Can Black Holes Exist?

[Rootje]

Ok, a black hole (presumably) is a star which has collapsed to a single point, a singularity in which all the mass of the star is concentrated. A lot of their properies (like twisted spacetime when they rotate or X-ray energies in the centre of accretion disks, in accordance with their mass and zero diameter) have been theorized and some even observed. But all around the fact that a black hole has almost zero diameter.

 

But when a star collapses beyond the density of neutron stars, it keeps on collapsing till it reaches its event horizon diameter. According to general relativity, its time w.r.t. the rest of the universe comes to a complete stop. How is it then possible for the black hole to collapse further to a singularity, if its time is frozen?

[ydoaPs]

wait, explain why the rest of the universe would come to a complete stop.

[Rootje]

wait, explain why the rest of the universe would come to a complete stop.

 

its time w.r.t. the rest of the universe comes to a complete stop. Because of the relativistic time dilation in the presence of a strong gravity field...

 

The time of the rest of the universe would just flow as usual.

[Sayonara]

I think we need more threads on this. Not fewer, more.

[JHAQ]

For anything transitting into a black hole , time seems normal . It is only to an ouside observer that time seems to stop FOR THE OBJECT transitting & such objects at the event horizon appear frozen in time. My question would be that for any such object , its mass- energy becomes infinite & if infinite is infinite , why is the universe still here ?

[Jacques]

Welcome Rootje

I am also new here but I posted the same question http://www.scienceforums.net/forums/showthread.php?t=8289

 

I think that most people are certain that blackhole exist.

JHAQ

It is only to an ouside observer that time seems to stop

We are all outside observer. Universe been a finite time, so no singularity had time to form.

mass is not infinite, the density is (in blackhole theory). So we have the effect of the mass of the black hole.

Some are suppose to be suppermasive at the center of galaxies. Many many million solar mass! Near the center of a galaxie very violent phenomena are detected in X ray images. Motion of the star need big mass there.

[Rootje]

Remember the Twin paradox? The twin that's been traveling at lightspeed (rel. to earth) returns years younger then the one that stayed behind.

 

The one that stayed behind is like any outside observer. So indeed, in the black hole case, before an actual singularity is formed in the centre of the star the entire lifetime of the universe flashes by. And even if you wait until the end of existence to see a singularity, Hawkings-radiation has vaporized the black hole again.

 

I think black holes do exist, but not in singularity form, just a very very heavy object in a very very small volume. The volume of the theoretical event horizon yes, but no smaller.

 

Or .. am i wrong ?

[[Tycho?]]

Remember the Twin paradox? The twin that's been traveling at lightspeed (rel. to earth) returns years younger then the one that stayed behind.

 

The one that stayed behind is like any outside observer. So indeed' date=' in the black hole case, before an actual singularity is formed in the centre of the star the entire lifetime of the universe flashes by. And even if you wait until the end of existence to see a singularity, Hawkings-radiation has vaporized the black hole again.

 

I think black holes do exist, but not in singularity form, just a very very heavy object in a very very small volume. The volume of the theoretical event horizon yes, but no smaller.

 

Or .. am i wrong ?[/quote']

 

You can assume you are wrong youself, actual physicits came up with these theories and hav held for decades. Its safe to assume that their opinion is worth more on this than yours, hence if its a question between them being wrong and you being wrong, its you thats wrong.

[ecoli]

'']You can assume you are wrong youself, actual physicits came up with these theories and hav held for decades. Its safe to assume that their opinion is worth more on this than yours, hence if its a question between them being wrong and you being wrong, its you thats wrong.

 

That's a funny thing to say on a science forum. The whole point of it is to debate what scientists say. I'm sure you've done the same, on occasion.

[The Rebel]

That's a funny thing to say on a science forum. The whole point of it is to debate what scientists say. I'm sure you've done the same, on occasion.

 

I think we trust scientists too much, everyone can be wrong just as much as right. Countless numbers of theories have been proven and disproven.

 

One of the reasons I have given my name as The Rebel is because I do not believe some of stuff science has come up with, its half written and unsubstantiated sufficiently. I like to pick holes and seek the truth (from the assumed/unfounded) that way.

