space is expanding,,, wait what??

[tsmspace]

If space is expanding because SPACE is moving, not the objects in it,,,, then it is possible for the objects far away from us are moving away from us faster than light,,,,, but if this is because they are NOT moving ACROSS SPACE,,, then HOW do we perceive a red-shift from the expansion??? IF at all times the light is simply travelling across normal space at normal speed, and the objects in space are not moving ACROSS SPACE apart from each-other, then the light should simply cross MORE SPACE, not impact our telescopes as though we are moving away from the light,,, therefore this expansion,,,, how can it result in red-shift???

[RuffRuffmcgruff]

[tsmspace]

*mark as solved

 

[jones177]

Not according to my theory of everything.

 

Things are not moving away. We and everything else are shrinking or the distance between the nuclei and the electron cloud is getting smaller along with the particles that make them up.

 

Soooo if you look at it that way everything starts to make sense.

 

Or not.

 

[Sauron]

 

[Dash Lambda]

Think of it like a gas. You know how using a compressed air can for too long will make it get really cold? If space is expanding, then the photons traveling through it get stretched out and 'colder' over time.

 

A good example is the Cosmic Microwave Background (CMB), which is light from the moment the universe went from an opaque plasma to a transparent... Something. It was extremely hot and bright at the time, but over the course of billions of years the universe/space has expanded and it's cooled down to the point where it's below the visible spectrum.

 

25 minutes ago, jones177 said:

Things are not moving away. We and everything else are shrinking or the distance between the nuclei and the electron cloud is getting smaller along with the particles that make them up.

That's not really what we're observing. At large scales the expansion of space pushes things away, but at small scales, specifically at the local group and below, gravity and electromagnetism overpower it. At human scale they overpower it so much that it's completely undetectable.

[jones177]

1 minute ago, Dash Lambda said:

Think of it like a gas. You know how using a compressed air can for too long will make it get really cold? If space is expanding, then the photons traveling through it get stretched out and 'colder' over time.

 

A good example is the Cosmic Microwave Background (CMB), which is light from the moment the universe went from an opaque plasma to a transparent... Something. It was extremely hot and bright at the time, but over the course of billions of years the universe/space has expanded and it's cooled down to the point where it's below the visible spectrum.

 

That's not really what we're observing. At large scales the expansion of space pushes things away, but at small scales, specifically at the local group and below, gravity and electromagnetism overpower it. At human scale they overpower it so much that it's completely undetectable.

That was part of Fred Hoyle's "Steady State" universe theory. He was the first person to use "Big bang" to describe the expanding universe model.

I took astrophysics/cosmology in the 70s(no internet so there was not much else to do) and he wrote one of the textbooks I had to get. 

 

That is about all I remember of it.

[harryk]

6 hours ago, tsmspace said:

If space is expanding because SPACE is moving, not the objects in it,,,, then it is possible for the objects far away from us are moving away from us faster than light,,,,, but if this is because they are NOT moving ACROSS SPACE,,, then HOW do we perceive a red-shift from the expansion??? IF at all times the light is simply travelling across normal space at normal speed, and the objects in space are not moving ACROSS SPACE apart from each-other, then the light should simply cross MORE SPACE, not impact our telescopes as though we are moving away from the light,,, therefore this expansion,,,, how can it result in red-shift???

Space is not moving. Space is getting bigger. Everything in the universe is also expanding with space, however on small scales there are other forces like gravity and EM which pull things back together. To an outside observer nothing appears to get bigger, but everything appears to get further apart. Light is the exception. The only force that interacts with light is gravity, and weakly at that. So as the light waves are traveling through space, not only do they have to travel further to reach us, they are continually being stretched as the space they inhabit expands. 

 

 

[tsmspace]

But according to the same theory, light doesnt lose energy, and since the expansion only results in more space, not motion of objects through space, then the expansion shouldnt cause redshift. Only if the expansion resulted in motion across space should the light redshift as a result. 

[tsmspace]

7 hours ago, harryk said:

Space is not moving. Space is getting bigger. Everything in the universe is also expanding with space, however on small scales there are other forces like gravity and EM which pull things back together. To an outside observer nothing appears to get bigger, but everything appears to get further apart. Light is the exception. The only force that interacts with light is gravity, and weakly at that. So as the light waves are traveling through space, not only do they have to travel further to reach us, they are continually being stretched as the space they inhabit expands. 

