Why is the universe expansion accelerating?

[Hedges]

Even on a much simpler topic like, "The expansion of the universe is accelerating!", there seems to be near 100% consensus on that, and astrophysicists are trying to find the dark energy driving its acceleration.

But I have yet to see an explanation which shows how they have determined there is acceleration. What I have seen, doesn't.

 

[Bob B]

Even on a much simpler topic like, "The expansion of the universe is accelerating!", there seems to be near 100% consensus on that, and astrophysicists are trying to find the dark energy driving its acceleration.

But I have yet to see an explanation which shows how they have determined there is acceleration. What I have seen, doesn't.

Yeah .... it's too simple to spend any time on that one .....

 

[svetz]

Even on a much simpler topic like, "The expansion of the universe is accelerating!", there seems to be near 100% consensus on that, and astrophysicists are trying to find the dark energy driving its acceleration.

But I have yet to see an explanation which shows how they have determined there is acceleration. What I have seen, doesn't.

The expansion theory seems pretty solid. Back in the beginning of the 20th century (1909?) there was the big bang theory and the idea the galaxies would collapse back together then explode outwards again; or just drift farther away until gravity was to weak. The big question of the day was if the universe was open or closed, how long would it be before the next big bang, and how many times had it happened earlier. Even it the univers was "open" (e.g., no big bang) at least gravity would slow the expansion down.

So they took all sorts of images with telescopes. When the hubble space telescope went on line they measured it again. To their shock and horror, all those galaxies are accelerating away from each other. Being scientists, they coined dark energy to account for the energy needed for this anti-gravity. Personally, I don't believe in dark energy, a much more reasonable explanation to me is that space is being stretched and distorted by the galaxies spinning. But, stretching space is the same as acceleration because the line-of-site distance that photons travel increases.

At one time the consensus of so called informed / ruling people said the Earth was flat. Sail to far out and you’d fall off.

Sure, but we have computer models now... what could possibly go wrong?

 

[Hedges]

But how was "accelerating" determined?

I think you said, "Images were taken", later "measured again". Did they measure displacement which indicates movement? Did they do it a 3rd time and the new movement indicated higher velocity?

I thought the movement reported was away from us, not across our path (after all, we're the center of the universe?)

What I usually hear is Doppler effect, red shift, blue shift, see! the further galaxies are moving faster! That means they are accelerating! When the nearby galaxies get that far away, they will be moving that fast too!

 

[Bob B]

Getting off topic, but the one thing I never understood was the speed of light.

If an stationary object is approached by another object going 1/2 the speed of light with a light shining out in front of it ..... That light is still moving away from that object at the speed of light ...... the light that is received by the stationary object is also at the speed of light relative to it.
If I ponder that too long I have a mental spin out and have to go to therapy for a while ...LOL
I guess it all has to do with time and how it also changes for an object in motion ..... but, aren't we all in motion at a pretty high rate of speed already as the earth careens through space and spins.

 

[Bob B]

But how was "accelerating" determined?

I think you said, "Images were taken", later "measured again". Did they measure displacement which indicates movement? Did they do it a 3rd time and the new movement indicated higher velocity?

I thought the movement reported was away from us, not across our path (after all, we're the center of the universe?)

What I usually hear is Doppler effect, red shift, blue shift, see! the further galaxies are moving faster! That means they are accelerating! When the nearby galaxies get that far away, they will be moving that fast too!

I saw Steve Hawking explain it in a video series .... but I forgot ...LOL

 

[Woody]

But how was "accelerating" determined?

I think you said, "Images were taken", later "measured again". Did they measure displacement which indicates movement? Did they do it a 3rd time and the new movement indicated higher velocity?

I thought the movement reported was away from us, not across our path (after all, we're the center of the universe?)

What I usually hear is Doppler effect, red shift, blue shift, see! the further galaxies are moving faster! That means they are accelerating! When the nearby galaxies get that far away, they will be moving that fast too!

Not my area of training but I can Google. Maybe this will help.

How do astronomers know the universe is expanding?

Studying the wavelengths of light emitted by stars to see how far away they are and how fast they move

www.science.org.au

 

[Hedges]

"Studying the wavelengths of light emitted by stars to see how far away they are and how fast they move"

Yup, Doppler shift. Based on an assumption of wavelength at source, it indicates relative velocity relative to observer.
But unless you take two measurements at different times and see a different wavelength, you don't have indication speed has changed.
(be careful not to be confused by Earth's orbit or Milky Way's rotation.

The people who say it shows that expansion of the universe is accelerating haven't addressed that, nothing more than what's in that link plus, "Therefore, when the nearer star gets as far away as the farther star it will be traveling as fast."

 

[svetz]

But how was "accelerating" determined?

The "original" data from way back was that they saw the red-shifting of far-away galaxies was more severe and concluded galaxies farther away were drifting apart faster than closer galaxies, hence the universe was expanding.

