Re: The speed of light, etc
 

On the balloon analogy:

That just doesn't wash. In that analogy, the matter in the universe is on the outer perimeter with nothing inside. The universe we are observing is full of stuff. What have I misunderstood?

Re: The speed of light, etc
 

The balloon analogy does have problems but there isn't really a better one. You need to learn the math for a better understanding - which I never have done btw.

Re: The speed of light, etc
 

You're probably right in that it should have matter represented inside it also, a bit difficult with a balloon. It just shows rather crudely that everything is moving away from everything else. That said it's a 4D (apparently) representation of space-time not just space so perhaps the inside is the time vector and the surface represents 3D space. Difficult to represent 4 dimensions using 3.

Re: The speed of light, etc
 

But what the heck is "space-time"? 3D is quite simple, with a force causing or having caused expansion. Time in this context is the number of time unit (seconds, minutes, years, etc) for a galaxy to move from 3D location "A" to 3D location "B".

In my assessment, for what it is worth, "space-time" is a confection of convenience for scientists who know quite a lot about the square root of all this, but not the bit underneath it all.

"Time vector" - don't we all understand this as time moving in one direction only? As in forwards? It has to be measured by some entity that can do such measurements or imagine them with a sound basis in fact. "Space-Time" - includes a "time vector"? Might as well be a triaxellated amplification of a sub-space message from Starfleet.

Imo!

Re: The speed of light, etc
 

I think someone mentioned the raisin bread analogy as an alternative, which I actually think is a better one as that does describe for matter on the inside.

Re: The speed of light, etc
 

Do the raisins expand in space-time? When an analogy is provided, it's usually intended to simplify a more complex situation to help understand what's going on. But really (and absolutely), no such analogy has any bearing on the universe's forces.

That's why I say we should apply logic to the question of the speed of light and what we can see in the universe.

The frequency shift of light emanating from a moving object proves (to me at least) that the speed of light is fixed.

In the theory of accelerating universe expansion, the logical situation is that somewhere, everything is moving away from us (ignoring local gravity effects) and some galaxies are approaching recession speeds that cannot be measured with existing detection systems. If the universe's expansion is truly accelerating, then the corollary is, that, relative to us as an observer, some galaxies are receditn at a speed faster than light. A lot of bottoming out still to be done!

Re: The speed of light, etc
 

Well, that’s a fascinating point, and it touches on some of the fundamental aspects of relativity and cosmology. But let’s break it down carefully.

You're absolutely right that analogies, while useful for simplifying concepts, don't alter the fundamental laws of physics. They help us build intuition, but ultimately, the universe follows mathematical principles that don;t depend on our human need for simplification.

Now, regarding the speed of light, yes, the Doppler effect, or more specifically the redshift of light, is strong evidence that the speed of light is constant. This is central to Einstein’s special relativity, which tells us that the speed of light in a vacuum is the same for all observers, regardless of their motion or the motion of the source of the light.

As for the accelerating expansion of the universe, this is where general relativity comes into play. Space itself is expanding, and that’s not the same as objects moving 'through' space. When we talk about galaxies receding from us faster than the speed of light, we’re not violating relativity because it's not the galaxies themselves moving at superluminal speeds through space; rather, the space between us and them is expanding. This means that light from these galaxies will nevre reach us, because the fabric of space is stretching too quickly for the photons to make headway.

So, in a way, we have a sort of observational horizon, the so-called 'cosmic event horizon'. Beyond this, light from galaxies can’t reach us because space is expanding too fast. This is a direct consequence of the universe's expansion being governed by what's called 'dark energy', which is driving this acceleration.

Now, your intuition that we still have a lot to work out is absolutely correct! We don’t yet fully understand what dark energy is, or why the universe’s expansion rate changed over time. But the mathematical framework of relativity does an incredibly good job of describing what we 'can' observe. But there's nothing to say that what we can see is everything that is there.

So yes, there’s definitely a lot of bottoming out still to be done, but people far more clever than myself making good progress, I should think.

Re: The speed of light, etc
 

Re: The speed of light, etc
 

Correct, there is no certainty it exists. It is just the best explanation (that dark matter does not interact with light, but does have mass, as something is holding things together) that fits the driven theories used in physics (Newton’s laws of motion and Einstein’s theory of relativity). Keep in mind dark matter has not been show horned into the theories, more the observations in relation to the theories show that something is missing. It’s the most logical answer to what is being seen.

The other option is that physics needs a new theory, such as Modified Newtonian Dynamics.

Re: The speed of light, etc
 

Although reading this thread is still giving me a headache :) I find it fascinating, and I am never surprised, by our member's depth of knowledge when they get to discuss/debate subjects outside of the normal scope of the forum. Respect to you all. :nworthy:

Re: The speed of light, etc
 

Re: The speed of light, etc
 

Nothing can travel faster than light in space/matter. Space creation isn't subject to this limitation, I'm not pretending to understand it, the maths presumably allows it to be true.

Re: The speed of light, etc
 

Re: The speed of light, etc
 

Because the galaxy’s absolute velocity is not greater than the speed of light. The distance between that galaxy and us may be increasing at greater than the speed of light because we are moving away from the galaxy at speed, just as it it’s moving away from us. But neither object is moving at greater than light-speed if observed from a fixed point.

There is a concept called the ‘future light cone’ - the region of spacetime within which nothing is moving at greater than light-speed relative to us. Anything light-emitting within this region can be observed by us. But anything whose speed relative to us exceeeds light-speed, was never within our future light cone, and never will be.

Re: The speed of light, etc
 

OK. <, sigh>> Skip to my final comment and don't feel you have to read/reply to this as it's probably a silly question and, as before, being totally irrelevant.

If there was a straight line from A through B & C to
point D. (Have I lost you yet)

1) I am on point A with a speedometer oh and a mahoosive telescope.

2) If I were able to see points B & D, point C being invisible (big bang or whatever) and .......

..... I can see B & D are moving apart from each other at the speed of light what would my speedometer register as the relative speed that they were travelling apart...... I am assuming super dooper planets could move that fast :dunce:

Give up reading now unless you want the same headache as I have.

3) My head is seeing 2 cars, driving in opposite directions, passing at 30 mph surely they would be moving apart at 60 mph

Off to go and lie down in a dark room.

Add// Just realised I'm probably confusing the speed of light with the speed of sound but I have spent so much time pondering about all this that I blowed if I'm going to delete the sodding post!!!!!!!!!!