Big Bang: Expansion Accelerating

[Grayman]

Against all known facts about gravity and space the universe's expansion is suggested to be accelerating according to scientists. Why?

Consider that the greatest redshift is occurring between our galaxy and a galaxy of the most distant past while less redshift is occurring between our galaxy and one of not so distant past. The greater redshift means a greater rate of travel apart. So If our galaxy is traveling apart from other galaxies at a slower rate currently than it was in the past the expansion must be 'de-accelerating'.

Also keep in mind that expansion is considered uniform so that all bodies move apart.

Just using random numbers but this should put it in perspective...

OurGalaxyTravel + CloseGalaxyCloseTimeAndDistanceTravel = 600km/s 5 billion years ago Smaller Redshift
OurGalaxyTravel + FarAwayGalaxyTimeAndDistanceTravel = 1600km/s 13 billion years ago Larger Redshift


Speed of separation was greater in the past than current, therefore separation has slowed.

What am I missing or misinterpreting? Why are they creating a 'dark matter' just to make the numbers fit instead of considering they made a mistake?

 

[Pyropyro]

Re: Big Bang: Expansion Accellerating

Against all known facts about gravity and space the universe's expansion is suggested to be accelerating according to scientists. Why?

Consider that the greatest redshift is occurring between our galaxy and a galaxy of the most distant past while less redshift is occurring between our galaxy and one of not so distant past. The greater redshift means a greater rate of travel apart. So If our galaxy is traveling apart from other galaxies at a slower rate currently than it was in the past the expansion must be 'de-accelerating'.

Also keep in mind that expansion is considered uniform so that all bodies move apart.

Just using random numbers but this should put it in perspective...

OurGalaxyTravel + UknownGalaxyCloseTimeAndDistanceTravel = 600km/s 5 billion years ago Smaller Redshift
OurGalaxyTravel + UknownGalaxyCloseTimeAndDistanceTravel = 1600km/s 13 billion years ago Larger Redshift


Speed of separation was greater in the past than current, therefore separation has slowed.

What am I missing or misinterpreting? Why are they creating a 'dark matter' just to make the numbers fit instead of considering they made a mistake?

Grayman, what is your opinion on the current prediction model where the Big Bang and Big Crunch may not be part of the Universe's timeline at all?

Layman article: http://phys.org/news/2015-02-big-quantum-equation-universe.html
Actual article: http://www.sciencedirect.com/science/article/pii/S0370269314009381

 

[Black Rose]

Re: Big Bang: Expansion Accellerating

http://youtu.be/DI_OZZ_G4SI

 

[Ex-User (11125)]

Re: Big Bang: Expansion Accellerating

What am I missing or misinterpreting? Why are they creating a 'dark matter' just to make the numbers fit instead of considering they made a mistake?

im not well read enough on redshift to give a good answer to your questions but i share the same speculation

if the universe was much denser in the past how did expansion start? i mean when we look local space contraction happening now or how local gravities attract eachother then the universe should have collapsed on itself right? so why did it start to accelerate instead of collapse? yeah dark matter conveniently answers that. its weird how a theory that involves 96% imaginary stuff we cant even detect is still so prevalent...im open to different theories/hypotheses but this one should go back to planning stage imo

 

[Pizzabeak]

Re: Big Bang: Expansion Accellerating

Well for one, I too wondered why they assumed the proposed Universe expansion would slow down so as to possibly close in on itself. If gravity attracts things wouldn't the apparent force get weaker as expansion occurred? Thus, wouldn't matter get further apart so as to isolate gravitation and allow expansion to exceed it? They assumed from a Big Bang standpoint that any acceleration would naturally slow down maybe before matter got too far apart. On a local standpoint some objects are close enough for possible collisions but in general on a large scale galaxies are moving away from each other.

Not exactly sure where this came from: "So If our galaxy is traveling apart from other galaxies at a slower rate currently than it was in the past the expansion must be 'de-accelerating'."

I think the redshift is smaller simply because they are closer. This is basically going on in every direction and from any galaxy in the universe. Depending on the rate of expansion of the radius other galaxies would recede with a speed in proportion to it. Some of the original models (such as the big crunch scenario) didn't really predict an expansion which would be speeding up though.