But everyone "assumed" the rate had to be nearly constant with gravity slowing it down. The Hubble space telescope allowed astronomers to see more galaxies that were even farther away. The technique used was doppler shift, marker events, and math ... explained better here:

I thought the movement reported was away from us, not across our path (after all, we're the center of the universe?)

In a way, we are the center of the universe, but only because we can only observe the information that light brings to us.

 

[Hedges]

Thanks, new argument there I haven't heard before.

Regarding a plot of supernova velocity vs. distance (as determined by intensity and red shift)
"A straight line means it's expanding at a constant rate. A curve means it is speeding up or slowing down."

One possible flaw in that:

When I plot data, getting a point-slope, I find that whether it is straight or curved sometimes depends on zero-offset.
For the expanding universe topic, whether the observer (Earth) is at the center of the universe, the origin of the "Big Bang" or not, determines whether there is a zero-offset. I haven't seen or crunched the numbers, so I don't know how that affects the "acceleration" that has been calculated. Should be able to correct for it by looking at supernovae to the left and to the right, one on either side of the origin of Big Bang.

The other more basic flaw that I've always observed:
Different speed at different distance doesn't give acceleration (unless of same object.) Acceleration is one explanation (drop a bowling ball off the Empire State Building and measure its speed repeatedly with a radar gun.) Different initial velocity is another (fire a BB gun, a 9mm, and a 50-cal straight up. After a second measure their speed and position.)

An Astrophysicist was taking a walk in the countryside with his son. They came upon a group of animals watching a foot race. A few feet from the starting line, a tortoise was plodding forward. Half way across the field, a hare was sprinting quite fast. At the far edge of the field a cheetah was traveling at a dead run. After observing their speed and distance, the Astrophysicist said, "Son, the animals are accelerating! You see that tortoise? When it gets as far away as the hare is now, it will be sprinting as fast as the hare!"

If all matter (which coalesced into stars, began rotating about each other as galaxies, sometimes exploded as supernovae) left the big bang at the same instant but with varying velocity, then without acceleration their distance would be proportional to velocity, a straight line. Acceleration or deceleration would bend the curve one way or another, but difference in initial velocity would explain how they were spread out (and even if accelerating, wouldn't reach velocity of the further/faster objects for a given distance.) An alternative to acceleration/deceleration would be something to do with bending space or time due to extreme velocities or other conditions. I survived physics with straight A's, which doesn't mean I understood that part.

From my recollection of how velocity affects time, we see a fast-moving star taking a long time to get somewhere. To the fast moving star, time moves more slowly; when it gets to the same somewhere, it thinks less time has passed; at high velocity the distance seemed to be shorter. If it was traveling at speed of light it would think distance was zero. Different perception of time would alter wavelength seen by outside observers. I'm curious whether that correction has been applied to the Doppler shift calculation.

Of course accelerating a particle (or galaxy) to a fraction the speed of light takes an ever increasing amount of energy, shooting up to infinity to actually reach speed of light. The extra energy shows up as increase in mass (or so the math and theory says, confirmed by measurements. I don't claim to understand it.) That would alter how its velocity is affected by gravity or dark energy and therefore alters the curve, but I don't think it changes whether graph is straight line (no velocity change after traveling a distance) or which side of straight line the curve is on.

An alternate concept for Origin of Universe would be a continuous stream of matter. The rocket engine burned successfully, didn't explode on the launch pad. In this case, velocity of gasses probably has varied over time; if there was continuously both high and low velocity coming from it we would probably see late-starting galaxies with high speed overtaking and passing others. Not that we have the lifetime to observe the overtaking, but we would see a variety of velocities at any given distance. Continuous stream could go along with circular universe, where distance infinity is back at the center.

 

[svetz]

It would sure help if we knew what space was.

 

[time2roll]

I will just take their word for it.

 

[daviddakers]

Here's the 'latest'...

'There may not be a conflict after all' in expanding universe debate​

'There may not be a conflict after all' in expanding universe debate

Our universe is expanding, but our two main ways to measure how fast this expansion is happening have resulted in different answers. For the past decade, astrophysicists have been gradually dividing into two camps: one that believes that the difference is significant, and another that thinks it...

phys.org

 

[svetz]

Getting off topic, but the one thing I never understood was the speed of light.

Why no one has measured the speed of light.

But if you really want your mind blown...

 

[Samsonite801]

It would sure help if we knew what space was.

Have you ever watched any of Nassim Haramein's lectures?

 

[MurphyGuy]

Every point in the universe was at one point, the center of the universe.

The acceleration question actually has two parts.. One I understand, the other I'm still working on.

Type 1a SuperNova are standard candles.. this is because 1a SN are caused by binary systems where a white dwarf sucks hydrogen from a nearby companion star and explodes when it reaches critical mass, which is nearly the same for all white dwarfs..

