Celestia Forums

Have you ever think of it? The speed of light is (what i see in wikipedia ) 299,792,458 metres per second. So, maybe some of the stars or nebulas are actually gone now.. Example, the LMC is maybe 148.000 lightyears away, so the LMC we see from photos or our own eyes is what we supposed to see 148000 years ago if lightyears have infinite speed!
So the point is, we can't really create a very accurate position of stars or something in celestia.. It only resembles the stars we see 'now'... or the 'past'?

That's true, and easy to forget when going around the Universe in Celestia.

Verz Veraldi wrote:...
Example, the LMC is maybe 148.000 lightyears away, so the LMC we see from photos or our own eyes is what we supposed to see 148000 years ago if lightyears have infinite speed!

Therefore all the deep space objects are at same distance?

yeah, but no, fenerit.. every dso have a different distance. what i mean 'LMC' is the large magellanic cloud, an irregular galaxy near us. other dso like orion nebula or something is closer..

Verz Veraldi wrote:Have you ever think of it? The speed of light is (what i see in wikipedia ) 299,792,458 metres per second. So, maybe some of the stars or nebulas are actually gone now.. Example, the LMC is maybe 148.000 lightyears away, so the LMC we see from photos or our own eyes is what we supposed to see 148000 years ago if lightyears have infinite speed!
So the point is, we can't really create a very accurate position of stars or something in celestia.. It only resembles the stars we see 'now'... or the 'past'?

Of course we are looking far back in time in astrophysics and cosmology, since the speed of light is finite (rather than being infinite). A most extreme case concerns the famous cosmic microwave background radiation (CMB) (WMAP site: http://map.gsfc.nasa.gov/), that allows us to directly probe the physical conditions at this epoch, only 380,000 years after the Big Bang.
From that amazingly successful WMAP experiment we also know the most precise value of the age of the Universe = 13.73 billion years to within 1% !

Fridger

t00fri wrote:

Of course we are looking far back in time in astrophysics and cosmology, since the speed of light is finite (rather than being infinite). A most extreme case concerns the famous cosmic microwave background radiation (CMB) (WMAP site: http://map.gsfc.nasa.gov/), that allows us to directly probe the physical conditions at this epoch, only 380,000 years after the Big Bang.
From that amazingly successful WMAP experiment we also know the most precise value of the age of the Universe = 13.73 billion years to within 1% !

Fridger

but where is the cosmic microwave background radiation located? Everywhere? Space expands everywhere, resulting of the unknown matter(s), but is it possible to draw certain conclusions where the big bang is located?
Because we "know" now, the cosmic microwave background radiation is a quasi witness of the - 380 000 years before exploding - big bang. this is implying for me, that we are able to know where the big bang was "started"? Or, is also the location of the big bang "everywhere"...? and still continues (expanding space)... ?
The cosmic microwave background radiation is even in my TV ( but it's not the badest broadcasting my TV is showing ).
Michael

Verz Veraldi wrote:yeah, but no, fenerit.. every dso have a different distance. what i mean 'LMC' is the large magellanic cloud, an irregular galaxy near us. other dso like orion nebula or something is closer..

Yep! Mine was just an appoint against the use of the infinite and its paradoxes in measurement. If there is a supposed "infinite" distance amongst us and LMC, there will be also an "infinite" distance among the LMC and, to say, M 101; as well as amongst us and M 101, just to exploits roughly the mathematical issues concerning the power of the continuum. Nonetheless, you should have been of the opinion that in reply to my enquire about the same distance for the deep space objects, the Big Bang was just such distance, in which all the objects are together; but it should be still at "infinite" and not, how Fridger point out, at "13.73 billion years to within 1%!".
That the speed of light were infinite was thought in the past, accordingly with the famous antropocentric vision that no delays there are in sight stars after quick closing and opening of the eyes.

MiR wrote:

t00fri wrote:

Of course we are looking far back in time in astrophysics and cosmology, since the speed of light is finite (rather than being infinite). A most extreme case concerns the famous cosmic microwave background radiation (CMB) (WMAP site: http://map.gsfc.nasa.gov/), that allows us to directly probe the physical conditions at this epoch, only 380,000 years after the Big Bang.
From that amazingly successful WMAP experiment we also know the most precise value of the age of the Universe = 13.73 billion years to within 1% !

