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Physics, Astronomy & Cosmology / Re: Watching, hearing, playing in a spaceship travelling near speed of light

« on: Yesterday at 09:06:08 »

Should the prohibition be formulated to state that nothing  with mass may be accelerated to a relative speed greater than c?

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Famous Scientists, Doctors and Inventors / Will I post a link for some new Feynman videos here?

« on: 02/04/2021 17:00:38 »

http://www.thescienceforum.com/links/50272-newly-presented-feynman-lectures.html

I like them a lot  since they are good quality and maybe this is a good place to post a link to them?

https://www.feynmanlectures.caltech.edu/

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New Theories / Re: Is the speed of a light a consequence of ?

« on: 27/03/2021 17:50:21 »

Is the speed of light a consequence of an external force  ?

No. The speed of light is a consequence of how Space and Time are interrelated to each other. 

Do you mean it is a consequence of how spatial measurements and time  measurements are related?

"Space" and "Time" are not physical objects, are they?

Can we say they are "metaphysical"(if that description is of any consequence)

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Physics, Astronomy & Cosmology / Re: Centre of the universe?

« on: 27/03/2021 01:37:42 »

It's not an explosion "in space" but an expansion "of space

It can be both, can't it?

Can you have two or more objects  that undergo expansion of the space between their constituent parts?

They might in theory interact too.

Is there an explanation of the phenomenon whereby the space between objects (galaxies)
 increases?

Or is it just that we observe this to be the case and the inflationary model describes the process well?

Also can it be shown that the expansion of space is 100,% uniform?(does it need to be so shown?)

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Physics, Astronomy & Cosmology / Re: How does mass-energy curve spacetime?

« on: 07/03/2021 03:31:30 »

find the logic hard to grasp...there is Something, which is Nothing..but still it Curves & Bends & even Uncurves & Unbends?
Pretty Puzzling Right!

Not sure if logic is involved.

If you were to wonder (forgetting completely about gravity or curved spacetime and putting yourself back in mediaeval times) why the space between objects was "straight" ...ie Why the shortest distance between objects was  apparently a straight line ,you might well say ,"that is just how it is,no reason for it"

So ,with an environment of massive objects it turns out that the shortest distance is  apparently curved when viewed ,necessarily  from a distance

Why? Who knows ,it just is.

Just my gut feeling.

Also ,don't forget that spacetime curvature  is just a model that can and likely/hopefully  will be improved on or tweaked  in the future.

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Physics, Astronomy & Cosmology / Re: What is space & time(According to Einstein's theory of relativity)?

« on: 24/02/2021 02:41:39 »

The disk will shatter

Is there an obvious pattern in the way it would shatter?

Would it shatter in a similar way to the windscreen of a car (lots of small pieces?)

Would the size of those pieces get larger as we got further from the centre?

Oh and would you get the same /similar effect if you were using the Newtonian model?

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Physics, Astronomy & Cosmology / Re: What is space & time(According to Einstein's theory of relativity)?

« on: 24/02/2021 00:27:30 »

And physical objects seem  slippery customers when approached at the quantum level.

@Halc wasn’t talking about the quantum level, this is large scale stuff 

Yes ,but I was wondering if there might be  a symbiotic relationship** between objects and the space they exist in.

Might it not be necessary to address that question (if it is a good question) at all levels ?


(I appreciate that @Halc  's example was very concrete and entirely "large scale")

**In the sense that one might talk of an object/space duality(it is just a vague idea I have had recently)

Edit: I think this earlier thread  elsewhere (2016) that I started relates to Halc's example. I found it then in  some Feynman lecture notes on the internet.

https://www.scienceforums.net/topic/100967-physical-demonstration-of-the-curvature-of-spacetime/

Disappointingly ,though towards the beginning of the thread I was told those measurements were more theoretical than concrete .(it was a thought experiment)

No doubt there are other examples that lend themselves  to more practical ways of verification?

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Physics, Astronomy & Cosmology / Re: What is space & time(According to Einstein's theory of relativity)?

« on: 23/02/2021 23:06:18 »

Then the tape-measure thing above would not be true. It's not just pretty pictures. It's no more remarkable than showing that the surface of Earth is bent by showing that the angles of a triangle drawn on it will add up to more than 180°.  Similarly, a triangle drawn on a seemingly flat sheet near a gravity well might have its angles add up to less than 180°.

Yes,I get your point.If the contents of the space are distorted then you can say that the space itself  is also distorted .
I sometimes ask myself what is the difference between space and the objects it contains.

Some kind of a symbiotic relationship,rather  than just to say that the spatial and temporal distances are simply mathematical /physical measurements?

And physical objects seem  slippery customers when approached at the quantum level.

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Physics, Astronomy & Cosmology / Re: What is space & time(According to Einstein's theory of relativity)?

« on: 23/02/2021 16:03:44 »

I think you should not try to think of the space between two masses as being curved in any way.

It is really just the mathematical model (the graphs) that look bent.

No one knows why this should be the case  but is observed to be the case and so the mathematical model (relativity) which shows this effect (and makes incredibly accurate predictions)

As well as I have learned,space and time are treated as two sides of the same coin  and it is the  way they combine that changes when in the presence of mass or energetic processes.

Stand to be corrected as I have no formal learning apart from what I have picked up on these and other science forums.

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Physics, Astronomy & Cosmology / Re: What happens to the spacetime interval between two events as they approach a BH?

« on: 20/02/2021 14:41:19 »

So it makes no difference whether the ball is in a region of flat space or curved space?

Exactly

What about if there is a region of curved space between the observer and the ball ?(which is still falling into its own gravity well.

Yet again, it is frame invariant, and thus not observer dependent.

