why is it said that the objects on the other side of the big bang's light wont reach

[Onceler]

us?
I would think that eventually they would.

 

[JTsyo]

Since the space between them and us is expanding faster than the speed of light.

 

[Sunny129]

to elaborate on the answer above, the Hubble Constant, or the rate at which the universe (or more appropriately, spacetime) expands, shows us why we can't (and never will) see the light you speak of. while the Hubble Constant has not been calculated exactly, i think its safe to assume a value of 70 km/s/Mpc (kilometers per second per Megaparsec), as that value is more than adequate to demonstrate that light beyond a certain distance from us will never reach us. first consider that a parsec is approx. 3.26 light years, so a Megaparsec is 3.26 million light years. the most distant light we can see is approx. 13.7 billion (or 13,700 million) light years away. divide it by a Megaparsec (or 3.26 million light years), and we see that 13.7 billion light years is equal to approx. 4,200 Megaparsecs. well if the Hubble Constant says that spacetime expands at a rate of ~70 km/s/Mpc, then objects 1 Megaparsec away from us should be receding from us at a rate of 70 km/s, objects 2 Megaparsecs away from us should be receding from us at a rate of 140 km/s, and so on and so forth. extrapolate that rate of recession to objects at the edge of the visible universe, ~13.7 billion light years (or 4200 Megaparsecs) distant, and you'll see that objects at that distance are receding from us at a rate of 294,000 km/s, or 0.98c (98% of the speed of light).

now obviously we have to allow for some imprecision in the Hubble Constant value we used, but it is uncanny how close our calculations came to the speed of light, and there's a reason for that. suppose we wanted to know the rate of recession of objects 15 billion light years away. in reality we can't see them b/c they are beyond the edge of the visible universe. but simple math tells us that 15 billions light years equals ~4600 Megaparsecs, which corresponds to a recession rate of 322,000 km/s, or 1.073c. since we know light cannot travel faster than 300,000 km/s, or 1c, we know that light coming from objects 15 billion light years away cannot outpace the expansion of spacetime itself, and will therefore never reach us.

 

[Onceler]

I mean at first everything was moving away faster than the speed of light but then slowed down long enough for galaxies to form and is now moving away faster again.
Wouldn't some light get through if the other side slowed down as well?

 

[Sunny129]

I mean at first everything was moving away faster than the speed of light but then slowed down long enough for galaxies to form and is now moving away faster again.
Wouldn't some light get through if the other side slowed down as well?

i suppose so, but you have to remember that the inflationary period of the universe that you're referring to started and ended within the first second after the Big Bang occurred...so if there was a period during which light could have traversed the known Universe, it would have been over 13 billion years ago, before our planet, our sun, and perhaps even the Milky Way was formed. if we were around then, i suppose we would have seen that light from the other side of the universe...but we weren't. and due to the fact that the universe has been expanding an an ever increasing rate since then, it is no longer possible to even hope to see light from objects more distant than ~13.7 billion light years.

 

[ZeroRift]

How does this work out with special relativity?

If it's impossible for objects to exceed the speed of light, then wouldn't it follow that light from distant sources would reach us eventually no matter what %c they were traveling at?

Also, isn't the speed of light emitted by an object constant regardless of how fast that object is moving? It's my understanding that observers traveling in opposite directions at 0.6c can still see eachother, but I haven't reviewed that math in years....

Under those assertions, objects 14 billion light years away would still be visible so long as they were emitting light 14 billion years ago.

 

[Revolution 11]

Objects can not exceed the speed of light but this applies to galaxies, stars, etc. Spacetime is not really a object and so can expand faster than the speed of light. A object can expand away from any given view point "faster" than speed of light.

Consider this. The "universe" may be much bigger than 13.7 billion light-years. Well, we know it is since with the rate of expansion, a object 13.7 billion light-years away when the light was emitted would now be roughly 40 billion light-years away since the expansion is still ongoing.

So if the universe is bigger than a sphere with the radius of 13.7 billion light-years, what's to say that a observer at the edge of our observable universe (13.7 billion light-years) doesn't have his own observable sphere of similar distance.

