<story><title>Does light have an infinite lifetime?</title><url>https://bigthink.com/starts-with-a-bang/light-infinite-lifetime/</url></story><parent_chain><item><author>dataflow</author><text>Something about this doesn&amp;#x27;t make sense. This means that, from its own perspective, every photon is emitted at time T at location x, then absorbed at time T at location y, meaning there is no time &amp;quot;in between&amp;quot; those... yet somehow, at a &lt;i&gt;distinct&lt;/i&gt; point in between those events, an object can get in the way and block the photon from reaching point y. Meaning you have two points in time that have the same value but aren&amp;#x27;t identical? How does that work, mathematically? Do you need nonstandard calculus or something to make sense of it?</text></item><item><author>henry2023</author><text>From the perspective of a photon, there is no such thing as time. It&amp;#x27;s emitted, and might exist for hundreds of trillions of years, but for the photon, there&amp;#x27;s zero time elapsed between when it&amp;#x27;s emitted and when it&amp;#x27;s absorbed again. It doesn&amp;#x27;t experience distance either.</text></item></parent_chain><comment><author>fnordpiglet</author><text>This is because a photon has no mass and always travels at the speed of light in all reference frames. A photon never observes time because the effects of time dilation at the speed of light is infinite and due to relativity they don’t experience the events between their emission and absorption as they don’t decelerate when they’re absorbed. In a very real sense from the photons perspective they never exist and don’t experience a temporal dimension. However from a frame of reference less than the speed of light - which all objects of mass experience - we can observe their creation, propagation, and absorption.&lt;p&gt;Reality is stranger than fiction!!</text></comment>
<story><title>Does light have an infinite lifetime?</title><url>https://bigthink.com/starts-with-a-bang/light-infinite-lifetime/</url></story><parent_chain><item><author>dataflow</author><text>Something about this doesn&amp;#x27;t make sense. This means that, from its own perspective, every photon is emitted at time T at location x, then absorbed at time T at location y, meaning there is no time &amp;quot;in between&amp;quot; those... yet somehow, at a &lt;i&gt;distinct&lt;/i&gt; point in between those events, an object can get in the way and block the photon from reaching point y. Meaning you have two points in time that have the same value but aren&amp;#x27;t identical? How does that work, mathematically? Do you need nonstandard calculus or something to make sense of it?</text></item><item><author>henry2023</author><text>From the perspective of a photon, there is no such thing as time. It&amp;#x27;s emitted, and might exist for hundreds of trillions of years, but for the photon, there&amp;#x27;s zero time elapsed between when it&amp;#x27;s emitted and when it&amp;#x27;s absorbed again. It doesn&amp;#x27;t experience distance either.</text></item></parent_chain><comment><author>cmsj</author><text>I am not a Physicist, so please don&amp;#x27;t rely on this, but my understanding is that this comes down to the frames of reference in special relativity.&lt;p&gt;If you&amp;#x27;re in a car on the highway, an observer standing still outside the car sees you moving at 50mph, but an observer inside the car with you, sees you not moving at all, but the world rushing past at 50mph. These are two different reference frames, and the second one is called a rest frame - any object can be considered to have a rest frame of reference where it isn&amp;#x27;t moving at all. Any object that is, which has mass.&lt;p&gt;Massless objects are always observed to be moving at the speed of light by any observer in any frame of reference. This is one of the most mind-bending parts of relativity, but it ultimately connects to the part of special relativity where speed affects time - the faster you go, the slower your clock runs compared to things moving slower than you, and the closer you get to the speed of light, the closer your clock gets to zero. Massless particles only travel at the speed of light, and thus have no clock, therefore they experience no time.&lt;p&gt;I hope I got that right, but even if I did, I still don&amp;#x27;t feel like I actually understand it at all!</text></comment>