Big Black Holes

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Baby Black Hole by Nasa

This is an open question to anyone who might understand astrophysics better than me (which is probably most of the human race).

Assume there is a really big black hole. So large, in fact, that its event horizon is more than one light-year across. If you do the sums, the gravitational force near the event horizon of such a large black hole would roughly be about 1g – the same as what it is on earth.

Imagine coming close to this event horizon in a spaceship. It would be easy to accellerate away – after all, the gravitational force in the vicinity is only 1g. So any imaginary spaceship capable of escaping the gravity of earth – if it were near the event horizon of this super massive black hole, would be able to escape its gravity.

One of the horrors you normally hear about black holes is the tidal forces that would “tear you apart”. This is caused by the difference in gravitational forces as you move closer to center of gravity of the black hole. The same thing happens near neutron stars. Your head is being pulled with a lesser force than your feet. So you get “stretched”. But in our thought experiment, the centre of gravity of our supermassive black hole is over a light-year away. My head won’t feel any different amount of attraction than my feet would. There would be no noticeable tidal forces to speak of.

So imagine you’re sitting in your late-model spaceship, orbiting just outside the event horizon of this super-massive black hole. You don’t feel any tidal forces, and the black hole is exerting a similar gravitational attraction on your vessel as what you’d experience orbiting the earth.

Apart from the huge black sphere blocking half of the sky, and the strange lense-like effect of light bending as we look across the horizon of the black hole to the numerous stars in the distance, there’s nothing to be afraid of is there?

My point is it would only take a reasonable amount of thrust to move our vessel away from the black hole.

BUT… imagine as we sit near the event horizon, we move slowly towards it until we have moved INSIDE it. What would happen? What would we experience? My meagre understanding of physics leads me to think that the escape velocity just outside the event horizon would be slightly less than the escape velocity just inside the event horizon.

So the burning question then is why couldn’t you escape from this super-massive black hole, having visited the forbidden area just inside the event horizon? The gravitational attraction at this distance would be small enough for our ship to thrust away.

And this leads me to another question. If the gravitational force near this super-massive event horizon is about 1g, why couldn’t light escape from an object just inside the event horizon? And if light could escape, would there even be an event horizon? The “Black Hole” appearance of this thing is based on the assumption that no light can escape from it because the required escape velocity exceeds the velocity of light.

So please help me. I obviously know nothing about black holes. I must be making an incorrect assumption. I don’t mind asking stupid questions, and am hoping that a patient genius will take the time to reply and explain where I’m going wrong.

Thanks in advance

ObSrv – Appropriate Images Please

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I’ve added a mandatory “Safe Search” filter to all images served up by ObSrv.

To most users, you won’t notice any difference, but the problem was that some people were using ObSrv to generate adult images, which got me in trouble with Google Adsense.

This is a business decision, not a moral one. Using ObSrv to generate adult images would get my Adsense account cancelled. No Adsense income = No ObSrv. Everyone would lose. So the simplest solution I could find was to block anything that didn’t pass the Google “Strict Safe Search” test.

If you find your image feeds aren’t generating images any more, please consider using less adult-related search terms.

Low-res Brain

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Thought experiment.

Close your eyes and imagine a clock face with hands and numbers.

Imagine the clock face as a whole.  Try not to think of just parts of it.

In your minds eye can you see the individual numbers on the clock face all at once?

I can’t.

I have to “zoom” in to each part of the clock to see all the numbers. I can’t see them all at once.

If the brain can’t do this while we’re awake, then it’s no wonder we don’t have vivid details of items when we’re asleep and dreaming.

If our brains imagery has such low resolution, why do we seem to have such hi-resolution memories?

Maybe it’s different for you.  But that’s how it is when I try it.

This whole experience helps me understand how my brain visualizes things.  It’s not like the “Pictures” folder on my computer.  I don’t store high-resolution pictures in my head.  I think it’s more like a short-hand way of reconstructing a picture.  Without realizing it my brain says  “A clock is a circle.  And it’s got numbers around it from 1 to 12.  And it has hands.  And it ticks”.

Perhaps it’s like that for someone’s face as well?  Do you know every freckle, mole or scar on your partners face?  When you think about it, how much detail of someone’s face do you actually remember?  I think perhaps we actually store a low res “caricature” of a persons face in our brain, and when we see that person, we match what we see of their face with the low res memory of it, and somehow our brain can recognize that the two things represent the same person.

