How can light from billions of years ago reach Earth?

[chazus]

Somehow you read the article, but didn't read the article.

This galaxy is very old, but didn't exist during the big bang. That means we had about 500 million years of the stuff that makes up our galaxy to move away from THAT galaxy, before it started producing light.

Think of it this way. You and a friend are outside. He has a battery, and a flashlight. He tells you "Go", and you start running from him. Meanwhile, he has to pull apart the flashlight, put the battery in, and put it back together before he shines it at you. The galaxy (or light) didn't exist during, or at the point of the big bang.

[Octopode]

No, it is "just" a theory because that's what explainations are called in science. It's not like it has some higher status than "accepted theory" to graduate into.

It is "just" a theory because it still cannot be conclusively proven under all circumstances to be absolutely correct.

Theories are accepted to be true and correct after enough analysis and observation, but if they were absolutely true they do "graduate" into facts. It simply doesn't happen much anymore because we have reached a point in most sciences that things cannot be proven to be absolute fact using current methods of testing and observation. Even a multi-sigma experimental result has a (very) small margin of error.

[Laize]

First off. The Big Bang is still just a theory. A widely accepted theory maybe, but still just a theory.

Holy shit... do people really still not understand what a "theory" is?

A theory isn't "a good idea" of how something works.

THIS is a fucking theory.

The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence. Many scientific theories are so well established that no new evidence is likely to alter them substantially. For example, no new evidence will demonstrate that the Earth does not orbit around the sun (heliocentric theory), or that living things are not made of cells (cell theory), that matter is not composed of atoms, or that the surface of the Earth is not divided into solid plates that have moved over geological timescales (the theory of plate tectonics)...One of the most useful properties of scientific theories is that they can be used to make predictions about natural events or phenomena that have not yet been observed.

[Annapolis]

It is "just" a theory because it still cannot be conclusively proven under all circumstances to be absolutely correct.

Theories are accepted to be true and correct after enough analysis and observation, but if they were absolutely true they do "graduate" into facts. It simply doesn't happen much anymore because we have reached a point in most sciences that things cannot be proven to be absolute fact using current methods of testing and observation. Even a multi-sigma experimental result has a (very) small margin of error.

There are scientific theories that are now facts? Who decides when they make this transition?

[Synthaxx]

The universe is still expanding. I'd even go so far as to say it's still in it's infancy. I say this because there are a great number of "areas" that are just gas and nothing else, and from what we know, have never been anything but gas. They're essentially forming new galaxies by drawing this gas in to form stars, much like our sun, and any rock and dust in there will be formed into planets over time. Sort of off topic, but related.

As others have said, light speed is actually distance and not time. A light year is how far light travels in 1 Earth year as we already know the speed of it; 299,792,458 Meters per second, or just under 300,000KM/s. In 1 hour, light will travel 1.08Bn KM. In 1 day, 26Bn KM. In 1 year [365 days], 9.4Tn (Trillion). For the furthest "object" ever seen (13.1Bn light years aware IIRC), the light has travelled 123.9St (Sextillion) KM. To explain that - Million < Billion < Trillion < Quadrillion < Quintillion < Sextillion. To put it into some real perspective, you would have to go around the Earth's Equator 4973641660471282361 (4.97 Quintillion) times.

So, we know the speed, and how fast it actually is and have some idea of just how far it is in distance. You probably realize now why i brought up "the universe is still expanding" point. If it's still expanding, it means that there's still things we won't see for many billions of years (as they don't exist yet). Once they have formed, they'll likely emit light (the star of a solar system will at least). Assume for a moment it's formed on the very edge of the universe and assume at that point, it's 15Bn Light years away. The light from this star will start on it's way to earth at 300,000KM a second. In 15Bn years, we'll see the first light of this star reach Earth. It'll be extremely red in colour, likely into the infrared wavelength (as space distorts light, and this particular example is known as redshift).

Our sun is a massive distance from Earth if we think in realistic values. However, it's only around 8 "Light Minutes" away from Earth. Despite such a great distance, we feel it's heat, see it's light, and rely on it's energy to survive. We don't feel the heat from other stars (at least not to the point we can say they're heating Earth), yet we see their light eventually. It just takes time.