 

 

No, i thought that the waves were NOT stretching, because they are not waves over space-time, but wave-particle dualities. An ocean wave can stretch, a photon wave does not. Instead the lower frequency of the redshift is due to the lower energy of impacting an object moving in the same direction,,, so like shooting at a car moving away. The frequency of light is correlated to the energy a photon has, more energy means a higher frequency. ....

 

Like, the photon is the wave, it doesnt stretch. (According to someone else, not me). 

[harryk]

3 hours ago, tsmspace said:

But according to the same theory, light doesnt lose energy, and since the expansion only results in more space, not motion of objects through space, then the expansion shouldnt cause redshift. Only if the expansion resulted in motion across space should the light redshift as a result. 

Aha! Photons do have a definite energy which is dependent on their wavelength. Redshift changes that wavelength and results in a blatant violation of the conservation of energy ...at least in classical Newtonian physics. 

 

This a big problem; and one that hasn't really been solved yet. If you google "redshift conservation of energy" you will find many different explanations. But the truth is general relativity does not require energy to be conserved. Einstein told us that space and time are coupled and are dynamic. In the equations that define general relativity (and how our universe works), if spacetime is constant then energy is conserved, but if spacetime is changing then the energy evolves in a specific manner in response the the changes in the space around them.

 

In the future, a unified theory of physics, often dubbed The Theory of Everything, may include a better definition of gravity or of general relativity which will better explain this apparent conflict. 

[harryk]

2 minutes ago, tsmspace said:

No, i thought that the waves were NOT stretching, because they are not waves over space-time, but wave-particle dualities. An ocean wave can stretch, a photon wave does not. <snip>

Wave-particle duality is another one of those weird physics realities. We think we have it figured out but it's on the fringe of explanation. In general, light acts as a particle, a photon, when it interacts with matter. Light acts as a wave when interacts with itself or with other fields. It's really way more complicated than that, but it's a good way to think about it. 

 

10 minutes ago, tsmspace said:

Instead the lower frequency of the redshift is due to the lower energy of impacting an object moving in the same direction,,, so like shooting at a car moving away. The frequency of light is correlated to the energy a photon has, more energy means a higher frequency. ....

It's important that we now differentiate redshift due to the expansion of space, and redshift due to the doppler effect. On the surface they look the same but are explained by entirely different physics. In the doppler effect redshift the light waves do have a lower energy as the object moves away from us.

[tsmspace]

I have been arguing about this one before, because I think it's possible that the light loses energy without needing expansion,,,, 

 

but I was pretty sure the light was dopplar shifting for us to percieve the distance, not stretching. others seemed to think so too. 

 

here's what they all basically said. There are two points of redshift for distant universe light. THe light shifts one time when it departs the star (which makes no sense to me, ESPECIALLY if the star is not moving for the expansion), and one shift when the light hits the telescope (which also makes no sense to me, if we aren't actually flying away from the photon). The specific reason that the light doesn't stretch, is because it's not a wave of particles bouncing off of eachother, it's just an energy level of a single particle. 

 

So the doppler redshift is understood with the analogy of a bullet fired from a moving car, hitting another moving car. therefore is understood the light departing the distant star, and hitting the telescope. 

 

light that interacts with other objects is basically must have been deflected. it is basically assumed that the light we see from that distance didn't hit anything first. it just flew uninterrupted until it hits the telescope. There are other important concepts, but ignoring all of the details like gravitational lensing, you can generalize by saying the photon never lost any energy along the way. the only two points that matter are departure and arrival.......

 

for the record the photons are flying through a huge space of ,,,,,,, other photons, so although we say photons don't affect other photons, I seriously can imagine the light losing energy along the way, and the universe is simply not expanding. The universe can still be imagined as endless, with endless objects. No beginning, no end,,, black holes don't swallow everything, they just soak stuff up a while then they too find a way to die. time just goes on forever with no beginning and no end. 

 

I mean who am I to say but if you told me that was right I would be like,,, makes more sense than that other malarky. 

[harryk]

6 hours ago, tsmspace said:

I have been arguing about this one before, because I think it's possible that the light loses energy without needing expansion,,,, 

 

but I was pretty sure the light was dopplar shifting for us to percieve the distance, not stretching. others seemed to think so too. 

If you want to gain a good understanding of light, I highly recommend Richard Feynman's book QED: The Strange Theory of Light and Matter, it is one of the best explanations of light ever written.