I think our physical perception of reality is a lot less detailed than we realize.  When we look at a page in a book, there’s only a small circle of our vision that can actually see fine detail – about the width of our thumb held at arms length.  If you hold your thumb in front of a book held at arms length, and focus on your thumb, you’ll find it almost impossible to read the book.  That’s because the Fovea (the bit that sees detail)  in your eye only occupies a small part of your Retina (the bit that actually sees things).  But our brain manipulates us to think that we can see everything in detail, because our eyes dart around, and our brain puts all the jigsaw pieces together.

So next time you’re certain you saw something, remember that what you saw, what you thought you saw, and what you remember seeing are all totally different!

Isn’t the brain an amazing thing?

Problems Activating and Updating Windows 7 behind an Endian Firewall

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I have had problems Activating and Updating Windows 7.

I have an Endian firewall appliance.

The main error I was getting was 0×80072EFD – unable to connect.

For me, the solution (after hours of heartache) was simple:

Go into Control Panel / Network and Internet / Internet Options / Connections tab / LAN Settings,

UNTICK “Automatically detect settings” and press OK.

Activation then works.

Updates then work perfectly.

Sorry – I’m not sure why this happens. I suspect it’s a bug in Endian version 2.2 which is fixed in later a version, probably relating to the internal Endian Proxy server which in my case is disabled anyway.

I hope this helps someone.

Many thanks to my son, Lachlan, who also had this problem, and figured out how to fix it after several days of heartache.

ObSrv Performance Improvements

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I’ve improved the load speed of the ObSrv home page. Sometimes it would take a long time to load.

I’ve also improved the speed of the image feeds. It still can be sluggish at times – that’s because it’s heavily used, but to counteract this, the Image Feed will ignore requests from the same computer if they come more frequently than about once every 3 or 4 seconds.

For most people this won’t be a problem, and the only time you really notice delays on the Image Feed is if you try and display it in your browser.

If site performance is still an issue for you, please let me know.

Around Pine Rivers

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Here’s a brief description of each of the photos in the “Around Pine Rivers” theme for iGoogle.

If you’ve got any suggestions, corrections or improvements, please let me know.

Click on the images for a larger view.

Bell’s Scrub is the only remaing parcel of virgin lowland vine rainforest in the Pine Rivers district.

See http://blog.neilennis.com/index.php/bells-scrub-lawnton/

Some of the stunning late afternoon views in my street.

see: http://blog.neilennis.com/index.php/everyday-beauty/

Fleeting glimpses of childhood on the North Pine River.

See http://blog.neilennis.com/index.php/fleeting-glimpses-of-childhood/

Christmas Beetle.

See: http://www.flickr.com/photos/magictyger/sets/72157603351606109/

Wikipedia Article: http://en.wikipedia.org/wiki/Anoplognathus_pallidicollis

Lightning in the Gum Trees.

See: http://blog.neilennis.com/index.php/lightning-in-the-gum-trees/

Ebert Family Vineyard.

See: http://blog.neilennis.com/index.php/echoes-in-the-vineyard/

Stephen Lawn Park.

See: http://blog.neilennis.com/index.php/nuts-about-history/

Lake Samsonvale.

See: http://blog.neilennis.com/index.php/lake-samsonvale-2/

Wikipedia article: http://en.wikipedia.org/wiki/Lake_Samsonvale

South Pine River near the site of the old Normanby Rum Distillery.

See http://blog.neilennis.com/index.php/bikes-rivers-old-rum/

Yebri Creek.

See http://blog.neilennis.com/index.php/exploring-on-sunday/

Sunset on the North Pine River.

See: http://blog.neilennis.com/index.php/sunset-on-the-north-pine-river/

Lake Kurwongbah.

See http://blog.neilennis.com/index.php/cycling-by-the-lake/

Here’s a wikipedia article: http://en.wikipedia.org/wiki/Lake_kurwongbah

ObSrv: Why only 21 images at a time?

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Aaron asked a good question they other day.

Why does ObSrv only ever return 21 images at one time?