[swansont]

'']You can assume you are wrong youself, actual physicits came up with these theories and hav held for decades. Its safe to assume that their opinion is worth more on this than yours, hence if its a question between them being wrong and you being wrong, its you thats wrong.

 

Assuming you're using the "professional opinion" definition, and not the "I think Julia Roberts is a great actress" definition, I tend to agree. To come along and, with relatively (as it were) little study of the topic, think you've pointed out a major flaw in things that have been studied for quite some time, is hubris. GR is some fairly heavy-duty physics. What you might absorb from the web or pick up on the streetcorner is pretty watered down and missing a boatload of detail and rigor (i.e. math)

 

As far as all this discussion goes, AFAIK the only thing that matters is what the outside observer sees, not what a particle falling into the proto-black-hole sees. Since the outside observer presumably is not moving nor is in a gravity well, time does not slow down for him/her.

 

When you accelerate unstable particles to high speeds, the don't decay as rapidly, but they still interact. Their own clocks run slow, but the particles themselves don't run in slow-motion.

[[Tycho?]]

Assuming you're using the "professional opinion" definition' date=' and not the "I think Julia Roberts is a great actress" definition, I tend to agree. To come along and, with relatively (as it were) little study of the topic, think you've pointed out a major flaw in things that have been studied for quite some time, is hubris. GR is some fairly heavy-duty physics. What you might absorb from the web or pick up on the streetcorner is pretty watered down and missing a boatload of detail and rigor (i.e. math)

[/quote']

 

Exactly. Around the time I joined these forums, in the space of a month there were like 5 people who came in and claimed to know that relativity was in fact wrong. I have absolutely no tolerance for that sort of thing, people who assume that by thinking about it for 10 minutes they have seen a flaw that a century's worth of physicsts have not.

 

Unless you have studied physics at a university level, pretty much any "ideas" you have are going to be totally worthless.

[RICHARDBATTY]

But if people like us don't post here, you would not be able to show how wise and powerfull you are. An explanation of why Rootie was wrong would have been enough to enlighten though. Thats why I think a lot of people visit this site. Its an interesting subject they have not had the option to study.

[Sayonara]

I like the ones who explain the obvious gaping flaws in relativity using flash animations that make no sense.

[timo]

>> An explanation of why Rootie was wrong would have been enough to enlighten though.

 

^^ Well, that´s quite hard because as far as I can see it Rootje is completely right. Within the approximation of the Schwarzschild metric every particle of the star will reach the singularity within finite Eigentime and will not ever pass the event horizont for an outside observer.

 

 

However, there are three points in this statement I´d like to mention:

 

1) It is not possible to make a distinction between a spherical symmetric mass with r=rs and a spherical symmetric mass with r=0 for an outside observer. But that was also allready said by Rootje.

 

2) It is said (and way beyond my understanding of GR) that not only a spherical symmetric mass distribution like in the Schwarzschild metric but a great range of conditions will lead to a sapcetime singularity. I would not bet that all these conditions involve infinite observer-time for the forming.

 

3) The perhaps most important point: The outer Schwarzschild metric is not a valid coordinate system for the whole spacetime of a spherical symmetric mass. While it is (at least to a good approx) the system that we observe in it might be a bit of a philosophical question whether things that we never observe -like the mass crunshing to a singluarity- do exist or not. From out point of view nothing ever passes the event horizont. Every particle of the star, however, will -from it´s point of view- fall into the forming singulariy within finite Eigentime. This reaching of the singularity within finite Eigentime is a frame-independant statement so we (the physicists) say that´s what happens. The statement that nothing ever passes the event horizont is frame-dependant and thus not phyiscally meaningfull (though it might have some meaning for you, but phyiscs isn´t very concerned about your needs ).

To sum it up: The non-collapsing of a star as seen from an outside observer in the Schwarzschild metric is an effect of an invalid/incomplete map of the universe.

[boxhead]

it is not important that whether black hole exists or not but the most important thing is that can we detect it if it exists and since time flows at normal rate in outside universe it is almost impossible to prove it. still we can make quite good assumptions and can prove theories but still it wont work.