[Warpaladin]

"Just a theory" wrongly implies that there is a higher status than theory in science. There isn't.

---------- Post added 2012-09-24 at 04:52 AM ----------


Space is expanding. In 50 billion years light from other galaxies would not reach Earth anymore.

Two problems with that :P Earth wont be here 50 billion years from now nor would our sun.

[semaphore]

It is "just" a theory because it still cannot be conclusively proven under all circumstances to be absolutely correct.

NOTHING can. And that also has nothing to do with being a scientific theory.

but if they were absolutely true they do "graduate" into facts.

They absolutely do not. Facts and theories are categorically different things. Hell, facts probably change more often than established theories.

[Garnier Fructis]

Space is expanding. In 50 billion years light from other galaxies would not reach Earth anymore.

Well, the Earth won't even be here in 50 billion years.

[Bathory]

How? Aliens.


/insertpictureofdudehere

[semaphore]

Well, the Earth won't even be here in 50 billion years.

It's just to demonstrate a point about the expansion of space... substitute "where Earth is now" in if you have to ><

[HolgerDK]

299,792,458 Meters per second, or just under 300KM/s

Its ~300 million m/s and not 300km/s, so you need 3 more zeros on that km/s speed

[Irisel]

Another way of going about it is, How can light that is 13 billion years old be seen by the Earth which itself only 4.5 billion years old?

Think about it like this. An old man is traveling a distance that will take him 13 years to make, and is traveling towards you. After 9 years of his travel, you come into existence. Right around the time of your 4th birthday, give or take, he reaches you.

The light from this super old galaxy was traveling for a long time before it reached Earth. It was traveling even before Earth was made; it just had a REALLY long time and distance to travel, despite coming into existence and most likely dying before out Sun or Earth was even made.

[Cerus]

How? Aliens.


/insertpictureofdudehere

If you're asking how the earth will be gone before 50 billion years it's because our sun will turn into a red giant in about 5 billion years when it runs out of hydrogen. When that happens all the inner planets will be engulfed by the expanding sun and the earth will cook.

Another way of going about it is, How can light that is 13 billion years old be seen by the Earth which itself only 4.5 billion years old?

That makes zero sense.

This is a little bit easier to explain if we talked about something else, like radio or television.

In the 1950's or whatever there was a TV show called I Love Lucy and it was broadcast all over the nation. Some of those broadcasts bounced off our planet and into space. Now somwhere out there is an alien civilization with a radio device that doesnt work quite right and are managing to pick up the signal and see the antics of psychotic man-apes from america playing out their comedy routine from circa 1950's. When they receive this signal is irrelevant, be it in 2012 or 3012, they are seeing the tv show from 1950's.

The signals don't "bounce off the planet" they simply shoot off into space as they aren't being sent in any particular direction. If they were then only certain people could pick up the signal. In fact humans have been unintentionally sending radio waves off into space for over a hundred years - long before TV signals started going out into space.

OP - think of it this way - that galaxy is over 7.75961975 × 1022 miles away. If traveling at the speed of light if would take you 13.2 billion years to get there. At the speed we can currently travel it would take you about 660,000,000,000,000 years to get there. You experience these delays all the time. Sonic booms and thunder is a great example since you often see the lighting strike and then hear the rumble moments later. Light travels much faster than sound so you see it before you hear it. The moon landing missions had to deal with a delay in all the transmissions and there's a few seconds delay on satellite TV signals at home vs cable. Hard to fathom the distances when you're so used to a few feet or a few hundred miles.

As for the big bang - current technology has allowed scientists to view space at only a few seconds after the big bang. Essentially seeing back in time as they do when looking at other distance stellar objects. There was a recent supernova that was observed however that sun went nova a loooong time ago. But again due to the distance it took that long before the light reached Earth.

[Garnier Fructis]

It's just to demonstrate a point about the expansion of space... substitute "where Earth is now" in if you have to ><

I know. Sorry, but it was just too good to pass up haha.