All dark and other forms of exotic matter do is add extra mass to figures. There was a certain critical density the universe needed in order to cease expansion and begin contracting. When they tried to add up all the mass of known stuff the amount turned out smaller than expected to account for certain motions. One example is that it seemed certain stars move at higher velocities than expected based on their gravitational conditions. Thus, they assumed there must be extra matter that is unobservable but able to exert gravity, partially due to possible mass. Even when accounting for this the amount of mass in the universe was too little to agree with certain models. Certain candidates for this exotic matter are types of particles, like decaying neutrinos, which would probably be concentrated in abundance.

I believe considering this, the universe must have had a particular shape, as certain characteristics were observed despite the overall shape of the universe. Apparently, the galaxies farthest away have a redshift which is greater than that predicted with Hubble's constant. This, then, is due to a repulsive force which is opposite gravity. One popular example might be that of a rubber band, which when stretched actually creates a tiny anti-gravitational force via "tension" (rather than pressure), however, of course, on Earth and due to the rubber band, this field is weak enough so that gravity can easily overtake it. Similar to how gravity increases via distance decreasing, the weak repulsive force increases via distance increasing. When put in the context of receding galaxies this is known to be caused by dark energy, which acts opposite that of dark matter considering the exotic matter is known to add mass and therefore gravitational attraction. The structure of this is typically unknown.

I need to get caught up on all the latest developments. Oddly enough, if I'm not mistaken, this is akin to the cosmological constant Einstein added which suggested a stable universe. A few years after general relativity I think he actually assumed an eternal universe with no beginning of time.

 

[Lazy Vulpes]

Re: Big Bang: Expansion Accellerating

Wikipedia says:

Spoiler

In order to calculate the redshift one has to know the wavelength of the emitted light in the rest frame of the source, in other words, the wavelength that would be measured by an observer located adjacent to and co-moving with the source. Since in astronomical applications this measurement cannot be done directly, because that would require traveling to the distant star of interest, the method using spectral lines described here is used instead. Redshifts cannot be calculated by looking at unidentified features whose rest-frame frequency is unknown, or with a spectrum that is featureless or white noise (random fluctuations in a spectrum)

This to me suggests that scientists are already accounting for the difference in time between celestial objects when doing their measurements, and come to the conclusion that space is expanding at an accelerating rate through time. So while your logic holds true, your assumption of how the measurement was taking may be wrong.

 

[SpaceYeti]

Re: Big Bang: Expansion Accellerating

Let's say we have sss. Now, every t, an s doubles. Thus, after one t, we have ssssss. After one more t, we have ssssssssssss. Then, ssssssssssssssssssssssss. Notice how, if we began measuring our s from the leftmost s to the rightmost s, The farther s seems to be accelerating away.

If space can expand, which it can, we witness it happening, then this would be the case with points within it. It's not that expansion is accelorating, it's that the farther there is between two points, the more space there is between them to expand a proportionally similar distance.

Maybe gravity is the effect of masses not expanding with the space containing them.

 

[Pizzabeak]

Re: Big Bang: Expansion Accellerating

There's a fair amount of uncertainty regarding the distances to galaxies as well as rate of expansion, yes.

 

[Grayman]

Re: Big Bang: Expansion Accellerating

Let's say we have sss. Now, every t, an s doubles. Thus, after one t, we have ssssss. After one more t, we have ssssssssssss. Then, ssssssssssssssssssssssss. Notice how, if we began measuring our s from the leftmost s to the rightmost s, The farther s seems to be accelerating away.

If space can expand, which it can, we witness it happening, then this would be the case with points within it. It's not that expansion is accelorating, it's that the farther there is between two points, the more space there is between them to expand a proportionally similar distance.

Maybe gravity is the effect of masses not expanding with the space containing them.

Good answer. Now I have to think how the difference in time fits into this...

 

[Methodician]

Re: Big Bang: Expansion Accellerating

Now I'm no physicist but I think you're overlooking a very simple explanation...

There is more space expanding between us and more distant bodies. THAT"S IT!

If you're relatively close to a celestial body, the amount of space expanding between you and it is not so great, so it's not moving away as fast. If you're relatively far from a celestial body, the amount of space expanding between you and it is great, so it's moving away much faster!

Am I missing something?

 

[Ex-User (11125)]

Re: Big Bang: Expansion Accellerating

what i dont get about the more space=more expansion explanation is how can this explain how space began to expand long ago when the universe was -smaller-(for lack of a better word) i mean if expansion is too small to measure on a scale smaller than billions of light years, and the attractive forces can easily overcome this so that close matter will not be getting blown apart...then how did it begin to expand?
(sorry if this is a dumb question)

 

[Lazy Vulpes]

Re: Big Bang: Expansion Accellerating

Condensed energy from a quantum soup of possibilities?

