# Can you make a battery out of light slowing materials?

#### arusse02

I've read about light slowing materials, and i'm wondering if you could slow down light enough, could it be used to say store light from the sun during the day so solar panels could work at night? Or would it not work because the process of slowing light down gradually absorbs some of the light/too much energy would be lost over a 12 hour period? Does it seem plausible to store sunlight this way?

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#### davenn

Gold Member

it doesn't slow materials

It slows IN materials ( aka different mediums

Does it seem plausible to store sunlight this way?
not with any known technology that I am aware of

#### scottdave

Homework Helper
Well if you could build a lossless material, I don't know that you'd gain that much. Take a look at the table of indexes for some materials. https://en.wikipedia.org/wiki/List_of_refractive_indices

It looks like the highest one is Germanium, where light travels 4 times slower. So if light normally takes 8 minutes to get here from the Sun... If you could build a 93 million mile column of germanium, then that light will take 32 minutes to reach us. Not much gain there. I guess someone could coil some fiber optic, but how much is that going to cost, compared to the gain?

How about put some satellites up to collect the energy and beam it down to us? Something like this- https://www.energy.gov/articles/space-based-solar-power

#### arusse02

Well if you could build a lossless material, I don't know that you'd gain that much. Take a look at the table of indexes for some materials. https://en.wikipedia.org/wiki/List_of_refractive_indices

It looks like the highest one is Germanium, where light travels 4 times slower. So if light normally takes 8 minutes to get here from the Sun... If you could build a 93 million mile column of germanium, then that light will take 32 minutes to reach us. Not much gain there. I guess someone could coil some fiber optic, but how much is that going to cost, compared to the gain?

How about put some satellites up to collect the energy and beam it down to us? Something like this- https://www.energy.gov/articles/space-based-solar-power
Wikipedia has much more efficient examples:

"
In 1998, Danish physicist Lene Vestergaard Hau led a combined team from Harvard University and the Rowland Institute for Science which succeeded in slowing a beam of light to about 17 meters per second,[1] and researchers at UC Berkeley slowed the speed of light traveling through a semiconductor to 9.7 kilometers per second in 2004. Hau and her colleagues later succeeded in stopping light completely, and developed methods by which it can be stopped and later restarted.[2][3] This was in an effort to develop computers that will use only a fraction of the energy of today's machines.[4]

In 2005, IBM created a microchip that can slow down light, fashioned out of fairly standard materials, potentially paving the way toward commercial adoption.[5]"

https://en.wikipedia.org/wiki/Slow_light

So it looks like its been slowed significantly more than only 4 times. Not sure of the losses here or the power or technique required to slow light, but it seems like if they got to 17 m/s, then can probably do much better.

#### arusse02

it doesn't slow materials

It slows IN materials ( aka different mediums

not with any known technology that I am aware of
light slowing materials means the same thing as a material that slows light.

Are the examples I included from wikipedia in the post above usable?

#### davenn

Gold Member
light slowing materials means the same thing as a material that slows light.

yeah, I guess you could interpret it that way

#### Baluncore

Are the examples I included from wikipedia in the post above usable?
It depends on what light is considered to be, and what is meant by slowing it down.
How many photons are being slowed down, or stored at the time?
It takes many photons to generate significant energy.
One watt needs about 1019 photons of light per second.
How can you store all those individual photons, then release them later as you need them?

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#### DaveC426913

Gold Member
Does it seem plausible to store sunlight this way?
Well, it would be more efficient to take the photon energy and convert it - for the purpose of storage - to a form that doesn't start off moving at the speed of light. You wouldn't have to downshift the speed. This happens pretty seamlessly with electrons. You could store them in some sort of battery.

#### hmmm27

Doesn't anybody remember the SF story Light Of Other Days ?

Well, it would be more efficient to take the photon energy and convert it - for the purpose of storage - to a form that doesn't start off moving at the speed of light. You wouldn't have to downshift the speed. This happens pretty seamlessly with electrons. You could store them in some sort of battery.
And, if the pane of "glass" in front of the PV cell allowed some light through quickly, and slowed the rest down for 12 hours or so, you'd need fewer batteries. Fine tune it with different speeds and you could match throughput to anticipated electricity demand and not need a battery at all.

Still, it would probably be easiest to imagine for a skylight or home-heating system. Or, a flashlight that if you left it out for a few days, could be used to incinerate things.

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#### Nik_2213

Funnily enough, I remember 'slow glass' from one of the prequel tales, where cars fitted with a 'new, improved' type of laminated safety glass suffer a spate of weird, apparently inexplicable collisions. The few survivors all claim, 'But I looked and the road was clear'.

The common factor was the 'look angle', diagonally rather than directly through the glass. That gave just enough delay to be dangerous...

The effect tamed, spin-offs included panels with staggered delays for street-lighting, mirrors that let you see your back when you turn etc etc...
--
IIRC, the incinerator torch was a Larry Niven, 'Gil the ARM' tale, involving a 'time accelerator' device and drug-dealers peddling insulin...

#### DaveC426913

Gold Member
Funnily enough, I remember 'slow glass' from one of the prequel tales, where cars fitted with a 'new, improved' type of laminated safety glass suffer a spate of weird, apparently inexplicable collisions. The few survivors all claim, 'But I looked and the road was clear'.

The common factor was the 'look angle', diagonally rather than directly through the glass. That gave just enough delay to be dangerous...
I challenge this.
Glass does not slow light sufficiently to result in car accidents.

I'll posit that what they mean is the glass refracts the view, so that objects near the periphery are not visible when they should be. Their appearance in a driver's peripheral vision will be effectively delayed a few fractions of a second because of the refractive distortion.

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#### Nik_2213

{Cough}
This was SciFi, with 'one impossible thing', cunningly crafted from 100% 'Handwavium'.
In the cycle of 'Slow Light' tales, it did...

( IIRC, in the prequels, crash investigators did check those windscreens for a possible 'blind spot' due refractive index, found nothing amiss. I can't remember the precise circumstances that revealed the 'impossible' cause... )

FWIW, for very good reason, many, many real cars' subtly curved wing-mirrors are discreetly labelled, 'Objects seen in mirror are closer than they appear'. Sadly, takes but scant misjudgement to spawn disaster...

#### DaveC426913

Gold Member
I remember 'slow glass' from one of the prequel tales,
The fact that this was from a sci-fi book went right over my head.

#### hmmm27

The only one I knew existed, from Shaw's Slow Glass set, was whichever one was a murder mystery (?) which I read probably well over 40 years ago. The Niven reference also, though I now remember the story (a "locked room" mystery, IIRC).

The fact that this was from a sci-fi book went right over my head.
And, that's what you get for cycling around in winter without accounting for windchill : brain freeze

Meanwhile back at the ranch (and let's not worry about who got the conversation wandering off ), the OP's Wikipedia link on Slow Light leads to another article on research where they not only slowed light down but converted it into a matter stream.

Light stopped then converted to matter - Photonics.com 2007

Done at a couple billionths of a degree above absolute zero, so not coming to a picture window near you, anytime soon.

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"Can you make a battery out of light slowing materials?"

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