I thought it was a bug in my code, but it’s not. ObSrv pulls images from Google Image Search, and Google only ever returns 21 images in one go.

But this is not a problem. The images are embedded into a MediaRSS feed. That feed is cached for a maximum of one hour. After this time if you request the same feed, ObSrv will search again, but will only show images that it didn’t show last time. In the unlikely event that it runs out of images, it starts searching from the beginning again.

So although there’s nothing I can do about the 21 images at a time issue, it’s not a major problem because you will get more images after the feed refreshes – but remember, to save server resources (and to stop Google from banning me) it waits an hour between doing searches on the same terms.

On Yer Bike!

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View Larger Map

I took Steve and Harrison on a bike ride this morning, along the North Pine River, up to Lake Samsonvale, and then back along the North Pine Rover.

It was a hoot! A little bit slower than normal, because Harrison is only 9 and his bike is a bit worse for wear. But it was fun all the same.

And I got to try out a new program for my Nokia N95 mobile phone. Nokia Sports Tracker Uses the inbuilt GPS on the phone to record speed and height info. While you’re cycling, your N95 acts like a speedo, and odometer, showing you all the vital stats. But when you get home, you click the button, and upload the data to sports tracker.

The really cool thing is that if you take any photos with the phone on your journey, it will upload and geotag them.

So the map on the left here is where we went. You can drag and zoom it if you want more detail.

But the fun part is that the data is also uploaded to the Sportstracker community. Here’s a link to the data for our ride today. If you tick the “altitude” box, you can see every hill, and how fast we were going.

The thing I like most about this technology is that it adds to the fun of getting out and exercising. At times I’ve found it hard to overcome my inertia to regularly exercise. In regards to exercise, if it makes me think “Oh yeah! I want to do that again!” then I think it’s a great thing.

Oh – and you can use Sports Tracker for running, walking, skiing, rowing – whatever floats your boat.

P.S. I’ve ordered a mounting bracket to attach my phone to my handlebars. Till that arrives, I’m using some of Lilly’s hair ties

Flickr RSS Feeds. Too big, too small

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In this article about using slideshows in wordpress I showed you how to embed slideshows in Wordpress blog posts and sidebars using the Google Ajax Feed API.

I prefer to use this facility to pull in Image feeds from Flickr.

The problem with the images in these feeds is that they’re either too large or too small.

The MediaRSS specification has a tag which lets you have a thumbnail image in your feed. That’s great, but the image size of the thumbnail is 75×75 pixels, which is useless for a nice looking slideshow. It ends up looking terribly blurry with no detail.

The Google Ajax Feeds API tries to get around this by letting you specify a “thumbnailTag” in the slideshow options object. Basically, you set this to “content” to tell the API to look for the image in the “content” section of the feed, rather than the section. This is also great, but the problem is that Flickr uses the LARGE (or even worse, ORIGINAL) image size in this section. So you get nice large detailed images in the feed, but they’re so large that they take ages to load, and your slideshow sits there for ages saying “Loading….” while it grabs the huge images and chews up your audiences bandwidth.

So I wrote a simple PHP screen scraping utility which grabs the Flickr feed, and changes the ImageUrl…_L.jpg to ImageUrl….M.jpg – in other words, it modifies the feed to include the medium size image rather than the large size.

Medium sized images are fine for slideshows, and they load quite quickly.

Here’s the PHP code:


<?php
date_default_timezone_set('UTC');
$uri="";
$first_var = "1";
foreach($_GET as $variable => $value)
{
if ($variable == 'uri')
{
$uri = $uri . $value;
}
else
{
$uri = $uri . "&" . $variable . "=" . $value;
}
}
header("Content-Type: application/xml; charset=ISO-8859-1");
$ch = curl_init() or die(curl_error());
curl_setopt($ch, CURLOPT_URL,$uri);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$data1=curl_exec($ch) or die(curl_error());
$data1=str_replace("_s.jpg","_m.jpg",$data1);
$data1=str_replace('height="75"', "",$data1);
$data1=str_replace('width="75"', "",$data1);
echo $data1;
echo curl_error($ch);
curl_close($ch);
?>

Just save this in a file named FlickrRSS.php in the top folder of your wordpress directory. Then instead of using your flickr RSS feed, pass the feed as a query parameter to the PHP utility.

