How far the light can be shine?

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Discussion Overview

The discussion revolves around the distance that light can travel, exploring concepts related to light speed, astronomical observations, and methods used to determine the age of light from distant objects. The scope includes theoretical considerations, observational astronomy, and the implications of light's interaction with various environments.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that light travels at approximately 300,000 km/s and question how far it can actually reach.
  • One participant mentions that we can see stars, implying that light from them has traveled vast distances.
  • Another participant states that light can continue traveling until it interacts with something, suggesting that its journey is not limited by distance alone.
  • Several contributions reference the observation of objects up to 13 billion light years away, discussing the implications of such distances.
  • Questions arise about how scientists determine the age of the light received from distant objects, with references to indirect methods such as redshift and standard candles.
  • Some participants express skepticism about the precision of methods used to measure distances and ages of light, particularly regarding parallax and other techniques.
  • There is a discussion about the role of inertia in electromagnetic radiation, with differing views on its applicability to light.
  • Participants mention various methods used for measuring distances to stars and galaxies, including redshift and type 1a supernovae, while noting that these methods vary in accuracy depending on the distance of the objects.
  • One participant humorously suggests that catching light with the eye might be preferable to using a CCD for extremely distant photons.

Areas of Agreement / Disagreement

Participants express a range of views on the methods used to measure the distance and age of light, with some agreeing on the general principles while others challenge the precision and applicability of those methods. The discussion remains unresolved regarding the effectiveness of various techniques and the implications of light's interaction with its environment.

Contextual Notes

Limitations include the dependence on definitions of distance and age, the accuracy of measurement methods, and the unresolved nature of how light interacts with different environments.

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light can be speed faster about 300,000 km/s,
but how long the distance that light can be arrive?
 
Science news on Phys.org
You can see stars, can't you?
 
Any distance until it interacts with something.
 
We've observed objects as distant as about 13 billion light years. So, we know of light that has traveled that far. (For reference, 13 billion light years is a little more than 1.2*10^26 meters. That's 120 trillion trillion meters, which is about 75 billion trillion miles.)
 
Parlyne said:
We've observed objects as distant as about 13 billion light years. So, we know of light that has traveled that far. (For reference, 13 billion light years is a little more than 1.2*10^26 meters. That's 120 trillion trillion meters, which is about 75 billion trillion miles.)

How do the scientists conclude that the particular light we received is x years old?
 
light year rings...

i would imagine triangulation and knowing the speed of light would be an unrealistically simple way of doing it...
 
Inertia still applies for EM radition, so i believe it depends entirely upon the environment into which you are shining the radiation. Since the majority of space is nearly a perfect vacuum EM radiation will countinue along its original vector until acted upon by an outside force ie... black hole, nebula, telescope ect. Someone please correct me if I am wrong.
 
dst said:
http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/970415c.html


Doesn't sound all that precise to me, parallax aside?
Most of those methods are highly accurate, especially since stars tend to fit a very tight band of types.

Note, though, that those methods are used for stars in our galaxy. For more distant stars/galaxies, they use redshift, type 1a supernovas, and cephid variable stars (for really nearby galaxies).
 
  • #10
robertm said:
Inertia still applies for EM radition, so i believe it depends entirely upon the environment into which you are shining the radiation. Since the majority of space is nearly a perfect vacuum EM radiation will countinue along its original vector until acted upon by an outside force ie... black hole, nebula, telescope ect. Someone please correct me if I am wrong.
Inertia is a property of mass, so it doesn't apply to light, but otherwise yes, it is similar to Newton's first law - if nothing gets in the way, it'll keep going essentially forever. The Hubble has taken pictures of objects 13 billion light years away.

http://hubblesite.org/newscenter/archive/releases/1997/25
 
  • #11
russ_watters said:
Most of those methods are highly accurate, especially since stars tend to fit a very tight band of types.

Note, though, that those methods are used for stars in our galaxy. For more distant stars/galaxies, they use redshift, type 1a supernovas, and cephid variable stars (for really nearby galaxies).

Oh right, well I wouldn't know
 
  • #12
russ_watters said:
Most of those methods are highly accurate, especially since stars tend to fit a very tight band of types.

Note, though, that those methods are used for stars in our galaxy. For more distant stars/galaxies, they use redshift, type 1a supernovas, and cephid variable stars (for really nearby galaxies).

they use the supernovae as a reference because of how much light it emits, right?
 
  • #13
robertm said:
... black hole, nebula, telescope ect.
And eyeballs: if a photon manages to travel anything like a billion trillion miles I'd rather catch it with my eye than a ccd.
 
  • #14
jobyts said:
How do the scientists conclude that the particular light we received is x years old?

Indirect methods. One way is to measure the redshift- how far a particular emission line has been skewed. The age of the universe is determined, in part, by the redshifted background radiation (the 4 K noise).

Another way, as russ mentioned, is using "standard candles". These are sources that we "know" emit a certain amount of light:

http://csep10.phys.utk.edu/astr162/lect/cosmology/cosmicd.html

Parallax measurements are good only for very close objects.
 

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