 

[Grayman]

Re: Big Bang: Expansion Accellerating

what i dont get about the more space=more expansion explanation is how can this explain how space began to expand long ago when the universe was -smaller-(for lack of a better word) i mean if expansion is too small to measure on a scale smaller than billions of light years, and the attractive forces can easily overcome this so that close matter will not be getting blown apart...then how did it begin to expand?
(sorry if this is a dumb question)

I don't get how such a thing as emptiness can expand anyways. It is physically impossible.

 

[Lazy Vulpes]

Re: Big Bang: Expansion Accellerating

I don't get how such a thing as emptiness can expand anyways. It is physically impossible.

General relativity?

 

[computerhxr]

Re: Big Bang: Expansion Accellerating

There is more space expanding between us and more distant bodies. THAT"S IT!

If you're relatively close to a celestial body, the amount of space expanding between you and it is not so great, so it's not moving away as fast. If you're relatively far from a celestial body, the amount of space expanding between you and it is great, so it's moving away much faster!

Am I missing something?

This makes sense to me. It all depends on how you look at it.

Condensed energy from a quantum soup of possibilities?

Exactly what I was thinking. Nothing can be so many different things. We just don't understand it or have a way to see what's the next layer deep --- yet! However, then we will discover another layer deep, then another, and so on.

...

That was a good video. I seems like this is how a lot of people feel but lack the technology or the education to figure out in the past. Now we have computers and the internet. I feel like we should go back over everything with a new perspective and see what else could be discovered. Thanks for posting this.

 

[Pizzabeak]

Re: Big Bang: Expansion Accellerating

I don't get how such a thing as emptiness can expand anyways. It is physically impossible.

Based off what? The more room there is the more space there would be. Imagine a bottle. Space isn't really empty anyway. There's probably minute fluid like perturbations interspersed throughout it in a uniform like manner.

Of course, that's only based off the leading considerations. As has been highlighted, what if someone decided to alter the descriptions of space-time or of the cosmos? Or of life in general? I wouldn't be surprised if someone thought most of it to be nonsense. Say the universe is a simulation. Um... Would there be much need for all this?

 

[StevenM]

Re: Big Bang: Expansion Accellerating

Consider that the greatest redshift is occurring between our galaxy and a galaxy of the most distant past while less redshift is occurring between our galaxy and one of not so distant past closer to us.

Not that I'm 100% sure but:

I think the red-shifting effect is like the sound of a car. A car engine heard from farther away has less high-frequency pitches, than a car that is closer.

Car that is close: "eeeeeeeeeeeeeee"
Car that is far away: "ooooooooooooooo"

Something travelling at high frequency oscillation needs a lot more energy to travel than lower frequencies. At larger distances, I think the higher frequencies lose energy, or at least have better chances of scattering or getting obstructed by something.

I didn't think the 'red' came from them actually moving away, just that they are farther away.

Differences in energy of a certain bandwidth over time could probably estimate their acceleration. <- 'Red-shifting'

The greater redshift means a greater rate of travel apart. So If our galaxy is traveling apart from other galaxies at a slower rate currently than it was in the past the expansion must be 'de-accelerating'.

Also keep in mind that expansion is considered uniform so that all bodies move apart.

I don't think the expansion was considered uniform.

I thought I read that it was considered that gravity hinders expansion. The closer two objects are, and the more gravitational effect they have on each other, the less they expand from each other.

I think in a simplified way, it can be considered:

Rate of expansion is proportional to distance apart.

^more expansion makes more distance. And more distance makes a faster rate of expansion.

Thus the distance between our earth and the sun (let's say) is hardly expanding at all. The gravity of our sun is holding us with it pretty strongly.

And the distance between us and the nearest star may be expanding just a wee bit more, (because we are farther apart), but still not much to worry about.

Though, the distance between two galaxies can be immense. Gravity between the two galaxies has much less of an effect, thus they may be expanding further apart quite quickly. (And gaining speed because more distance makes faster expansion). Things that are together will likely stay together, while things that are apart, will get even more further apart. (Depending on gravitational effect).


***************************

It's not a good idea to compare the amount 'redshifting' between something that is far, and something that is near.