I am not sure I am getting my point across but space is really freaking large. Concerning the Big Bang, even if we were present on "one side" of the universe as it expanded, the expansion is faster than the speed of light. So even if the pre-Big Bang universe is only 1 inch in diameter with two people on either end, they would never see each other after the expansion started. The light would move towards each other, but the universe would expand faster. This doesn't violate relativity because from either observer's point of view, they are standing still (relatively) but they don't see the other observer.

Someone more knowledgeable please tell me if I am just spouting nonsense here?

 

[Sunny129]

If it's impossible for objects to exceed the speed of light, then wouldn't it follow that light from distant sources would reach us eventually no matter what %c they were traveling at?

you have to keep in mind that the objects/light sources in question are not physically moving through space away from us at speeds greater than c...rather the spacetime between those objects/light sources and us is expanding at such a rate that, if one were able to stand outside our universe and look back in, it would appear as though certain objects/light sources that are farther than 13.7 billion light years apart are moving away from each other at greater than the speed of light. obviously an observer would have to exist in a universe of 4 or more spatial dimensions in order to stand outside our universe of 3 spatial dimensions and observe such a phenomenon...in other words, apparent velocities in excess of c in 4 spatial dimensions doesn't necessarily correspond actual velocities in excess of c in our universe of 3 spatial dimensions...

if this is not clear, i can try to elaborate on it more...but as you probably already knew, topics like these are extremely difficult to put into laymans terms, let alone into words period.

Also, isn't the speed of light emitted by an object constant regardless of how fast that object is moving?

yes, this is true.

Under those assertions, objects 14 billion light years away would still be visible so long as they were emitting light 14 billion years ago.

yes, but only b/c these assertions don't take into account the expansion of the universe and the fact that spacetime itself is not matter, as Revolution 11 mentioned above...

 

[ZeroRift]

Ah, by "space" I thought he was referring to distance, rather than the fabric of reality/spacetime. That definitely makes more sense, as space is not conserved in the presence of matter.

Now I'm curious: do we have any evidence to support the idea that space is expanding other than the limitation in how far we can see? What other observable phenomenon support this? (if you have a good source on this, I'd love to read it! For now, I'm headed to wikipeida....)

The idea that space itself is expanding along with the rest of the universe also implies that space was either emitted with matter at the beginning of the universe, or is being "pulled" by matter as it rushes away from the origin point.

 

[ericloewe]

Now I'm curious: do we have any evidence to support the idea that space is expanding other than the limitation in how far we can see? What other observable phenomenon support this? (if you have a good source on this, I'd love to read it! For now, I'm headed to wikipeida....)

The idea that space itself is expanding along with the rest of the universe also implies that space was either emitted with matter at the beginning of the universe, or is being "pulled" by matter as it rushes away from the origin point.

Space is expanding (or at least stars are drifting apart) because we can observe the Doppler effect in the light from distant stars - the color of the light tends toward red, indicating a longer wavelength, which means distance is increasing.

 

[ZeroRift]

Redshift does not require space to be expanding, it only requires that an object's relative velocity be non-zero.

Inversely, the intermediate dimensionality of spacetime between two objects does not have to change in order for the universe to expand (and therefore in order to observe redshift).

To simplify: Redshift simply means the observed object is moving away from you. It does not have any bearing on how the object is being moved.

 

[Sunny129]

Redshift does not require space to be expanding, it only requires that an object's relative velocity be non-zero.

Inversely, the intermediate dimensionality of spacetime between two objects does not have to change in order for the universe to expand (and therefore in order to observe redshift).

To simplify: Redshift simply means the observed object is moving away from you. It does not have any bearing on how the object is being moved.

while the above points are irrefutable facts, the very nature of the particular "Doppler" effect being studied does have bearing on how objects both nearby and at cosmological distances are being moved. as Edwin Hubble looked at light sources increasingly farther away, he noted that their light was increasingly red-shifted. now, either every object at cosmological (non-gravitationally bound) distances is literally moving through spacetime away from us by coincidence, or spacetime itself is expanding over cosmological distances. what's more likely?

i understand that i didn't just prove the expansion of the universe lol...and i'm certainly no expert on the subject. but there is much more evidence than i know of that suggests that the Expanding Universe model is most likely the correct one, and the Cosmological Redshift is a direct result of this expansion. you might want to read some Timothy Ferris material...search him on amazon.com.

