# Does a photon observe other photons moving past it at the speed of light?

*They say that the speed of light is the same for all inertial observers, but what if the observer is a particular photon within a laser beam? Each photon in a laser beam would see all the other photons passing it at speed c, therefore the laser beam would instantly break up. How do you solve this conundrum?*

The answer is that a photon can't count as an observer. Time slows down for objects that move at close to the speed of light. For an object moving *at* the speed of light, time would grind to a halt. So how fast you clock something moving past you if you can't measure time turns out to be a nonsensical question.

# Still Curious?

**Get More 'Curious?' with Our New PODCAST:**

- Podcast? Subscribe? Tell me about the Ask an Astronomer Podcast
- Subscribe to our Podcast | Listen to our current Episode
- Cool! But I can't now. Send me a quick reminder now for later.

**Related questions:**

- Why can't relative velocities add up to more than the speed of light?
- Why doesn't light from distant galaxies reach us instantaneously?

**More questions about The Theory of Relativity:** Previous | Next

# How to ask a question:

If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.

Main Page | About Us | For Teachers | Astronomy Links | Ask a Question | View a Random Question | Our Podcast

Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't existURL: http://curious.astro.cornell.edu/question.php?number=574

This page has been accessed *20978* times since September 16, 2003.

Last modified: *September 16, 2003 11:28:20 PM*

Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.

**Warning: Your browser is misbehaving! This page
might look ugly.** (Details)