JEROME - Life and Linear Time

[aggle-rithm]

The Big Bang is assuming an origin.

You may have already addressed this, but I am curious:

If you spin the clock backwards to the point in time when the present expansion began, what do YOU think happened before that time?

If the observable universe was not in one point in space-time in the distant past, then what happened? Was everything moving in some other direction, and then suddenly decided to mimic an outward expansion?

 

[aggle-rithm]

A gnome is needed to explain the accelerated expansion. Should this not call into question our perceptions of the data?

Perhaps, but the Big Bang theory was fully formulated before the accelerating expansion was observed. In other words, a theory to explain the acceleration is not strictly necessary to explain the Big Bang. It may help refine the theory if we understood it better, but accelerating expansion in no way contradicts it.

If you have an alternate theory, then to be taken seriously it needs to explain why the universe appears as it does today. Just saying that our observations COULD be distortions of reality is simply introducing an unnecessary ad-hoc explanation.

 

[Wangler]

So we've measured the distance and velocity of lots of stars, and we notice that they are related linearly - the further away they are, the faster they are moving - and they're always moving away from us, never towards (not counting very nearby stars like those in our own galaxy). Symbolically, v = H*d, where v is velocity, d is distance, and H is a constant called the Hubble constant.

Sol,

I think that you meant to say: "So we've measureed the distance and velocity of lots of galaxies...."

Also, even though you have Doppler shift as an example, isn't redshift you describe more related to the expansion of the universe itself, and not a pure Doppler shift?

 

[aggle-rithm]

So we've measured the distance and velocity of lots of stars, and we notice that they are related linearly - the further away they are, the faster they are moving - and they're always moving away from us, never towards (not counting very nearby stars like those in our own galaxy).

And nearby galaxies, like Andromeda.

 

[aggle-rithm]

Also, even though you have Doppler shift as an example, isn't redshift you describe more related to the expansion of the universe itself, and not a pure Doppler shift?

Hmmm...

Is there really a meaningful difference between light that is red-shifted by the relative motion of observer and observed, and light that is red-shifted by expanding space-time? From the light's point of view, wouldn't it be the same?

 

[aggle-rithm]

Please explain how we have come to the conclusion that light can be measured for age.

It's not necessary to analyze it that closely.

If the universe has always existed, then the light from all the stars in the universe have had an eternity to make to to Earth. We would be able to see every star in the universe with the naked eye, such that the night sky would be filled with light!

That's not what I observe, anyway.

 

[sol invictus]

Sol,

I think that you meant to say: "So we've measureed the distance and velocity of lots of galaxies...."

Yes, it's generally impossible to resolve individual stars in distant galaxies. I was just trying to explain the basics of this in the simplest way possible.

Also, even though you have Doppler shift as an example, isn't redshift you describe more related to the expansion of the universe itself, and not a pure Doppler shift?

What aggle-rithm said. You can always think of cosmological redshift as arising from the relative motion of the two objects. It's not always the most convenient way to do things, but in this case I think it's the most intuitive.

 

[Wangler]

Is there really a meaningful difference between light that is red-shifted by the relative motion of observer and observed, and light that is red-shifted by expanding space-time? From the light's point of view, wouldn't it be the same?

To be pedantic about it, see Wikipedia: http://en.wikipedia.org/wiki/Redshift

With a quote:

As a result, photons propagating through the expanding space are stretched, creating the cosmological redshift. This differs from the Doppler effect redshifts described above because the velocity boost (i.e. the Lorentz transformation) between the source and observer is not due to classical momentum and energy transfer, but instead the photons increase in wavelength and redshift as the space through which they are traveling expands.

 

[sol invictus]

To be pedantic about it, see Wikipedia: http://en.wikipedia.org/wiki/Redshift

With a quote:

That quote doesn't make sense. Doppler shifts are Doppler shifts - it doesn't make any difference where the velocity that caused them came from.

One valid technique for calculating cosmo redshift is to compute the geodesic of the source, and then compute its velocity with respect to the observer receiving the light (us). The redshift is then given by the standard relativistic Doppler formula. It's true that the geodesics are different from what they would be in flat space, but so what?

Expansion of space is not a gauge-invariant concept, because it refers to a particular choice of space and time coordinates. The redshift, on the other hand, is a physical quantity and therefore gauge invariant. So it's really the redshifts that are fundamental, not the expansion, and it's perfectly valid to regard them as due to relative velocities.

 

[Jimbo07]

If the universe has always existed, then the light from all the stars in the universe have had an eternity to make to to Earth. We would be able to see every star in the universe with the naked eye, such that the night sky would be filled with light!

How perfectly 19th C. of you. I don't understand this, however. Even if the universe is infinite in age, the stars are not evenly distributed. I'd expect to see bright and dark patches...

 

[chulbert]

If the universe has always existed, then the light from all the stars in the universe have had an eternity to make to to Earth. We would be able to see every star in the universe with the naked eye, such that the night sky would be filled with light!

