coverage of the ship.

Now I am thinking, since this might require lots of energy, that the shields will be an active defence and only turn on when a sensor picks up an incoming attack. From a scientific point of view, would these shields be able to stop any physical matter, of would they only be useful against laser attacks? (If even useful against those at all).

The shields would experience fatigue then and need to cool down after prolonged use. This would give the Star Trek effect of "forward shields at 40%". Except instead of diverting power to the shields to increase their duration it would be diverting cooling to the shields since the ships will have limited cooling abilities.

Does this seem feasible or am I way off the ball on this? I guess is this technology into feasible as information and communication devices or can it have physical applications.

Essentially, I want to neutralize laser weapons on warships and have a space navy that relies on physical kinetic and explosive weapons.

Answer 1

Light can be trapped, slowed or reflected in a medium, but not frozen in a vacuum except by gravity

Light is essentially an oscillation in the Electro-Magnetic field. The wave nature of the light propagates through space (a vacuum) at speed. The smallest quantity of light is called a photon - these are massless and move at 'the speed of light', or more accurately, the 'speed of causality'.

Light can be slowed to a standstill in a medium, as in this article. Even simple water will slow light - being caused by interference with electrons. Trapping the light in a crystal is possible, at least for a moment, by having light constantly interacting with electrons in the crystal in precise conditions. These precise conditions however are easy to deteriorate, so the light eventually will start moving again.

The only way I could think of to 'freeze' light in a vacuum is to bend space, through General Relativity. Currently the only way to achieve this is to use a black hole, where light emitted by an object at the event horizon will remain stationary.

For your shield, perhaps space could be warped, or gravitons discovered (we haven't discovered this yet) that allow you to 'freeze' light in space, if we can manipulate it. You have inadvertently discovered the gap we have in our knowledge at the moment, between that of General Relativity and Quantum Field Theory.

BTW: Keep in mind that light travels at the speed of causality - so the light beam experiences no 'time'. So you could accurately say that every light beam is indeed 'frozen' from the point of view of its own frame of reference. This revelation was what made Einstein conceive of the Theory of Special Relativity.

Answer 2

As 'light' refers usually to 'for humans visible light' I will focus my answer at this. And my answer is: that will get difficult.

Visible light, defined as photons and waves, has nearly no impact on physical matter, as described on Wikipedia like this:

Light exerts physical pressure on objects in its path, a phenomenon which can be deduced by Maxwell's equations, but can be more easily explained by the particle nature of light: photons strike and transfer their momentum. Light pressure is equal to the power of the light beam divided by c, the speed of light. Due to the magnitude of c, the effect of light pressure is negligible for everyday objects. For example, a one-milliwatt laser pointer exerts a force of about 3.3 piconewtons on the object being illuminated; thus, one could lift a U.S. penny with laser pointers, but doing so would require about 30 billion 1-mW laser pointers.

There is the idea to use light pressure for engines of spaceships in form of solar sails, but the energy-source for this pressure is a whole sun, you will not reach this energy level with engines that easy (if you do, you would at least have a starting point for your technology).

As light does not block itself you will not be able to use light against a laser I think.

Answer 3

@flox gave an excellent answer; explaining the quantum nature of light (technically described by a massless boson which is the carrier for the electromagnetic force). For further discussion of the non-local nature of light in the absence of an electromagnetic potential see my answer and comments here.

Quantum electrodynamics, the field which describes the electromagnetic interaction from a quantum (non-classical) viewpoint, is so accurate that it has been called "jewel of physics". This is to say that the way that light and the electromagnetic force interact is very well understood and the theory does not allow for electromagnetic radiation itself to produce bound, localized states in the absence of media (mass-carrying particles). @AlexP has a comment which highlights the difference in terminology and theory very well, while the electromagnetic interaction hasn't changed, there are new discoveries regarding the phenomena the interaction produces; semantics and journalistic sensationalism playing a large role here.

From a scientific point of view, would these shields be able to stop any physical matter, of would they only be useful against laser attacks?

Even in Halo, the "energy shields" are described as an electromagnetic field effect, since the field shown contain closed loops, it is not consistent with free-space electromagnetic waves. Thus from a fundamental scientific point of view, you would need the electromagnetic waves to be confined to a medium to produce the desired effects, what the medium is and the phenomena produced by the interaction however, is up to you and can always be described with hand-wavy physics without breaking fundamental laws.

Answer 4

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It might work very well as a Whipple Shield.

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Assumptions: We will assume that some new physics is discovered that allows light to be frozen in place with a relative velocity of zero, in complete violation of known laws. This "wall of light" would be invisible (you can't see light until it hits you in the eye), unless you introduced the extra rule that this "stationary light" is not entirely stable and decays into ordinary propegating light waves over time: in this case your shield will glow exactly as we might want to make it look awesome.

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When the projectile (lets say a missile or a bullet) hits your wall of light the light will not stop it at all, light exerts next to no pressue on objects. However, some of the light will be absorbed, so it will heat up the missile/projectile.

Heating up an inbound projectile is actually a very standard way of protecting against tiny meteors (bullet sized) in space. When the projectile heats up it will evaporate into a ball of gas. Being hit by a beach-ball sized blob of warm gas is like being burped at, it is much, much less dangerous that being hit by a hard little rock or a bullet. Traditionally their is a thing called a "Whipple Shield" : a thin layer of metal (maybe a bit thicker than tinfoil) that makes the bullet/meteor evaporate into gas, then you have a gap to give this gas blob time to spread out. https://en.wikipedia.org/wiki/Whipple_shield

So your shield could be used the same way. You light-wall might have some advantages compared to the metal ones. It might be less heavy (although you would need some kind of generator to power yours), it might be adaptive: so you can change the distance you project the light-wall ahead of you in response to the speed/composition and size of the enemy's projectiles.

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Whether or not the thing works against laser weapons is entirely up to you as a world-builder and known physics has no prejudice against either choice. You could say it does work, because whatever thing you have that holds light in place stops the new light, or you could say it doesn't because it doesn't.

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Suggestion for the "physics". Just don't say anything. The entire thing is outside known physics, which is completely fine. Its the future. If someone told people in the 18th Century about the power of nuclear weapons they would complain that no chemical could possibly be that explosive. The same could happen again.