6 hours ago, tsmspace said:

So the doppler redshift is understood with the analogy of a bullet fired from a moving car, hitting another moving car. therefore is understood the light departing the distant star, and hitting the telescope. 

This analogy only works for doppler shift not for cosmological redshift. If you apply the doppler shift equation to distant galaxies you discover three things:

- these galaxies are moving at tremendous speeds close to the speed of light

- the more distant a galaxy is the faster it is moving

- every galaxy is moving away from Earth

 

We know that accelerating objects to high speeds takes a lot of energy, and reaching near light speed takes an unthinkable amount of energy. That begs the question of what could possibly have accelerated these massive galaxies to the speed of light? And why do they appear to be speeding up as they get farther away? And why is everything moving away from us? The simple answer is that the galaxies are not moving, but space itself is getting bigger thus everything in it more distant from each other. 

 

6 hours ago, tsmspace said:

for the record the photons are flying through a huge space of ,,,,,,, other photons, so although we say photons don't affect other photons, I seriously can imagine the light losing energy along the way, and the universe is simply not expanding. The universe can still be imagined as endless, with endless objects. No beginning, no end,,, black holes don't swallow everything, they just soak stuff up a while then they too find a way to die. time just goes on forever with no beginning and no end. 

If photons were losing energy to something else then our entire understanding of light and electrodynamics is wrong. Additionally this would be something we should easily be able to detect and measure in a lab setting. 

 

We have other sources besides redshift that the universe is expanding. Primarily the Cosmic Microwave Background and the Big Band Model. We can imagine watching the history of the universe in reverse and with an expanding universe eventually everything will come together in a single point, the Big Bang. If this is true then there was a time in the early universe when everything was the same before it spread out and formed stars and galaxies. This is what the Cosmic Microwave Background is. More precisely the CMB is an image of the universe when it was only 379,000 years old. At that time the universe entirely consisted of a hot plasma at a temperature of about 3000 K. What we see today as the CMB is the redshifted image of this hot plasma. Today we see it as a blackbody temperature of 2.73K. The incredible thing is that no matter where you look you get the same measurement with variation of only 0.000018 K. Thus we can conclude that the CMB is from a time when the universe was homogenous and isotropic, that is to say it was the same everywhere.

 

Cosmology is built around creating a model of the universe that explains everything. Its not always perfect which is why its still an area of very active research but the expanding universe is a key part of explaining numerous observations and evidence and it fits well with the theories of relativity.

[wasab]

On 7/31/2019 at 8:52 AM, Dash Lambda said:

Think of it like a gas. You know how using a compressed air can for too long will make it get really cold? If space is expanding, then the photons traveling through it get stretched out and 'colder' over time.

 

A good example is the Cosmic Microwave Background (CMB), which is light from the moment the universe went from an opaque plasma to a transparent... Something. It was extremely hot and bright at the time, but over the course of billions of years the universe/space has expanded and it's cooled down to the point where it's below the visible spectrum.

 

That's not really what we're observing. At large scales the expansion of space pushes things away, but at small scales, specifically at the local group and below, gravity and electromagnetism overpower it. At human scale they overpower it so much that it's completely undetectable.

Is heat death possible? Will entropy overtakes even the strong nuclear force and rips all atoms into elementary particles? 

[tikker]

7 hours ago, tsmspace said:

it is basically assumed that the light we see from that distance didn't hit anything first.

Which is a reasonable assumption. If I put a door between you and a light bulb, you won't see the light bulb, because the light hit the door first and was either absorbed or scattered in a direction away from you. The light can definitely have interacted with things or "hit" things on the way though. This is exploited in, for example, spectroscopy, where we scan a whole spectrum of wavelengths to look for emission and absorption (=light hit something and hence did not reach us at full intensity). If the intervening medium becomes too dense (i.e. the door), then we see nothing. If it's only something like tinted glass, we'll still see it, but at reduced intensity.

 

7 hours ago, tsmspace said:

I seriously can imagine the light losing energy along the way,

Photons actually can and do lose or gain energy in other ways! For example, they can interact with electrons in ionized gas, where they scatter off of the electrons in there and can gain energy or lose energy. This, however, does not explain away the redshift that occurs due to the expansion of the Universe.