Digressing a bit.Is it fair or noteworthy  to say all these events in GR are treated as point objects even though they are actually spatio-temporally extensive?

Is that where a theory of  quantum gravity might be useful?

(I thought it was interesting where you said, to hopefully paraphrase- that the ball was in its own frame of reference and so any interval was purely temporal. )

 

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Physics, Astronomy & Cosmology / Re: What happens to the spacetime interval between two events as they approach a BH?

« on: 20/02/2021 04:37:52 »

the ratio of temporal to spatial is going to go from infinite (T / 0) to something finite (>T / >0).  This is all true anywhere, so no mention of the black hole is needed.

So it makes no difference whether the ball is in a region of flat space or curved space?

What about if there is a region of curved space between the observer and the ball ?(which is still falling into its own gravity well.

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Physics, Astronomy & Cosmology / Re: What happens to the spacetime interval between two events as they approach a BH?

« on: 20/02/2021 01:52:53 »

The spatial and temporal coordinates of any pair of events is coordinate system dependent, so yes, both change with a change in coordinate system (observer frame if you will).

So ,in my scenario as similar (=identical in their own frame ) pairs of events are recorded by an outside observer  does the ratio of the temporal to the spatial component of the (same) spacetime interval change as the  subsequent event pairs are observed nearer the source of gravity ?

And ,if so which component increases wrt to the other?

Since ,I have heard the time slows from the outside observer's perspective as object's approach an event horizon can I guess it to be the temporal component that increases wrt the spatial component?

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Physics, Astronomy & Cosmology / Re: What happens to the spacetime interval between two events as they approach a BH?

« on: 20/02/2021 00:46:59 »

Depends on how long it is between strikes as measured by the ball.  If it's the same time, then the interval is the same.  The two events could be on either side of the event horizon if you please. It really doesn't make a difference, except in the latter case, the outside observer isn't going to observe both events.

If the spacetime interval doesn't change does the spatial component change wrt the temporal component?

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Physics, Astronomy & Cosmology / Re: What happens to the spacetime interval between two events as they approach a BH?

« on: 20/02/2021 00:44:55 »

Then they're a different pair of events.

Yes ,I  appreciate(d) that.

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Physics, Astronomy & Cosmology / Re: How does mass-energy curve spacetime?

« on: 19/02/2021 22:28:35 »

I think it does it by reducing uncertainty but this is not the serious science answer you are asking for. Nevertheless I have not been able to shake the idea from my head that I might be right.

Why do you think reducing uncertainty and curving spacetime could be connected?

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Physics, Astronomy & Cosmology / Re: What happens to the spacetime interval between two events as they approach a BH?

« on: 19/02/2021 22:26:19 »

That shouldn't change at all. It's frame invariant, so it is the same in any coordinate system of choice.

I am talking about similar pairs of events ( say a ball striking a surface ,event#1  and rebounding and striking another surface I metre distant,event#2)

From the frame of a distant observer there is a spacetime interval between those two events.

If we repeat the experiment closer to BH  then I am asking how the  new spacetime interval compares to the earlier spacetime interval ( and how the r/t ratio developes as the experiments are made closer to the BH(or any gravitational source)

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Physics, Astronomy & Cosmology / How does mass-energy curve spacetime?

« on: 19/02/2021 04:24:43 »

I am fairly sure,based on what I have heard that the answer is that we do not yet know the answer to this.

However ,are there any serious ideas as to what the actual mechanism might be ?

I imagine it might be somehow based on  fields  since that seems to be the predominant area of theory concerning very small object's,which may be the level where spacetime curvature occurs.

But I have extremely little insight into this area.

Are there any theories or hypotheses that could make some sort of sense to a layman?

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Physics, Astronomy & Cosmology / What happens to the spacetime interval between two events as they approach a BH?

« on: 17/02/2021 16:13:28 »

....or any similar object that curves spacetime?

ie how does the r/t ratio in the s^2= ct^2-r^2  formula change?

Edit :I don't mean the same event ,of course .I mean  identical events whose spacetime intervals are measured as they approach the source of gravity.(Perhaps  light reflecting between two mirrors would do - or two hypothetical events involving massive objects)

Reedit: the event pairs  are causally connected.

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Physics, Astronomy & Cosmology / Re: did the universe begin life inside a black hole?

« on: 02/02/2021 01:59:07 »

That is a hypothesis which has been supported by a number of professional cosmologists.
- It is compatible with Einstein's relativity
- But as yet, we have no evidence that other universes exist
- And we have not yet peered inside a black hole (and even if a brave explorer did go there, they could not report back...)
See: https://en.wikipedia.org/wiki/Black_hole_cosmology

Looking at the beginning of our universe, the entire mass appears to have been in a very compact state.
- That suggests that it started as a black hole
- And since (virtually) nothing can escape from a black hole, we are probably still inside it

If we are in a black hole as you hypothesize,that implies that inside the event horizon there is a more or less infinite number of ways matter can be organized.

So it is only at the very centre of the BH that  the constituent parts of matter become amorphous  and identical to each other?

When two BH's collide  do the internal changes caused mutually one on the other propagate at the speed of light?(Can we say?)

Hope that was not too much gobledegook ;-)

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Physics, Astronomy & Cosmology / Re: Are there any serious ideas floating around about Wormholes?

« on: 22/12/2020 11:46:35 »

However, there are quantum effects in the areas surrounding black holes and would also be around wormholes if they exist. Interestingly, relativity is relevant at the quantum level.

Any particular example of how a quantum effect might have a bearing on how a wormhole would be expected  to behave (or be observed) if it did turn out that they existed in Nature?

Are there any behaviours that could be ruled out owing to the constraints of QM?

I remember how Black Holes were considered outlandish in the past.

Is there any chance that Wormholes too might be  detected in the future?