While such a universe might be eternal, the individual stars within it are not. All the stars in such a universe would have long since burned out and left the night sky dark unless there was a process that produced new stars. If so, it is reasonable to assume that at any given time there would exist some new stars far enough away that their light has not yet reached Earth.

Whether or not we would see more stars in such a universe, I can't say - it depends on the birth and death rates.

(No, I don't believe we live in such a universe.)

 

[Jimbo07]

Even if the universe is infinite in age, the stars are not evenly distributed. I'd expect to see bright and dark patches...

While such a universe might be eternal, the individual stars within it are not.

Two minutes apart, but picking up on the same theme... weird... can we split the million?

 

[chulbert]

Two minutes apart, but picking up on the same theme... weird... can we split the million?

Deal.

 

[Jimbo07]

Deal.

Okay, then. I promise to give you exactly half of everything I win from this event!

...

We're trying to trip aggle-rithm up, but in general, I agree that for the lay person, much can be learned through straightforward observation. We just have to be very careful with induction... science is whacky that way!

 

[mhaze]

[sol invincus]
Now imagine a bomb exploding. Some particles fly away from the bomb quickly, some more slowly. If you survive the blast and are sitting at the center (where the bomb was) some time later, you'll observe stuff all around you, all moving away, and the further away something is, the faster it's moving (with a speed proportional to distance).[/quote]

Huh? You may be thinking of gas expansion in a vacuum, but explosions occur at a pretty set rate - say 50,000 fps for a high explosive, 7-11,000 for something like high density hydrogen peroxide. In the center of the blast and going outward is gas expansion, yes, and aggregate or particles have only the velocity imparted by the energetic gas. Those particles, their energy clearly declines with distance due to atmospheric drag. As for the gas, it expands until it's pressure is less than atmospheric, at that point chaotic whirls occur in which the remainder of the kinetic energy is used up. Conservation of energy is required throughout the blast and the expansion of the blast.

So 'speed proportional to distance' - Nope, except in the very initial stage when outer (spherical layers) of gas and particles were being accelerated by inner layers which were of higher energy.

In another thread, I asked JEROME DA GNOME to clarify ....

Jerome contents that the universe has always existed - it is eternal both into the past and into the future. This idea contradicts the most accurate mathematical description of the universe we have. If Einstein was correct (and as far as we can tell, he was), then the universe cannot be eternal.

I open the floor to discussion.

This is really a bit silly. If I recall correctly, the words Stephen Hawking used to discuss "time" outside of the universe, eg, at the moment before the beginning of the big bang expansion, was as follows:

"Time is undefined".

Correct from the relativity work.

Now, has the universe always existed? Could there have been an endless succession of big bangs, each with a "time" attribute? If so, is there a mechanistic and sequential series of these these discrete instances of "time"? Obviously not, because there could be no linkage where time did not exist.

Hawking's point carried somewhat further what in common and religious lore was described historically as "infinite" time. Time was not equal or similar in extent to the mathematics symbol for infinite...

 

[sol invictus]

While such a universe might be eternal, the individual stars within it are not. All the stars in such a universe would have long since burned out and left the night sky dark unless there was a process that produced new stars. If so, it is reasonable to assume that at any given time there would exist some new stars far enough away that their light has not yet reached Earth.

I don't understand your idea. You're proposing that the universe just sat there for an infinite amount of time, and then - after an infinite amount of time - lots of stars were born, burned out - and then it sat (or will sit) for another eternity? Doesn't sound very reasonable... what triggered those stars to ignite then? Why didn't they ignite earlier, when they had an eternity?

Huh? You may be thinking of gas expansion in a vacuum,

Yes, I was talking about a vacuum. I specified that the only force acting is gravity.

So 'speed proportional to distance' - Nope, except in the very initial stage when outer (spherical layers) of gas and particles were being accelerated by inner layers which were of higher energy.

Speed is proportional to distance in an explosion when there are no forces acting. The universe does not expand into an atmosphere - there is nothing outside it to push back on it.

 

[arthwollipot]

Another talking point:

JEROME, do you believe that the universe is infinite in spacial extent?

 

[JEROME DA GNOME]

Another talking point:

JEROME, do you believe that the universe is infinite in spacial extent?

The evidence suggests nothing for this question. I do know that as far out we have looked we find more and as far in as we have looked we find more. Barriers have not been evidenced at this point.

 

[arthwollipot]

The evidence suggests nothing for this question. I do know that as far out we have looked we find more and as far in as we have looked we find more. Barriers have not been evidenced at this point.

Do you think it's more likely that there's an edge to the universe, or that the universe is infinite? I understand that there's no evidence, but what's your opinion?

 

[JEROME DA GNOME]

Do you think it's more likely that there's an edge to the universe, or that the universe is infinite? I understand that there's no evidence, but what's your opinion?

My presumption based upon our current evidence? The universe is infinite both large and small.