 

[Mark R]

Redshift does not require space to be expanding, it only requires that an object's relative velocity be non-zero.

Inversely, the intermediate dimensionality of spacetime between two objects does not have to change in order for the universe to expand (and therefore in order to observe redshift).

To simplify: Redshift simply means the observed object is moving away from you. It does not have any bearing on how the object is being moved.

True. However, observed redshift is directly proportional to distance from us +/- a small amount of noise, which can be related to random motion of the objects being examined. Broadly speaking, examination of multiple objects within a region (e.g. different regions of a galaxy) causes the random component to average out, and a reasonably precise linear relationship remains.

One explanation for this is that spacetime is curved (in other words, the fabric of space expands with time). Another, but somewhat less satisfactory explanation is that we are at the exact center of the universe, and for some reason, everything is moving away from us.

The other reason why an a curved spacetime is the current preferred idea, is that this idea necessarily follows from the solution of Einstein's field equations of general relativity.

 

[SMOGZINN]

Another, but somewhat less satisfactory explanation is that we are at the exact center of the universe, and for some reason, everything is moving away from us.

Not only that, but that things farther away from us are moving away faster then things closer to us, with there being a direct and exponential relationship to their distance to us and their velocity away from us.

 

[Biftheunderstudy]

There are a few points to be made here. Without a proper explanation to them, these might get you pointed in the right direction.

Our best evidence for Big Bang / Expanding Universe / Inflation is WMAP which measures the cosmic microwave background radiation. Most of the analysis comes from measuring the spatial variations in intensity (temperature), but a good chunk comes from the "Angular Power Spectrum" (Fourier Transform of the 2 point correlation function). This is how we measure things like Hubbles constant to a couple of decimal places, the amount of matter/dark matter in the universe, and the curvature of space time. To my knowledge, some good evidence that we are on the right track are the baryonic acoustic oscillations. It is very hard to explain these outside of a Big Bang with inflation universe.

Up to this point, the explanation of the expanding universe moving faster than c setting our particle horizon is exactly right. The only reason the rough calculation was "off" was that it was rough. The values from WMAP will set it by definition to be the same, i.e. age of the universe combined with Hubble's constant will work out to the same value (with some other higher level cosmology sprinkled in).

Some occum's razor type arguments might include:
The Horizon Problem
The Flatness Problem

Now, to completely asplode your brain, the universe is not simply expanding. Its also expanding at an increasing rate suggesting an energy source -- Dark Energy.

 

[silverpig]

Redshift does not require space to be expanding, it only requires that an object's relative velocity be non-zero.

Inversely, the intermediate dimensionality of spacetime between two objects does not have to change in order for the universe to expand (and therefore in order to observe redshift).

To simplify: Redshift simply means the observed object is moving away from you. It does not have any bearing on how the object is being moved.

Not necessarily. Two objects can be locally stationary and yet have a redshift w.r.t. each other. No motion is necessary if space expands.

 

[Ferzerp]

Technically, the light would get here with massive redshift.

You can't break the speed of light by saying object a is moving one direction at .9c and object b is moving the other direction at .9c so they are moving apart at some number larger than 1c. It won't work. No exceptions. Other variables change to accomodate this (such as distance, frequency/time, etc).

Functionally, there is no such thing as >1c, and if your argument/explanation/model relies on it, or ever references it, you're missing something.


Two objects can never move apart at 1c or greater.

 

[ZeroRift]

You're right, but this is exactly why these theories exist: to explain why objects appear to be moving faster than c. The answer is that space is expanding between the two points, not that the sum of their geometric velocities has exceeded c. (see post #8)

In other words, the objects are not exceeding c. Space is expanding at a rate such that light could never traverse the distance.

 

[ZeroRift]

Not necessarily. Two objects can be locally stationary and yet have a redshift w.r.t. each other. No motion is necessary if space expands.