Fridger

but where is the cosmic microwave background radiation located? Everywhere? Space expands everywhere, resulting of the unknown matter(s), but is it possible to draw certain conclusions where the big bang is located?
Because we "know" now, the cosmic microwave background radiation is a quasi witness of the - 380 000 years before exploding - big bang. this is implying for me, that we are able to know where the big bang was "started"?

NOTE: The CMB radiation originates from 380000 years AFTER the BB not before (as you wrote)!

The CMB photons are associated with the so-called surface of last scattering (photon-decoupling). For understanding today's observations, it's crucial to recall that the Universe was very small only 380000 years after the BB (about 1 degree^2 in today's sky!)! Using those CMB photons we cannot get closer towards the BB, since in this regime the Universe is entirely opaque ("dark") as concerns photons("light")! From WMAP we know the time of the BB pretty well as I wrote above: (13.73 +- 1%) billion years ago, which follows directly from measuring the inverse Hubble constant 1/H0, as WMAP did.

Here is the familiar summary illustration from the WMAP site, with time as horizontal axis and the universe being depicted as (expanding) 2D circular domain at each time:



++++++++++++++++++
But NOTE: to probe the Universe much closer to the BB, we could use in principle the cosmic relic radiation associated with neutrinos. The latter are known to decouple much earlier, at a temperature of ~ 1MeV corresponding to only ~ 1 second after the BB! The relic radiation from neutrinos is of course much harder to detect than the CMB photons, but it's not impossible under certain favorable circumstances. From the Standard model we know the neutrino density precisely in terms of the one for photons: <n_nu> = <n_nubar> = 3 / 22 <n_photon> = 56 /cm^3.

Thus cosmic relic neutrinos would have a real chance of probing the cosmic Inflation period that started right after the BB, leading to a temporary exponential expansion of the universe.
++++++++++++++++++

Or, is also the location of the big bang "everywhere"...? and still continues (expanding space)... ?

Naively speaking: yes. A deeper understanding requires knowledge of GR (general relativity).

Fridger

Fridger,

Thanks for the comprehensive reply.

MiR wrote:Because we "know" now, the cosmic microwave background radiation is a quasi witness of the - 380 000 years before exploding - big bang.

t00fri wrote:
NOTE: The CMB radiation originates from 380000 years AFTER the BB not before (as you wrote)!

This annoying me; I wrote this in a hurry. I apologize for my "german" english. I promise: I'll keep on learning. (Of course, the cosmic microwave background radiation appears 380 000 years after the big bang. If I know what's happened before probably I would be the first non-scientist who would get the Nobel price in physics )

Here is the familiar summary illustration from the WMAP site, with time as horizontal axis and the universe being depicted as (expanding) 2D circular domain at each time...

I know about the WMAP site (and the image above). But this image is also showing only a two (or three-) dimensional parable of the universe (and shows the big bang as an explosion at one point...)

General relativity theory is not entirely unfamiliar for me. But it might be pretty difficult to explain a non-mathematician (like me) cosmo-mathematical knowledge.

There are many more questions i would like to ask but i fear it's already out of topic...
so, thank you very much again for the detailed explanation. And for your Celestia activities of course!

Michael

Michael,

perhaps a little addendum might be useful: The surface of last scattering, where the CMB photons are emerging, arises as follows:

The closer one gets to the BigBang(BB), the higher gets the temperature of the early Universe. Correspondingly, there will be a surface in 3D space that defines the distance (time) from the BB, below which all matter is ionized in form of electrons, positrons and charged nuclei (p,n) due to the tremendous heat. In contrast, below a critical temperature, the various ions recombine into neutral atoms (hydrogen!), and photons cease to be scattered from the resulting neutral matter! This is unlike the ionized phase, where scattering of photons is frequent due to the free electric charges! Therefore the latter regime becomes totally opaque (the light never arrives in our eyes, due to the intense scattering). Once the temperature has become low enough that the Universe is mainly filled with neutral hydrogen, the scattering of photons ceases and thus the Universe becomes transparent for photons (i.e. we can see through!). That rather sudden transition defines the surface of last scattering and the released photons along that surface make up the CMB radiation that we can observe almost undisturbed..


