Storing light and using it to propel an object

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In summary: ...be constantly on, or else the rocket will eventually run out of photons.true...be constantly on, or else the rocket will eventually run out of photons.true
  • #1
J3J33J333
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TL;DR Summary
Using Light as spaceship fuel
Is it possible to store large quantities of light for extended periods of time? If so would it make any sense to use it to propel a spaceship because it doesn't weigh anything? I read that one of the biggest issues with getting to space is the weight of the fuel.
 
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J3J33J333 said:
Summary: Using Light as spaceship fuel

Is it possible to store large quantities of light for extended periods of time?
no
J3J33J333 said:
If so would it make any sense to use it to propel a spaceship because it doesn't weigh anything?
no
J3J33J333 said:
I read that one of the biggest issues with getting to space is the weight of the fuel.
true
 
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  • #3
J3J33J333 said:
Summary: Using Light as spaceship fuel

Is it possible to store large quantities of light for extended periods of time? If so would it make any sense to use it to propel a spaceship because it doesn't weigh anything? I read that one of the biggest issues with getting to space is the weight of the fuel.
Theoretically, one of the most efficient means of accelerating in emty space is a photon rocket:

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

Note that a container full of light would in fact have a mass related to its total energy content.
 
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PeroK said:
Theoretically, one of the most efficient means of accelerating in emty space is a photon rocket:
OK, guess I was wrong about it being a good means of propulsion. Directly "storing light" still makes no sense. Have a light GENERATOR, as you pointed out, is a different thing and not what I interpreted the OP as meaning.
 
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  • #5
phinds said:
OK, guess I was wrong about it being a good means of propulsion. Directly "storing light" still makes no sense. Have a light GENERATOR, as you pointed out, is a different thing and hot what I interpreted the OP as meaning.
You're right, I was basically wondering if anyone knew about materials that have seriously low photon attenuation with good internal reflection. The photon rocket does help a good chunk with what I'm trying to figure out
 
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PeroK said:
Theoretically, one of the most efficient means of accelerating in emty space is a photon rocket:

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

Note that a container full of light would in fact have a mass related to its total energy content.
What can i look up to calculate the mass?
 
  • #7
J3J33J333 said:
What can i look up to calculate the mass?
The mass, ##M##, of a box of light in the centre of momentum frame of the box is given by:
$$Mc^2 = E$$ where ##E## is the total energy of all the photons in the box.

Note that if you have only one photon, then there is no centre of momentum reference frame. And this invariant mass, ##M##, cannot be defined.
 
  • #8
J3J33J333 said:
I was basically wondering if anyone knew about materials that have seriously low photon attenuation with good internal reflection.
You might be interested in the work of Kerry Vahala, a former classmate and one of the smartest people I ever met. He can build small optical resonators with Q → 1011, similar to "whispering galleries" IIRC. They're not for bulk energy storage so much as metrology.

BTW, the materials are basically glass and such. Also, it doesn't take too long for light to bounce around a resonator 1011 times.
 
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  • #9
You can use the rocket equation to figure out the (theoretical) delta-V possible with pure photon exhaust by setting exhaust speed ##v_e## equal to ##c##, the speed of light in vacuum. A PeroK mentions, you can relate the corresponding propellant mass (e.g. the trapped photons or corresponding matter/anti-matter) with the energy "required" to fuel up the rocket for a particular mass ratio using ##E = mc^2##.

For instance, if you would like to know how much "photon energy" ##E_p## is needed for a particular ##\Delta v## for a spaceship with mass ##m_f## after the "burn", then the relationship can be derived to be ##E_p = m_f c^2 (e^{\Delta V / c} -1 )##. Propelling something to, say, 1% of ##c## would thus take around 900 TJ per kg of spaceship. Note that for high delta-V's you need to consider a relativistic rocket to find the actual "physical" speed after such a burn.
 
  • #10
phinds said:
no
He's totally right and that "no" makes storing light in a bucket, to use later, a real non-starter, even with a very shiny bucket.

There's an arm waving objection to the whole notion and that is that light is an essentially kinetic form of energy which is being dissipated or absorbed all the time. Using mechanical kinetic energy for transport is pretty uncommon (apart from freewheeling down hill on your bike and your momentum taking you to nearly the top of the next hill). The Gyrobus was one of those rare examples.

Using a photon beam, on the other hand, is one of many contenders for long distance travel with high final speeds, after many years of the drive being switched on. But the photon beam has to be generated at the time it's used.
 
  • #11
sophiecentaur said:
even with a very shiny bucket
:oldlaugh:
 

Related to Storing light and using it to propel an object

1. How is light stored?

Light can be stored using a process called electromagnetically induced transparency, which involves trapping light inside a medium such as a gas or crystal. Another method is to use mirrors or other reflective surfaces to bounce light back and forth, effectively storing it.

2. Can light be used to propel an object?

Yes, light can be used to propel an object through a process called radiation pressure. When light is absorbed or reflected by an object, it exerts a force on that object, causing it to move in the direction of the light.

3. What types of objects can be propelled by light?

Objects of any size and material can be propelled by light, but the amount of force exerted will vary depending on the object's size, shape, and reflective properties. Small, lightweight objects such as spacecrafts or nanoparticles are commonly propelled by light.

4. Is storing light and using it to propel an object energy efficient?

Yes, storing light and using it to propel an object can be very energy efficient. Since light travels at the speed of light, it can cover large distances in a short amount of time, making it a very efficient means of propulsion. Additionally, using light eliminates the need for traditional fuels, making it a more sustainable option.

5. What are the potential applications of storing light and using it to propel an object?

The potential applications of this technology are vast and include space exploration, propulsion of spacecrafts, solar sails, and even transportation on Earth. It could also have applications in medical technology, such as propelling tiny medical devices within the body, and in nanotechnology for precise manipulation of small objects.

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