You’ll need to change the <> tags in the file to <>.

So if your feed URL was this:

http://api.flickr.com/services/feeds/photos_public.gne?id=8575807@N07&lang=en-us&format=rss_200

Use this instead

http://YourBlogUrl/FlickrRSS.php?uri=http://api.flickr.com/services/feeds/photos_public.gne?id=8575807@N07&lang=en-us&format=rss_200

This will change the tag to point to the lager sized image, so your slideshows will load quickly, and look nicer

Cool technology

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Lilly came in to my office the other day. “Dad I have to go out now. Can you get the TV to record my favourite show in an hour”.

“Hmmmm????”, I replied in typical pre-occuipied father mode.

But she had an intensity in her eye that made me realize I ignored this six year old at my peril, despite my displike of leaving my desk while in the middle of solving a problem.

Happily, I didn’t have to get up from my chair. I just logged in to IceTV, found the program she was interested in, and told my PVR to record it via the website.  My PVR is a High-Definition Beyonwiz DP-S1. It’s wireless, but I’ve wired it in to the house LAN so we can watch movies from our D-Link DNS323 1TB NAS

We also have an older Topfield 5000 PVRT.  It’s only standard definition, but the cool thing about it is that it has an open programming interfacem , so a lot of people have written their own software to get it to do cool things.  One application I added to it was ToppyPC by John De Angelis.  It has a program called “TWIN” which adds a web page to your Topfield PVR.  So you can set timers, and record shows, like IceTV lets you do with the Beyonwiz.   ToppyPC needs another utility to run – an FTP server (ftp4t by Aldarin) which runs on a PC which I connect to the Topfield via a USB cable.

All this technology is both good and bad. It’s convenient, but I don’t get the exercise I need going up and down stairs to program the PVR!

But at least I don’t have an angry six-year-old to contend with!

Some amazing facts

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I just watched this fascinating Youtube video. The world is an amazing place!

My Inbox

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Neil's empty inbox - a rare event

 

Isn’t this beautiful?

I haven’t seen an empty inbox for years, and I love it! When it’s full I feel like I have the cares of the world on my shoulders. But when it’s empty, it’s like I’m making progress. Even if it might be illusory, I like that feeling.

So I’m going to persist in my strategy which can be described simply as:

If it’s junk, get rid of it.

If it’s someone elses problem, forward it.

If it’s worth reading, read it now, then delete it.

If it needs more info, request more info and delete it.

If it needs acting on, then act on it now, then delete it.

Slideshow from RSS for Wordpress

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Loading…

It took me hours to find, but the easiest way I found to build a slideshow from a MediaRSS feed and add it to a WordPress blog was using the Google Ajax Feed API.

There are a few plug-ins that are supposed to work with WordPress, but I didn’t like them because they were really limited, or didn’t work on an IIS hosted blog. Good old Javascript, although it’s verbose, works fine.

That’s what I’ve used on this blog. Have a look at the slideshow on the lower right. It’s generated by the Google Ajax Feeds API.

If you don’t like getting your hands dirty with JavaScript, the best Flash based slideshow generator I know of is at VuVox.com. That’s what I use for some of the ObSrv examples of slideshows here.

The beauty of building a slideshow from an RSS Feed is that you don’t need to have the images on your own site, and the content updates continually as more items are added to the feed.

Of course, sometimes it’s hard to find a good feed. That’s where ObSrv.com comes in, because it can generate a feed from a google images search.

So when you use the Google Ajax Feed API and ObSrv.com you can make a slideshow of any topic you’d like. The one on this site is for “Information Technology”.

And just to make this post pretty, I thought I’d include a slideshow of the most recent ten pictures from the Creative Commons group on Flickr

We've Moved!

This blog has moved!

The new address is

http://tech.NeilEnnis.com

Please update your browser and RSS reader to the new links. All of my existing articles have moved too.

I'm now using WordPress as my blogging platform, and really like it.

If you've got any comments or suggestions, please let me know.

Using Twitter

A few friends have asked me to explain twitter.

Rather that re-invent the wheel, I thought I'd upload a few links that explain what it's all about.