Fridger

So why are quasars always so far out? Do they not exist anymore and we are just seeing an after image of them?

Reiko wrote:So why are quasars always so far out? Do they not exist anymore and we are just seeing an after image of them?

In cosmology you can qualitatively associate distance with time. So the very far out objects represent also very young objects (counted from the BB). As you can see in the above illustration, no stars or galaxies exist yet right beyond the CMB surface of last scattering. It will take quite a while until these will have formed. So galaxies and stars are less far out from us in distance. The quasars represent even earlier stages of development, hence they are farther out (seen from the observer). Next come galaxies that don't have spiral structure yet. They are mostly elliptical blobs.

When the images of the far-out objects arrive with us, we don't know whether they still exist at the arrival time of the image from their "youth".

Fridger

This discussion suggests a question. If the radiation in any form (ie. light or energy in any form) which travels a the speed of light or a fraction of it is just reaching us now, it suggests that the universe is expanding at a rate that is higher than the speed of light. Now, we know that this is not possible.

Or is this radiatioin arriving at us (travelling observation point) after having bounced around the confines of the universe many times?

I am definitely not a scientist but I am enjoying this discussion for learning purpose and I am glad to see all of you participating in it; from the neophyte like myself to the knowledgeable like t00fri and others.

NorthOfPolaris wrote: it suggests that the universe is expanding at a rate that is higher than the speed of light. Now, we know that this is not possible.

You're measuring the velocity of these epic-distant galaxies relative to Earth. Relative to their location, they are stationary, and it is Earth that is moving away faster than light.

You can't move faster than light relative to your local spacetime. What happens at the other end of the Universe is irrelevant, so long as they're not moving faster than light relative to their local spacetimes.

Consider the expanding balloon analogy. Each dot on the balloon has an equal right to think it's stationary, yet all the other dots are moving away at speeds that increase, the further from the perspective dot.

(wow, this thread moves faster than light... and i have so much to work...)

t00fri wrote:Michael,

perhaps a little addendum might be useful: The surface of last scattering, where the CMB photons are emerging, arises as follows:

The closer one gets to the BigBang(BB), the higher gets the temperature of the early Universe. Correspondingly, there will be a surface in 3D space that defines the distance (time) from the BB, below which all matter is ionized in form of electrons, positrons and charged nuclei (p,n) due to the tremendous heat. In contrast, below a critical temperature, the various ions recombine into neutral atoms (hydrogen!), and photons cease to be scattered from the resulting neutral matter! This is unlike the ionized phase, where scattering of photons is frequent due to the free electric charges! Therefore the latter regime becomes totally opaque (the light never arrives in our eyes, due to the intense scattering). Once the temperature has become low enough that the Universe is mainly filled with neutral hydrogen, the scattering of photons ceases and thus the Universe becomes transparent for photons (i.e. we can see through!). That rather sudden transition defines the surface of last scattering and the released photons along that surface make up the CMB radiation that we can observe almost undisturbed..


Fridger

Fridger,

yes, this sounds logical. And it's in passing a very understandable explanation for the transition between the invisible and the visible universe! (Thanks)

...The closer one gets to the BigBang(BB), the higher gets the temperature of the early Universe.

But what kind of condition would we find before these high temperatures near the BigBang?
Temperature means energy. And energy should be the preliminary stage of matter (quarks, leptons -> protons, etc -> atoms -> ...galaxies).
All forces are already integrated in the singularity as one force. Consequently all the energy (and hence the future mass) as well.

To here we are d'accord i think.
But what kind of force creates the energy?

And, where is "time" in this draft? To my mind "time" is more than a measurement for space relations. "Time" isn't a continuous "line" (Of course you know this). Near black holes there are "plenty" of time (in the meaning of Planck time, 10-43 seconds). Time nearly standstill. In free space there are not much (Planck-) time units and time runs...

