Photon Momentum: The Impact of Light on Movement in Space

Click For Summary

Discussion Overview

The discussion revolves around the concept of photon momentum and its effects on movement in space, particularly in scenarios involving a flashlight and the impact of starlight. It explores theoretical implications and applications, such as solar sails and the Pioneer anomaly.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants assert that turning on a flashlight in space would push the individual in the opposite direction, referencing Newton's third law.
  • Others mention that the momentum of photons is indeed a principle behind solar sails and relate it to the Pioneer anomaly.
  • One participant emphasizes that momentum is conserved and reiterates the initial questions regarding the effects of photons on movement.
  • Another participant provides a calculation for photon momentum, stating that the momentum change upon reflection would result in forward movement, assuming normal incidence.
  • There are references to current initiatives exploring the use of laser propulsion for light sails targeting exoplanets.

Areas of Agreement / Disagreement

Participants generally agree on the concept that photons possess momentum and can exert forces, but there are varying interpretations of the implications and applications of this momentum, indicating that multiple competing views remain.

Contextual Notes

Some assumptions about the conditions in space and the nature of photon interactions are not fully explored, and the discussion does not resolve the complexities of momentum transfer in different scenarios.

Who May Find This Useful

Individuals interested in the physics of light, momentum, space exploration technologies, and theoretical applications of photon momentum may find this discussion relevant.

Ebi
Messages
13
Reaction score
3
TL;DR
Can momentum of photons create impact forces?
We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if:
1- I turn on a flashlight (torch), would I be pushed in the opposite direction which the flashlight is facing (Newton's third law)?
2- If a star is shedding light on me (its photons hit my body), would I start moving due the impact of photos?
 
Physics news on Phys.org
Yes. That's the principle behind solar sails. Also what was deemed to be the cause of the Pioneer anomaly.
 
  • Like
Likes   Reactions: Klystron, vanhees71 and Ebi
Ebi said:
Summary:: Can momentum of photons create impact forces?

We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if:
1- I turn on a flashlight (torch), would I be pushed in the opposite direction which the flashlight is facing (Newton's third law)?
2- If a star is shedding light on me (its photons hit my body), would I start moving due the impact of photos?
Yes, momentum is momentum and it's conserved!
 
  • Like
Likes   Reactions: Vanadium 50 and vanhees71
Yes, the momentum of a photon is given by h/lambda. And when the photon hits you and reflects back, the change in the momentum of photon is given by 2h/lambda (assuming normal incidence), you would start moving forward with that momentum.
The momentum of photons (from sunlight) have been used in the past to propel spacecraft s and are called as solar sails. There are efforts currently by breakthrough initiatives, to use ground based laser source to propel light sails to the exoplanet Alpha Centauri. Follow this link to learn more about that.
 

Similar threads

  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
Replies
3
Views
2K
  • · Replies 8 ·
Replies
8
Views
1K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 2 ·
Replies
2
Views
1K