1. The official Twitter Help Resources / Getting Started

2. How to Use Twitter Without Twitter Owning You - 5 Tips (Tim Ferriss)

3. How to Use Twitter (Darcy Logan, includes great short video)

4. Newbie's guide to Twitter

5. Twitter Fan Wiki (Sort of like Wikipedia for Twitter)

6 HashTags

Actually HashTags deserve a post all of their own. I'll post something about that later.

I hope these links help. The bottom line for Twitter I think is to follow people who have something interesting to say. Don't just follow anyone, because then the interesting comments will get drowned out with "noise".

And the converse is that it's important make your posts useful. Say stuff that will be interesting to people who follow you. Here's some examples of people who post some really great twitter articles:

@Astro_Mike An Austronoaut tweeting from orbit
@tferriss Author and blogger on lifestyle design
@612brisbaneMy local ABC radio station

Oh, and if you're interested, I'm on twitter as @NeilEnnis

ObSrv: Server Problems Fixed

I apologise for the unavailability of ObSrv.com over the last few days.

Our server failed, so we bought a new server, which also failed.

Not being one to give up easily, I've been on this issue since Friday lunchtime, and am relieved to say that as of about 10pm last night, everything is now working fine.

On the bright side, we have a larger, faster server so things should run much better than before.

RSS Feed Do's and Don'ts

To the right you can see a screen shot of three RSS feeds as seen on my iGoogle page. Two of them are good, one of them is not so good. Can you tell the difference?

They're all really specific in nature. The first one just shows breaking news as reported by the ABC. The second shows recent posts made be people about cruises in Australia via the CruiseCritic.com message boards, and the third shows new posts to the "General Cruise Discussions" section of the OzCruiseCritics message boards.

With the ABC feed, whenever there's a new story, it appears at the top of the list, pushing older stories off the bottom of the list.

Same with the Cruise Critic feed (the 2nd one). As a new post is received on a particular subject, that subject goes to the top of the list, pushing older ones off the bottom.

The problem with the third feed ("General Cruise Discussions") is three-fold:

1. The name of the feed doesn't do OzCruiseCritics justice. Anyone casting a quick glance at the feed doesn't know where it's from. With the first two feeds on this example, it's quite plain who's supplying them, but not the third feed.

2. The discussion topics are not formatted properly. The name of the feed is repeated in each of the item descriptions. E.g. you see "General Cruise Discussions :: Re: Queensland Cruise" and "General Cruise Discussions :: Re Snorkelling". This is redundant. We already know what feed the item is coming from by looking at the title of the feed. Each of these items should have a more concise description. In this case they should be "Queensland Cruise" and "Snorkelling".

3. You can't see it from the picture, but take my word for it, whenver someone replies to a topic on the OzCruiseCritics feed, it generates a new feed item. So if I was to reply to the "Snorkelling" discussion, the feed would end up looking like this:

General Cruise Discussions :: RE: Snorkelling
General Cruise Discussions :: RE: Queensland Cruise
General Cruise Discussions :: RE: Snorkelling

I think that is crowded and difficult to read. What should really happen is that if an item is updated, it goes to the top of the list, and the old version of that item is removed from the list. So the feed should look like this:

Snorkelliung
Queensland Cruise

These suggestions might seem pedantic, but the whole aim of RSS is to get your content read. Whish means the info needs to pack as much punch as possible, with as little clutter as possible. The reward for this is that your message gets out, more people hear what you say, and you get more traffic to your site.

ObSrv: Improved image search

I just fixed a couple of minor bugs which were preventing ObSrv from serving up images based on advanced google image searches.

They should be working ok now.

If you still have any problems, please let me know or reply to this post.

ObSrv: Getting an RSS feed from ANY site with images

I mentioned earlier that I'd modify ObSrv to be able to generate an RSS feed from any site that has images.

I didn't realize it, but it already does this.

Just key in the search words, followed by site:yourdomain.com

For example, if you want a feed of all images of the planet Saturn from Nasa.gov, just type in:
Saturn site:nasa.gov

Or for a feed of all images of Antarctica from NationalGeographic.com, type in:
Antarctica site:nationalgeographic.com

How cool is that?

ObSrv: Some example image feeds

Here's some slideshows built on image feeds from ObSrv. If you've got some you'd like to show the world, please send an email to mail {at] ObSrv [d0t} com and I'll be happy to showcase it here for you.