In most of the articles i've read about the BigBang "Time" is - more or less - neglected. Only it is said "BigBang is the beginning of time (energy and matter)". But not further scrutinized.

I may repeat: All forces are already integrated in our little singularity as one force. And all the energy and mass. And maybe our singularity had already included - besides energy and mass - all the tiny little time-pieces as well?

Our material universe originated from energy. (mass - energy equivalence) And that's all? And energy? I'd like to say: Energy originated from "time". It must be "time". Because "time" is the first and the main condition for everything. Without time nothing can exists.

Too late now; i'm getting tired; what i've wrote sounds like the quintessence of my thinking. But it should be more a question...

For me "time" is the biggest puzzle and time is the most unexplored quantity in science. Maybe we need a four-dimensional cognitivity at first. To understand "time".

Michael

MiR wrote:
Our material universe originated from energy. (mass - energy equivalence) And that's all? And energy? I'd like to say: Energy originated from "time". It must be "time". Because "time" is the first and the main condition for everything. Without time nothing can exists.

Under the conditions of the principle of indetermination, the physical time-relations are ambiguous. Virtual particles have an existence not directly "conform" to the standard, "common" time; just their effects.

MiR wrote:Too late now; i'm getting tired; what i've wrote sounds like the quintessence of my thinking. But it should be more a question...

Better than count sheeps...

MiR wrote:For me "time" is the biggest puzzle and time is the most unexplored quantity in science. Maybe we need a four-dimensional cognitivity at first. To understand "time".

Space, the last frontier...

Hi Massimo,

Under the conditions of the principle of indetermination, the physical time-relations are ambiguous. Virtual particles have an existence not directly "conform" to the standard, "common" time; just their effects.

...but also the virtual particles needs "time" to exist. Albeit a very short time... Virtual particles originates from the empty space. But the empty space is anything but empty... high energetic instead.

Michael

MiR wrote:Hi Massimo,

Under the conditions of the principle of indetermination, the physical time-relations are ambiguous. Virtual particles have an existence not directly "conform" to the standard, "common" time; just their effects.

...but also the virtual particles needs "time" to exist. Albeit a very short time... Virtual particles originates from the empty space. But the empty space is anything but empty... high energetic instead.

Michael

IMHO, you ascribe to the "time" a vast meaning; virtual particles have either an energy (quantity of motion) or the position, and such relations cannot measured (undetermined) whether taken as a whole, thus, while you do know its energy, its position is undetermined respect to the "time" because you cannot say that the particle is "here and now" (its virtuality as event). And when you know that the particle is "here and now" you cannot know "what" is here and now (its virtuality as object). Paradoxally, the sentence that "virtual particles needs "time" to exist", could be rephrased as: "virtual particles needs "apple" to exist".

Massimo,

please take a look:

http://en.wikipedia.org/wiki/Virtual_particle
-> "In physics, a virtual particle is a particle that exists for a limited time and space..."
or
http://en.wikipedia.org/wiki/Uncertainty_principle
-> "time" is very tiny but cannot be zero.

Michael

Sorry guys,

the last 5 posts about time, energy and virtual particles are largely incorrect or "half-digested" at best. Unfortunately, a proper exposition would require more time than I currently have. Wikipedia is not a good reference in these matters (where the actual qualifications of the writer about such subtle matters remains entirely unknown...).

Only so much:
while in non-relativistic physics there is only one time for all (inertial) frames, this is becoming different in Relativity. Besides the 3 space coordinates, also time is transformed between different coordinate frames in special and general Relativity. So --depending on the considered frame-- there are many 'times' in principle, and thus speaking about "time" requires plenty of care to start!

Moreover, in Relativity, the 3 space coordinates and time are treated absolutely equal (forming a 4-component vector). Only such a 'democratic' treatment of space and time allows to exhibit the most elegant feature of covariance in the underlying equations. This basic concept begins with the covariant form of the famous Maxwell equations of Electro-Magnetism and ends with general covariance in Relativity.

Fridger