There is new space being created between galaxies, and that new space is created at a constant rate. This new space isn't the result of the galaxies moving apart from each other, it is the cause of the galaxies moving away from each other.

This new space is being created at a rate of about 45 something miles per second per 3.3 million light years of distance. ( had to look that one up)..

Funny coincidence, with measurement error, the answer to the universe might really be 42 ! LOL

Because new space is being created at that rate, as it is created, the distance between objects increases, which means more new space is available to create more new space, hence, the acceleration is speeding up. This is a bit like interest on your bank account.. as your account accrues interest, there is more money in the account which accrues more interest.. the end result is that your money grows faster and faster.

When they say "the universe is expanding", people think the motion of the galaxies are moving them further apart from each other, but the strange reality is that the galaxies are not actually moving with any significant speed, the space between them is increasing because new space is being created between them.

Imagine a large rubber sheet.. using a crayon to draw galaxies randomly spaced on the sheet, you get a diagram of the universe. Now grab the sheet from the edges and stretch it out.. Make the 10ft diameter rubber stretch to 20 feet diameter. All the galaxies you drew on it are now further apart, but the drawings didn't actually move..
Overly simplistic to a point of almost being faulty, but the concept is sort of the same.. The galaxies are not racing outward, new space is being created between them.

I would surmise that another way to measure this expansion would be to measure the hydrogen between galaxies. Space isn't empty, its filled with stray atoms like hydrogen and helium, and that density is pretty uniform. Measuring the intergalactic density would/should tell us how much new space is being created as well as the distribution of that space. As new space is created, the density of that space should decrease.
Of course, this assumes that when new space is created, it is devoid of the normal stray hydrogen and other boson matter.

On a personal note: My totally unqualified opinion is that we are going to discover that both dark energy (expansion of the universe) and dark matter (unexplained gravity), are both going to be reconciled at the same time when we discover that we didn't account for some space-time effect.. I predict we will discover our measurements are skewed because of a subtle effect that the fabric of space has on the perceived speed of light.
For example, the wavelength of light might be stretched by the effect mass has on the space-time it distorts. Mass distorts space and time, and since frequency is a measure of time, the Doppler frequency we measure may be skewed in a way we have failed to predict.

We have invested billions upon billions of dollars into searching for dark matter, and to date, we have exactly zero. We have used super computers to run hypothesis, and one guess after another, and we come up with nothing.
We can not see it, we can not detect it directly, and yet is supposedly makes up the vast majority of all gravity and mass.. and the explanations make no sense at all.. They basically boil down to "its heavy but it doesn't clump together".. which triggers my BS detector.

 

[svetz]

Have you ever watched any of Nassim Haramein's lectures?

No... any suggested links?

 

[Hedges]

We have invested billions upon billions of dollars into searching for dark matter ...

And that is at the crux of my suspicions, related to why no-one questions the "fact" that expansion is accelerating.

At least now I have an understanding of what suggests that it is: Position is not linear with velocity, suggesting a velocity change has occurred.

 

[Hedges]

Here's the 'latest'...

'There may not be a conflict after all' in expanding universe debate​

'There may not be a conflict after all' in expanding universe debate

Our universe is expanding, but our two main ways to measure how fast this expansion is happening have resulted in different answers. For the past decade, astrophysicists have been gradually dividing into two camps: one that believes that the difference is significant, and another that thinks it...

phys.org

It took them a while, but looks like the astrophysicists are coming around to my way of thinking

"I really wanted to look carefully at both the Cepheids and red giants. I know their strengths and weaknesses well," said Freedman. "I have come to the conclusion that that we do not require fundamental new physics to explain the differences in the local and distant expansion rates. The new red giant data show that they are consistent."

The value of the Hubble constant Freedman's team gets from the red giants is 69.8 km/s/Mpc—virtually the same as the value derived from the cosmic microwave background experiment. "No new physics is required," said Freedman.

"Some scientists who have been rooting for a fundamental mismatch might be disappointed."

 

[svetz]

And that is at the crux of my suspicions, related to why no-one questions the "fact" that expansion is accelerating.

Theories not facts. Practically everything is just a theory.

I'm more concerned about all the used-to-be young Millenials that spent the last 20 years researching it and may just now be realizing they completely wasted all that brainpower and all the hard work may now be akin to TP.

Well, there's always the other stupid theory (dark matter).

If you're not familiar with this one it's about orbital speeds. In our solar system all the planets move at different speeds, they have to travel just fast enough to fall over the sun (when you hear people say there's no gravity in space just laugh at them, they're clueless). So top down it looks like this with Mercury whizzing around and the outer planets being pokey.

Galaxies are still bound by gravity... but all the solar systems are moving as if stuck on a rotating platter ... rather than the inner rotating faster than the outer (sort of like the gif below). Since we don't know why it's was coined dark matter because something we can't see/detect is affecting the masses.

At least that's my popular science understanding of it. ;-)