ember need to refresh browser to get the model data

I follow the ember guide and with a little modification to show the post data. I defined a posts route which will generate links and a post route with dynamic segment to show the detail. however, if I click the link '/posts/1', it navigates to the post route with id. however, I do not see the post detail unless I refresh the browser. does anyone knows why? and can anyone explain what the route serialize hook does? I do not understand the explanation from the ember guide.

Handlebars

<script type="text/x-handlebars">
    <h2>Welcome to Ember.js</h2>

    {{outlet}}
  </script>

  <script type="text/x-handlebars" id="posts">
    <ul>
    {{#each post in model}}
      <li>{{#link-to 'post' post}}{{post.name}}{{/link-to}}</li>
    {{/each}}
    </ul>
  </script>

  <script type="text/x-handlebars" id="post">
    <ul>
    {{#each post in model}}
      <h1>{{ post.name }} - {{ post.age }}</h1>
    {{/each}}
    </ul>
  </script>

Ember Code

App = Ember.Application.create();

App.Router.map(function() {
  this.resource('posts');
  this.resource('post', { path: '/posts/:post_id' });
});

App.PostsRoute = Ember.Route.extend({
    model: function () {
        return [{
            id: 1,
            name: 'Andy',
            age: 18
        }, {
            id: 2,
            name: 'Tom',
            age: 14
        }, {
            id: 3,
            name: 'John',
            age: 10
        }];
    }
});

App.PostRoute = Ember.Route.extend({
    model: function (params) {
        var obj = [{
            id: 1,
            name: 'Andy',
            age: 18
        }, {
            id: 2,
            name: 'Tom',
            age: 14
        }, {
            id: 3,
            name: 'John',
            age: 10
        }];
        return obj.filter(function (item) {
            return item.id === parseInt(params.post_id);
        });
    },
    serialize: function(model) {
        // this will make the URL `/posts/12` WTH is this mean????
        return { post_id: model.id };
    }
});