Acceleration can be seen when:

Today: Redshifting between us and galaxy 'x' is happening at units per time.
Tommorow: Redshifting between us and the same galaxy 'x' is happening at a greater rate of units per time.

Thus, it is accelerating.

 

[Grayman]

Re: Big Bang: Expansion Accellerating

Based off what? The more room there is the more space there would be. Imagine a bottle. Space isn't really empty anyway. There's probably minute fluid like perturbations interspersed throughout it in a uniform like manner.

Of course, that's only based off the leading considerations. As has been highlighted, what if someone decided to alter the descriptions of space-time or of the cosmos? Or of life in general? I wouldn't be surprised if someone thought most of it to be nonsense. Say the universe is a simulation. Um... Would there be much need for all this?

It is never the space that changes only the items around it.

 

[Grayman]

@TMills

I am 100% certain redshift indicates speed and not distance. The photon is ejected out of it's source at the speed of light in relation to its source and since the source is traveling away from us at a large speed the photon is moving slower than our light normally would. This slower photon looks redder because the photon is moving more slow and the wavelength is being streched out.

 

[Ex-User (11125)]

Re: Big Bang: Expansion Accellerating

It is never the space that changes only the items around it.

I searched on google and found this thread( https://www.physicsforums.com/threa...xpand-reality-behind-the-gr-equations.176380/ ), the op asks the same question and there are lots of good responses especially the one by marcus

 

[StevenM]

@TMills

I am 100% certain redshift indicates speed and not distance. The photon is ejected out of it's source at the speed of light in relation to its source and since the source is traveling away from us at a large speed the photon is moving slower than our light normally would. This slower photon looks redder because the photon is moving more slow and the wavelength is being streched out.

Yes, you are right. I apologize.

 

[SpaceYeti]

Re: Big Bang: Expansion Accellerating

what i dont get about the more space=more expansion explanation is how can this explain how space began to expand long ago when the universe was -smaller-(for lack of a better word) i mean if expansion is too small to measure on a scale smaller than billions of light years, and the attractive forces can easily overcome this so that close matter will not be getting blown apart...then how did it begin to expand?
(sorry if this is a dumb question)

It doesn't. That's a different question.

 

[Pizzabeak]

On a revolving body the side moving away from us appears more to the red while the side moving towards us produces light more blueshifted. Redshift can still correspond with distance.

 

[SpaceYeti]

@TMills

I am 100% certain redshift indicates speed and not distance. The photon is ejected out of it's source at the speed of light in relation to its source and since the source is traveling away from us at a large speed the photon is moving slower than our light normally would. This slower photon looks redder because the photon is moving more slow and the wavelength is being streched out.

Actually, the lightwave is redshifted both by objects moving away and cosmological expansion. Because cosmological expansion is increased steadily the farther away something is, you can use it to determine distance and speed.

 

[Fat Bread]

@TMills

I am 100% certain redshift indicates speed and not distance. The photon is ejected out of it's source at the speed of light in relation to its source and since the source is traveling away from us at a large speed the photon is moving slower than our light normally would. This slower photon looks redder because the photon is moving more slow and the wavelength is being streched out.

While the gist of what you said here as it relates to the discussion is correct, I think it's important to point out that the photon is NOT moving slower, and in fact no photon ever moves faster or slower than the speed of light. The individual photons emanating from a distant galaxy travel just as fast as those coming at us from a much closer one. The rate at which individual photons reach us, however, is less for those coming from the distant galaxy.

In other words, if we set up two photon detectors, one pointing at a nearby galaxy and another at a distant galaxy, we might find that we receive 5000 photons per second from the nearby galaxy while the distant galaxy appears to shoot only 1000 photons per second at us. In reality, both galaxies are throwing out photons at the same rate, but because one of them is moving away from us very quickly, the distance (or wavelength) between it's photons is much greater from our vantage point. By the way, 1000 and 5000 were chosen arbitrarily, and most likely don't accurately represent the actual photon rates that would be measured in such an experiment. The fact that the rate would be higher for a closer galaxy as opposed to a distant one is accurate, however.

 

[SpaceYeti]

There's actually two effects to consider there, too. As you pointed out, because one galaxy is moving away from us at a faster rate (due to being farther away to begin with), we receive fewer of it's photons per second. However, the predominant effect which would reduce that amount would be the cubed square law.

Also, the universe stretching out along the path of the photon is half of the reason for the red shift, as it's frequency is reduced the more expanding universe it travels through.