Can someone please explain galaxies moving 5 times light speed and

[Markus Hanke]

3 hours ago, Angelo said:

My assertion is that no one knows, do you know?

We know which options exist, given the validity of the laws governing gravitation (this can be worked out analytically). We then take the observational data available to us at a given point in time, and see which of these options the data fits best; this then becomes the current consensus. But this is an evolving process - as new data becomes available to us, the consensus can shift over time, as the larger data set may better fit a different option. This is the whole point of physics - it makes models which describe aspects of the universe as accurately as possible, but it does not pursue some spurious notion of “absolute truth”. A model is “true” only in the sense that it fits available data, and makes accurate predictions. As such, it is really more epistemic than ontic in nature. 

[Strange]

7 hours ago, Angelo said:

My assertion is that no one knows, do you know?

Uncertainty in measurements of the rate of expansion is not the same as “no one knows”

 

[guidoLamoto]

A couple thoughts that may help some appreciate the concepts of an expanding universe & Hubble's observations: The Big Bang Theory says that if we could travel back in time towards the origins of the universe, all matter, energy, space & time would be concentrated in a very small area (Can we get back to Time Zero, or only approach it asymptotically?) At the  moment of The Big Bang, all matter and energy started flying outward like shrapnel from an exploding grenade, but keep in mind that time & space itself started expanding-- so it's like watching someone on the moving sidewalks at the airport, too.

Now take a balloon and draw a couple dots on it and then fill it with more air-- as the balloon gets bigger, the dots move farther and farther apart from each other. Hubble, using the concept of red shift, was able to observe that. ...Now consider an exploding grenade-- all the pieces of shrapnel started moving out from ground zero at the same time, but some fly further than others. Those that land farthest away must have been travelling the fastest....Because space itself is expanding, and the space farthest away, just like the farthest shrapnel is expanding the fastest, so the farthest galaxies, travelling at acceptable speeds in their own piece of local space, like the pedestrians on the moving sidewalk, look like they're moving faster than light to us in our own frame of reference.
 

[swansont]

1 hour ago, guidoLamoto said:

A couple thoughts that may help some appreciate the concepts of an expanding universe & Hubble's observations: The Big Bang Theory says that if we could travel back in time towards the origins of the universe, all matter, energy, space & time would be concentrated in a very small area (Can we get back to Time Zero, or only approach it asymptotically?) At the  moment of The Big Bang, all matter and energy started flying outward like shrapnel from an exploding grenade, but keep in mind that time & space itself started expanding-- so it's like watching someone on the moving sidewalks at the airport, too.

The grenade/shrapnel description is a common mischaracterization, as it shows an explosion in space rather than explosion of space.

 

[Mordred]

I believe your stated that wrong above lol.

4 hours ago, swansont said:

The grenade/shrapnel description is a common mischaracterization, as it shows an explosion in space rather than explosion of space.

 

I believe you meant "rather than an expansion of space" for the latter.

[swansont]

8 hours ago, Mordred said:

I believe your stated that wrong above lol.

I believe you meant "rather than an expansion of space" for the latter.

That's perhaps a better description, but when "explosion" is used by folks who have some knowledge in the matter, people say "explosion of space" to differentiate the ideas and rebut the "shrapnel" description, and the notion that some chunks simply "exploded" faster than others.

 

In case anyone's interested, a few examples:

https://www.amnh.org/exhibitions/permanent/the-universe/the-universe/the-big-bang

https://www.nbcnews.com/mach/science/universe-may-be-billion-years-younger-we-thought-scientists-are-ncna1005541

"This is another hard concept for people to get their heads around," University of Chicago cosmologist Wendy Freedman said, adding that the Big Bang didn't go off like a kind of bomb. "The Big Bang is an explosion of space, not into space," she said.

[Mordred]

Ah kk, I always found expansion more accurate. As it describes the homogeneous  and isotropic nature of expansion better.

An explosion has a directional component so you would be inhomogeneous (Ie have a point of origin and anistropic (preferred direction). This would result in angles changing between galaxies which is discounted by observational evidence. The angles are preserved as the distance between galaxies increase.

 

[joigus]

On 1/7/2020 at 9:14 PM, Angelo said:

Space is a constant,

How can a continuum be a constant? Could you elaborate on that? Maybe you're on to something. 

Can a stone be unhappy? See my point?

On 1/7/2020 at 9:14 PM, Angelo said:

There is no absence of gravity where mass is concerned

If there is **one** feature of gravity that singles it out from every other force in the universe is the fact that you can always locally achieve absence of gravity (equivalence principle, EP). The only limit to this is second-order effects, AKA tidal forces. Jump off a window and you'll find out about EP. Get close to a relatively small black hole and you'll find out about tidal forces. Read a good book and you'll find out about how this all adds up. Oh, and mass is not concerned at all in GTR, as it plays no role in the theory. It's all about energy. It's energy that provides the source of the field. What you call mass is just rest energy, and this is no battle of words. Photons of course have no mass because they have no rest energy; and they have no rest energy because... well, they have no rest.

 

On 1/7/2020 at 8:04 PM, Angelo said:

how relativity which explicitly says that nothing with mass can travel faster than the speed of light

Incorrect: Special Relativity (SR) says nothing (massless or not) can travel faster than the speed of light.

Because GTR says geometry of space-time must locally reduce to SR, things moving locally can't exceed c. In other words: things moving past you can't do so at faster than c. 

People here have been quite eloquent so I won't belabor the point.

I don't want to be completely negative. My advice is: Read some books, with a keen eye on experimental results; then do some thinking; then read some more books; then some more thinking, and so on. Always keep an eye on common sense too. Listen to people who seem to know what they're talking about, ask nicely for inconsistencies and more information, data. Always be skeptic, but don't just be skeptic. It doesn't lead anywhere.

Edited May 4, 2020 by joigus
mistyped

[Strange]

55 minutes ago, joigus said:

Photons of course have no mass because they have no rest energy; and they have no rest energy because... well, they have no rest.

Busy, busy, busy. Places to go, people to illuminate

56 minutes ago, joigus said:

Always be skeptic, but don't just be skeptic. It doesn't lead anywhere.

Nicely put.

I get the impression that some people read books/articles (and answers on forums like this) having decided they are all wrong and just looking for things they can disagree with.

[joigus]

32 minutes ago, Strange said:

Busy, busy, busy. Places to go, people to illuminate

Nicely put.

I get the impression that some people read books/articles (and answers on forums like this) having decided they are all wrong and just looking for things they can disagree with.

My same impression.

[Area54]

38 minutes ago, Strange said:

I get the impression that some people read books/articles (and answers on forums like this) having decided they are all wrong and just looking for things they can disagree with.

I can't agree.

 

 

@Angelo You are missing a great opportunity to learn from some knowledgeable people. Don't pass it up for some lightweight reason.

[swansont]

51 minutes ago, Strange said:

Busy, busy, busy. Places to go, people to illuminate

Massless bosons gonna massless boson.

 

[dimreepr]

1 hour ago, swansont said:

Massless bosons gonna massless boson.

Time on this site really does help, I get the joke. 🙂

Edited May 4, 2020 by dimreepr