That is an interesting notion. This implies that either:
A) Spacetime is directly altering the frequency of light that traverses "expanding" regions of space
B) The expansion of space "stretches" light contained inside, causing wavelength to increase

Now, to completely asplode your brain, the universe is not simply expanding. Its also expanding at an increasing rate suggesting an energy source -- Dark Energy.

That is one possible explanation for the acceleration that has been observed. Consider, instead: Space expands at some ideal rate in the absence of matter. As objects move farther apart, the rate of expansion of space between them approaches this ideal rate in proportion to their distance from each other (or perhaps in proportion to the change in distance between them). As a result, no energy source is needed as the objects are not actually accelerating. This would also explain why Hubble's Law has not been observed in systems that are gravitationally bound (IE: where objects are held close together by an outside force).

Further speculation:

Given that A) space is expanding, B) space is not conserved in the presence of matter and C) space can expand at a rate such that light cannot escape it, one must consider if gravity itself is a result of curved space. If matter dampens the rate of expansion of space (assumed from above), then in locations where there is a great deal of matter, one would expect that the space closer to the object should be "smaller" than the space that is far away from the object. In the extreme case of a black hole, the space just outside the event horizon would be expanding so quickly relative to the space within the event horizon, that light could not traverse the distance. Light, then, could be thought of as having no mass, as all of its observed behavior could be explained with the curvature of space (I believe).

Thoughts?

 

[Sunny129]

those are indeed some profound thoughts...but these thoughts aren't entirely original, and because of that, some of your assertions are already known facts. for instance:

Given that A) space is expanding, B) space is not conserved in the presence of matter and C) space can expand at a rate such that light cannot escape it, one must consider if gravity itself is a result of curved space.

it is currently generally accepted that gravity is in fact a direct result of the curvature of spacetime.

Light, then, could be thought of as having no mass, as all of its observed behavior could be explained with the curvature of space (I believe).

though there are some who will debate this, it is also currently generally accepted that photons of light carry no mass.

...don't be discouraged though. keep in mind that you very basically deduced (or at least theorized) some of these concepts on your own...even if you might have used some incorrect reasoning to get to the correct result, not many people have enough of an imagination to get that far. besides, that's how new theories are proposed and science progresses.

 

[ZeroRift]

rofl - Well, it's not the first wheel I've re-invented.

Knowing I'm not the first one to come up with this simply means I'm on the right track.

 

[Revolution 11]

it is currently generally accepted that gravity is in fact a direct result of the curvature of spacetime.

Now I thought that the curvature of spacetime was a result of gravity instead of the way you describe it. Or is it the mass of objects that causes the curvature in spacetime, which shows itself as gravity?

 

[Sunny129]

Now I thought that the curvature of spacetime was a result of gravity instead of the way you describe it. Or is it the mass of objects that causes the curvature in spacetime, which shows itself as gravity?

you hit the nail on the head - the presence of mass causes a curvature in spacetime, which then manifests itself as gravity in our universe. if an observer could be "outside looking in"...that is, if he or she could momentarily step out of our universe of 3 spatial dimensions, and into a space consisting of 4 spatial dimensions, he or she would literally be able to see the curvature of our 3-dimensional space. but since its impossible for us 3-dimensional beings to exist in a world of 4 spatial dimensions, we'll never directly "see" that curvature in the classical sense of being able to see. but we do know that gravity is the manifestation of this curvature.

 

[Mark R]

That is an interesting notion. This implies that either:
A) Spacetime is directly altering the frequency of light that traverses "expanding" regions of space
B) The expansion of space "stretches" light contained inside, causing wavelength to increase

That's basically it.

Photons that are 'in-flight' have their wavelength stretched as space-time itself expands.

So, if during the course of a photon's flight, space expands by 1%, the photon's wavelength will expand by 1%.

This gives a redshift that is directly proportional to distance, assuming that the metric expansion of space-time is constant.

 

[Revolution 11]

I understand how space is stretching between long distances. But is this a constant phenomena? Does light stretch even on short distances like from a campfire's light to the observer's eyes? I am assuming that this stretching is undetectable to most sensors.

Ahh, I hate relativity-based principles! I read and read up on you and I forget all the information by the end of the week. Good old Newtonian physics, how I miss you.