UCSB Science Line
 Would light ever stop traveling if there were no objects to absorb the light. Question Date: 2011-10-13 Answer 1:The simple answer to your question is that light will keep going until it interacts with something. It's really quite remarkable! Where could we test this? We see exactly this in deep space! In fact, scientists have observed light that has been travelling for over 13 billion years. 13 000 000 000. To get an idea of how big the number is, that's like comparing one second to 300 years. Or comparing the width of a human hair (1 mm divided by 10), to the distance between here and the Oregon border (620 miles). For more examples, it's like comparing the size of an ant (~5mm, or 1/5 of a inch) to the length of the Earth's equator (40 075 km, or 24 900 miles), or 3 cm (~1 inch) to the distance to the moon! (384 000 km, 239 000 miles). As you can see, light travels for a very long time if nothing gets in its way. We know from experiments that energy is always conserved, so unless there's something to which light can transfer its energy--and there's not much in deep space--it will keep going! Reference: NASA, science-nasa Answer 2:No, in fact light only stops when it is absorbed by an electron in an atom of an object. Light in a perfect vacuum travels on at its full speed until it hits something. That is why it is so cool that when we see really ancient images of far off "and very, very old" objects, that light has traveled from that star through the universe for sometimes billions of years and the first object it hit was our telescope detector. Answer 3:If there were no objects to absorb light, it would keep traveling forever. Light is made up of particles called photons that travel like waves. Unless they interact with other particles (objects), there is nothing to stop them. Unlike some types of particles, they do not decay, meaning that they do not spontaneously turn into other types of particles. With nothing to stop them and no chance of decaying, the will keep going forever. However, scientists do not know what shape the universe is or what would happen when the photon reaches the"edge" of the universe, if the universe even has an edge. Physicistsare still doing research to be able to answer questions like this. For instance, physicists want to know whether or not the universe is infinite, meaning that it goes on forever. If it is infinite, the light would travel forever. If it is compact (the mathematical term for "non-infinite space"), then it is still possible for the photons to travel forever because depending on the topology (the mathematical term for "shape and symmetry") of the universe, it may be possible for the photons to wrap around to the "other side" of the universe and keep going. Answer 4:Ordinarily, no, light will continue on its path forever unless it runs into something. Now, this said, very powerful photons (i.e. gamma rays) can spontaneously transform into particle-antiparticle pairs. I don't know if there are any conditions necessary for this to happen, though. Note from a scientist: "There are requirements for this. The gamma ray must be in the vicinity of a massive object, for example a nucleus, for the particle - antiparticle pairs to really exist. This is known as 'pair production'. If this happens when there is no external mass present, then the pair must have the same momentum and therefore will mutually annihilate instantly, creating a photon of the same original energy and momentum. This is a contributor to the vacuum energy, and these 'virtual particles' are produced all the time in a vacuum but have no real net effect in normal physics, although it does lead to some interesting implications such as the Casimir effect and Hawking radiation." Answer 5:We have no reason to believe that light would ever stop traveling if there were no objects in its path to scatter or absorb it. We detect light from sources light years away with our telescopes all of the time. Hope this helps Answer 6: Nope! Light is a self-perpetuating electromagnetic wave; the strength of the wave can get weaker with the distance it travels, but as long as nothing absorbs it, it will keep on propagating forever.Click Here to return to the search form.

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