[AbsolutePitch]

I think you're not accounting properly for the size of the universe. The galaxy in question probably existed at a point in space that's beyond unimaginably far. Your question would be valid if the galaxy was closer to ours, or even a former generation galaxy of ours; we'd never be able to see light from our former gen stars or galaxy(ies), but someone in a galaxy billions of light years away might.

[tennesseej]

The answer is actually pretty simple. You are correct, light has a constant speed, and we have yet to discover anything that is moving faster than light.

One thing we do know (or at least think we know) is that the universe we can see is expanding. It is expanding in such a way, that everything is moving apart. We know this because everything we look at is "red-shifted", meaning the waves are stretching (if it was blue-shifted, the waves are being compressed, and the object would be moving towards us). You can think about it like using a marker to put dots on a balloon. As the balloon expands, all the dots are moving away from each other.

Now image 2 cars that start in a city. One car travels west at 50 miles per hour. The other car travels east at 50 miles per hour. After 1 hour, the cars 100 miles apart. That means, that if someone on the eastbound car was to try and throw a baseball at the other car, it would need to travel faster than 51 miles per hour to reach the other car, and it would take a really really long time (in this example, it would take 100 hours).

It's the same story with planets/stars/galaxies. If a galaxy is moving "east" at 0.75 times the speed of light (c), and we are moving west at 0.75c, it will take a really long time for the light to reach us, because light only has a 0.25c advantage on us, and we are moving at 0.75c. If we were traveling at faster than 1c, the light would never reach us, but we cannot travel faster than 1c, so eventually, all light will reach us (if the universe is non-infinite).

Light from this galaxy has been reaching us for a long time, we just didn't detect it until now.

[Mnevis]

the force of gravity, and the effects it has on matter is a well documented REAL force

Gravity is an observable phenomenon. Newton's mathematical formulation of the law describing it has a great amount of power in describing and predicting the world of classical mechanics we see around us. Similarly, the Big Bang theory of the universe has support from well documented real observations and predictions. The cosmic background radiation is not nearly as accessible to our minds as the moon and earth's orbits, but that's not science's fault.

On-topic, yeah it's because we (the density of matter that would eventually form our local cluster of galaxies, the Milky Way, Sol and her solar system, and me and you) were already a ways away from this galaxy when it formed, cause of all the antimatter exploding or something. Since then, we've been booking it away from that galaxy's then-location in space (the space between has been expanding) and the light has been catching up to us, it just started its journey a really really long time ago.

It's all kinda mind-boggling.

[Vonwulf]

Some of you guys are reding it wrong. The article stated that the object was 13,2 billion OLD, wich means that the light we see now was emitted 13,2 billion years ago. Lightspeed is not constant, only in a vaccum. The question is still valid, since im guessing that the OP meant the the light from 13,2 billion years ago should have passed us a long time ago unless we at some point were traveling away from each other faster than the speed of light.
And just as someone before staded: at the beginning of time space and time did NOT act as we know it now.

"It's the same story with planets/stars/galaxies. If a galaxy is moving "east" at 0.75 times the speed of light, and we are moving west at 0.75 times the speed of light, we will never see light from that galaxy because we are moving apart at 1.5 times the speed of light."
Its just wrong. At any given moment that any of the galaxys stated above is emitting light towards the other galaxy that light is traveling towards the other galaxy at lightsspeed regardless of the speed fo the galaxy that emitted the light.

[Mnevis]

Light can be moving at light-speed and not be able to catch up to another galaxy (but yeah, you're right, it will catch up with a galaxy moving at .75c).

According to our current understanding, at some point in the future, beings living in whatever exists of the Milky Way won't be able to tell that there are or ever were other galaxies.

[det]

This is a little bit easier to explain if we talked about something else, like radio or television.

In the 1950's or whatever there was a TV show called I Love Lucy and it was broadcast all over the nation. Some of those broadcasts bounced off our planet and into space. Now somwhere out there is an alien civilization with a radio device that doesnt work quite right and are managing to pick up the signal and see the antics of psychotic man-apes from america playing out their comedy routine from circa 1950's. When they receive this signal is irrelevant, be it in 2012 or 3012, they are seeing the tv show from 1950's.

...and an alien civilisation that looked into space onto earth, but is 65 million lighyears away would not see man, but dinosaurs?