Universe 'likely to grow forever'

[scooterscot]

Nothing is outside the balloon. Not even nothing, it doesn't exist.

So what's the universe expending into?

[TimberWolf]

So what's the universe expending into?

It's only expanding on the inside. There's no outside. Simples

[gingerjedi]

You might be a monkey on a rock, doesn't mean the rest of us are...

HTH monkey boy

I was predicting that sort of arrogant response from you, I'm just surprised it took you so long.

Cosmically speaking you're just a tadpole in a small pond.

[doodab]

Why do you think a universe that exhibits change is an extra dimension?

The universe is not linear, our perception of it is, this is what we call time. That does not mean it exists.

The universe is changing, there is even suggestion that the speed of light has changed since the first structures came into being.

As it says in the dictionary time "the indefinite continued progress of existence and events in the past, present, and future"

If time does not exist, how can you assert:

a) that the universe is changing i.e. that it's different from one point in time to another
b) that light has a speed i.e. travels a certain distance in a certain period of time

Human perception of time's passing as a linear flow may be just a perception, but that doesn't mean that what we perceive doesn't exist. The fact we experience past, present & future in the way we do implies something about the mathematical structure of the universe. That structure cannot be got rid of simply by considering other points of view where time doesn't "flow", such as the 4 dimensional space time continuum of relativity.

The problem with that is there is nothing to stop me recreating the events of yesterday exactly as they were, today; how would you know the difference?

The problem with that is that there are, in fact, several things that will stop you recreating the events of yesterday exactly as they were, such as the fact that nothing can travel faster than the speed of light, and the uncertainty principle.

Disregarding those, if you could recreate the past exactly, I would indeed be unable to tell the difference. This is "symmetry under translation in time", essentially the observation that the laws of physics are the same at all times. It is what leads to the conservation of energy.

This is a good example of how time is different than space. The corresponding translation in space (which can happen in three dimensions instead of one) leads to conservation of momentum.

n.b. I have an unfair advantage here as I have Einstein in my backpack

[scooterscot]

If time does not exist, how can you assert:

a) that the universe is changing i.e. that it's different from one point in time to another

Must you be so linear. If the substance of the universe can be anything why is time relevant? Time is the human way of giving name to a specific sequence of events.

If time does not exist, how can you assert:

b) that light has a speed i.e. travels a certain distance in a certain period of time

Light is the effect on particles when certain energy levels are exceeded. No different than any other particle or pattern making it's presence felt throughout the cosmos.

Human perception of time's passing as a linear flow may be just a perception, but that doesn't mean that what we perceive doesn't exist. The fact we experience past, present & future in the way we do implies something about the mathematical structure of the universe. That structure cannot be got rid of simply by considering other points of view where time doesn't "flow", such as the 4 dimensional space time continuum of relativity.

Or is it the animal in us understands past present and future because we know what happens to our survival if we ignore it. Many a Nature journal has shown why manuals have become extinct because they did not act quickly enough to evade there pursuer!

The problem with that is that there are, in fact, several things that will stop you recreating the events of yesterday exactly as they were, such as the fact that nothing can travel faster than the speed of light, and the uncertainty principle.

There's nothing in SR that's says you cant. Don't know what C has got to do it.

This is "symmetry under translation in time", essentially the observation that the laws of physics are the same at all times. It is what leads to the conservation of energy.

That's the problem, the laws of physics have been shown to change since the big bang. The known universe is around 13.7 billion light years across however in actual fact it's more likely to be around 90 billion light years across i.e. beyond the CMB, just because we cannot see it measure it does not mean symmetry is uniform.

[doodab]

Must you be so linear. If the substance of the universe can be anything why is time relevant? Time is the human way of giving name to a specific sequence of events.

I'm really not sure what you mean by "the substance of the universe can be anything".

If we are to require that our theories about the universe tally with experience, and hence we reject those theories which are flat out contradicted by things we can observe, then clearly that places some constraints on the substance & nature of the universe.

Now the problem with your opinion is that there is something "timelike" involved in the structure of the universe i.e. there is something that has the particular relationship with space that time has. We can be sure of this, because we can create mathematical descriptions of universes that don't have it, and work out how they might behave, and that disagrees with what we observe.

Light is the effect on particles when certain energy levels are exceeded. No different than any other particle or pattern making it's presence felt throughout the cosmos.

Light is electromagnetic radiation. It *is* different than other particles, actually, because it doesn't have mass and travels at the speed of light.

There's nothing in SR that's says you cant. Don't know what C has got to do it.

There is nothing to stop you doing a thought experiment, but it would be impossible to do it in reality. The speed of light is relevant because it defines the volume of space you would need to wield total control over in order to recreate the events of yesterday at a particular point in space, and because it simultaneously limits your ability to do so. It would take you a certain amount of time to propagate control signals from one side of the volume to the other, and in that time the volume would have grown (because information from further away would have had time to reach it) as least as fast as any signals you sent could have travelled, so it would be impossible for you to be fully in control of the required volume of space.

That's the problem, the laws of physics have been shown to change since the big bang. The known universe is around 13.7 billion light years across however in actual fact it's more likely to be around 90 billion light years across i.e. beyond the CMB, just because we cannot see it measure it does not mean symmetry is uniform.

I think you are confusing your numbers here. The universe is thought to be about 13.7 billion years old, but the observable universe is more than 27.4 billion light years across because of the expansion. It's reckoned to be around the 90 billion light years you state, but that space isn't "beyond the CMB", that's what we can see. There is quite possibly space beyond that that we will never be able to see because it's moving away so fast that the light will never reach us.

I'm not suggesting that we have the "laws of physics" exactly right, what I am pointing out is that we can make up alternative laws that don't have something "timelike" and work out roughly how such a universe would look, and it wouldn't look like this one. It really is a fundamental fact about the structure of the universe.

[Doggy Styles]

No. The standard way to think about it is that we are on the outside of an inflating (4 dimensional) balloon. Everything is receding away from everything else and every point is at the centre of the universe. Nothing is outside the balloon. Not even nothing, it doesn't exist.

I'd like to believe that, and I've tried, but it doesn't cut the mustard. Many years ago someone else came up with a theory that space is curved, so as you keep going out deeper into it you end up coming back from the other direction. That doesn't cut it either.

There's an infinite amount of nothing (non-existence if you like) beyond whatever spacial limits we put on the universe. Wellington in the Daily Mirror regularly boggled his mind over things like that.

[gingerjedi]

Tantalising evidence hints Universe is finite - New Scientist

Our Universe seems like an endlessly repeating set of dodecahedrons, football-like shapes with a surface of 12 identical pentagons. If you exit the football through one pentagon, you re-enter the same region through the opposite face and you keep meeting the same galaxies over and over again (see graphic, bottom).

Cornish says his team believes it has already ruled out almost half of the possible small-Universe shapes - including football and doughnut shapes - and he suspects the work will probably turn up nothing, meaning that the Universe is either very large or infinite.

[SupremeSpod]

Must you be so linear. If the substance of the universe can be anything why is time relevant? Time is the human way of giving name to a specific sequence of events.

Nope, Time is a delta linking events.

Nothing happens instantaneously.

[SupremeSpod]

Tantalising evidence hints Universe is finite - New Scientist

Cornish says his team believes it has already ruled out almost half of the possible small-Universe shapes - including football and doughnut shapes - and he suspects the work will probably turn up nothing, meaning that the Universe is either very large or infinite.

Nice work if you can get it.