[wasab]

On 7/31/2019 at 6:22 PM, harryk said:

Wave-particle duality is another one of those weird physics realities. We think we have it figured out but it's on the fringe of explanation. In general, light acts as a particle, a photon, when it interacts with matter. Light acts as a wave when interacts with itself or with other fields. It's really way more complicated than that, but it's a good way to think about it. 

I remember my 5th grade science teacher taught me that light is not matter. It doesn't take up space so it can't be particle and shouldn't have any mass. 

[Commodus]

3 minutes ago, wasab said:

Is heat death possible? Will entropy overtakes even the strong nuclear force and rips all atoms into elementary particles? 

That's a frequent theory of how the universe 'ends.'  However, the time scales for that are so vast that they make the entire history of the known universe seem brief.  The decay time for a supermassive black hole is 10¹⁰⁰ years, and there will likely still be matter for a while after that.

[tikker]

8 minutes ago, wasab said:

I remember my 5th grade science teacher taught me that light is not matter. It doesn't take up space so it can't be particle and shouldn't have any mass. 

For me the wave-particle duality is better interpreted as that in reality it intrinsically is neither. It just behaves like a wave in some situations and like a particle in others. One unsatisfying answer to the zero mass is that it "just" doesn't interact with the Higgs field, so it never gets mass. Another way to look at it would be that Einstein's equations tell you the (relativistic) energy of an object with mass is E= ?m₀c² where ? is the Lorentz factor ? = 1 / √ (1 - (v/c)²) and m₀ is the rest mass. This shows that for any massive object, its energy would approach infinity as its velocity approaces the speed of light, so light cannot have mass (or is not matter, as you put it).

 

[wasab]

16 minutes ago, tikker said:

For me the wave-particle duality is better interpreted as that in reality it intrinsically is neither. It just behaves like a wave in some situations and like a particle in others. One unsatisfying answer to the zero mass is that it "just" doesn't interact with the Higgs field, so it never gets mass. Another way to look at it would be that Einstein's equations tell you the (relativistic) energy of an object with mass is E= ?m₀c² where ? is the Lorentz factor ? = 1 / √ (1 - (v/c)²) and m₀ is the rest mass. This shows that for any massive object, its energy would approach infinity as its velocity approaces the speed of light, so light cannot have mass (or is not matter, as you put it).

 

But if light has no mass, then doesn't m equal to 0 and E equals to 0 as well. So light has no energy???

[tikker]

17 hours ago, wasab said:

But if light has no mass, then doesn't m equal to 0 and E equals to 0 as well. So light has no energy???

Light has momentum, which also counts towards energy. The full formula with momentum included is E² = (m₀c²) + (pc)² so even with m = 0, you'll have a non-zero energy E = pc.

[wasab]

8 hours ago, tikker said:

Light has momentum, which also counts towards energy. The full formula with momentum included is E² = (mc²) + (pc)² so even with m = 0, you'll have a non-zero energy E = pc.

P stands for momentum but isn't momentum equals to mv where m is mass and v is velocity according to netwons law of motions. So if m = 0, p is 0???

[tikker]

8 hours ago, wasab said:

P stands for momentum but isn't momentum equals to mv where m is mass and v is velocity according to netwons law of motions. So if m = 0, p is 0???

The definition of momentum as p = mv is for classical particles, photons are relativistic, so you switch to Einstein's equation above. So even in the case of something with zero rest mass (e.g. a photon, I should have clarified rest mass), we still have E = pc. You can define a relativistic mass m, such that E = mc², which will give you p = mc.

[wasab]

2 hours ago, tikker said:

The definition of momentum as p = mv is for classical particles, photons are relativistic, so you switch to Einstein's equation above. So even in the case of something with zero rest mass (e.g. a photon, I should have clarified rest mass), we still have E = pc. You can define a relativistic mass m, such that E = mc², which will give you p = mc.

I see. If photon has momentum, does it mean I can shoot light at someone like a projectile? 

[harryk]

1 hour ago, wasab said:

I see. If photon has momentum, does it mean I can shoot light at someone like a projectile? 

Sure, though the intensity of light needed to actually provide an impact will be more than enough to vaporize them outright. Though light's momentum is not negligible. There is the Crooke's Radiometer which is like a light windmill. There is also the concept of a solar sail which uses a big reflective surface to literally fly through space on the power of sunlight, or very large Earth-based lasers. Ongoing right now is the LightSail 2 mission which I believe is the first time anyone has demonstrated controllable flight with a solar sail.